Synthesis and Consolidation of Boron Carbide- A Review

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Synthesis and consolidation of boron carbide:a review

A. K. Suri, C. Subramanian*, J. K. Sonber and T. S. R. Ch. Murthy

Boron carbide is a strategic material, finding applications in nuclear industry, armour for

personnel and vehicle safety, rocket propellant, etc. Its high hardness makes it suitable for

grinding and cutting tools, ceramic bearing, wire drawing dies, etc. Boron carbide is

commercially produced either by carbothermic reduction of boric acid in electric furnaces or

by magnesiothermy in presence of carbon. Since many specialty applications of boron carbide

require dense bodies, its densification is of great importance. Hot pressing and hot isostatic

pressing are the main processes employed for densification. In the recent past, various

researchers have made attempts to improve the existing methods and also invent new processes

for synthesis and consolidation of boron carbide. All the techniques on synthesis and

consolidation of boron carbide are discussed in detail and critically reviewed.

Keywords: Synthesis, Densification, Boron carbide, Sintering, Hard material, Neutron absorber

IntroductionBoron carbide is a suitable material for many highperformance applications due to its attractive combina-tion of properties such as high hardness (29?1 GPa),1

low density (2?52 gm cm23),1 high melting point(2450uC),2 high elastic modulus (448 GPa),3 chemicalinertness,2,4 high neutron absorption cross-section (600barns),4,5 excellent thermoelectric1,4 properties, etc. Ithas found application in the form of powder, sinteredproduct as well as thin films. Boron carbide (also knownas black diamond) is the third hardest material afterdiamond and cubic boron nitride. Its outstandinghardness makes it a suitable abrasive powder forlapping, polishing and water jet cutting of metals andceramic materials.4

Tools with boron carbide coating are used for cuttingof various alloys such as brass, stainless steel, titaniumalloys, aluminium alloys, cast iron, etc.1 In sinteredform, it is used as blasting nozzles,6 ceramic bearingsand wire drawing dies due to good wear resistance.1 Thecombination of low specific weight, high hardness andimpact resistance makes it a suitable material as bodyand vehicle armour. Modulus to density ratio of boroncarbide is 1?86107 m, which is higher than that of themost of the high temperature materials and hence itcould be effectively used as a strengthening medium.7

Thin films of boron carbide find application asprotective coating in electronic industries.8,9

Boron carbide is extensively used as controlrod, shielding material and as neutron detector innuclear reactors due to its ability to absorb neutronwithout forming long lived radionuclide.7,10–17 Neutron

absorption capacity of boron carbide can be increasedby enriching B10 isotope. Composite material containingboron carbide with good thermal conductivity andthermal shock resistance are found suitable as first wallmaterial of nuclear fusion reactors.18–21 Boron carbidebased composites are potential inert matrix for actinideburning.22 Boron carbide is also used for treatment ofcancer by neutron capture therapy.23

As it is a p-type semiconductor, boron carbide isfound to be a potential candidate material for electronicdevices that can be operated at high temperatures.24,25

Owing to its high Seebeck coefficient (300 mV K21),boron carbide is an excellent thermoelectric material.26

Boron carbide is finding new applications as thermo-couple, diode and transistor devices as well. Boroncarbide is an important component for the productionof refractory and other metal borides.27–29 The lowdensity, high stiffness and low thermal expansioncharacteristics of B4C make it attractive Be/Be alloyreplacement candidate for aerospace applications.30

Thevenot has compiled a comprehensive review onboron carbide1 in 1990, in which synthesis, consolida-tion, analytical characterisation, phase diagrams, crystalstructure, properties and applications are discussed. Thispaper critically examines various methods of synthesisand consolidation of boron carbide and discusses theirmerits and demerits along with structure, properties andapplications.

Structure of boron carbideThe bond between B-B atoms and B-C atoms play a keyrole in deciding the crystal structure and properties ofboron carbide. Knowledge of these will help us inunderstanding the complexities involved in processingand achieving the desired properties. Boron carbide is acompositionally disordered material that exists as

Materials Group, Bhabha Atomic Research Centre, Mumbai 400085, India

*Corresponding author, email [email protected]

� 2010 Institute of Materials, Minerals and Mining and ASM InternationalPublished by Maney for the Institute and ASM International

4 International Materials Reviews 2010 VOL 55 NO 1 DOI 10.1179/095066009X12506721665211

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rhombohedral phase in a wide range of composition,which extends from B10?4C (8?8 at.-%C) to B4C(20 at.-%C).31–34 Among them, B4C is superior inproperties such as hardness, thermal conductivity etc.Since B4C is in equilibrium with free carbon and is onlyboundary between BnC and BnCzC (where 4,n,10),35

synthesis of B4C without free carbon is a great challenge.Carbon content of boron carbide greatly influences thestructure and the properties of the compound and hencethe exact knowledge of B/C ratio of the phase is veryimportant. But the analytical study of B-C system isdifficult due to extreme hardness and chemical stabilityof boron and boron carbide phases.33 Different limits ofhomogeneity range are reported by researchers at thecarbon rich side of boron carbide, corresponding toB4?3C (18?8%C),36 B4?0C (20%C),33,34 and B3?6C(21?6%C).37 Difficulties associated with the estimationof free and combined carbon could be accountable forthese inconsistent results.36 B-C phase diagram showinghomogeneity range from 8?8 to 20 at.-%C, as generatedby Bouchacourt et al.34 is presented in Fig. 1.

Crystal structureThe most widely accepted crystal structure of boroncarbide is rhombohedral, consisting of 12-atom icosahe-dra located at the corners of the unit cell. Schematicdiagram of the structure of boron carbide is presented inFig. 2.38 The longest diagonal of the rhombohedral unitcell contains three atom linear chain (C-B-C). Each endmember of the chain is bonded covalently to an atom ofthree different icosahedra.31 In general, icosahedraconsist of 11 boron atoms and one carbon atom. Thelocations of carbon atoms within different icosahedraare not ordered relative to one another. The icosohedralconfiguration is the result of a tendency to form three-centre covalent bonds due to deficiency of valenceelectrons of boron.39 Two crystallographically in-equivalent sites exist in the icosahedron. Six atomsreside in two polar triangles at the opposite ends of theicosahedron and the remaining six atoms occupyequatorial sites. The atoms at polar sites are directlylinked to neighbouring icosahedra via strong two-centrebonds along the cell edges. The atoms in equatorial siteseither bond directly to other icosahedra through three-centre bonds or to chain structures.40,41 Most of theicosahedra have a B11C structure with the C atom placedin a polar site, and a few percent have a B12 structure ora B10C2 structure with the two C atoms placed in twoantipodal polar sites.41

Three types of three-atom chain are envisioned: C-B-C, C-B-B and B-B-B. Variation in carbon concentrationchanges the distribution of three-atom chains.31 B4C(20%C) structure consists of B11C icosahedra and C-B-Cchains. As the composition becomes rich in boron,carbon of the B11C icosahedra is retained, while one ofthe carbon atoms on the C-B-C chains is replaced byboron. Near the composition B13C2, the structureconsists of B11C icosahedra and C-B-B chains. Onfurther carbon reduction, some of the B11C icosahedraare replaced by B12 icosahedra retaining the C-B-Bchain.40,42 Carbon-boron bonds present in the threeatom chains are much stronger than boron-boron bondin icosahedra.40 The inter-icosahedra bonds are stifferthan the intra-icosahedra bonds.43

Conflicting views still exist concerning the nature ofsite occupancies. A model based on early X-ray dif-fraction data44,45 proposed that the B4C composition ismade up of B12 icosahedra and C-C-C chains. Howeverlater studies38,40–42,46,47 based on improved X-ray andneutron diffraction, nuclear magnetic resonance studies,theoretical calculations and vibrational spectra indicatethat the structure consist of B11C icosahedra and C-B-Cchains. Even among those who favour B11C icosahedraand CBC chain model for 20 at.-% (B4C), there isdisagreement on the structural changes that occur inboron carbides, as the carbon content is decreasedtowards 13 at.-% (B13C2). Some workers46,48 proposethat carbon atoms are removed from the icosahedra toform B12 icosahedra, while others40,42,49 propose thatcarbon atom is replaced from three atom chains. Owingto similarity of boron and carbon in electron density andnuclear cross-section (B11 and C12), both X-ray andneutron diffraction studies are not very successful in

1 Phase homogeneity range in B-C phase diagram: rep-

rinted with permission from Elsevier, J. Less Comm.

Met., 1979, 67, Fig. 2 in p. 329

2 Schematic diagram of structure of boron carbide

Rhombohedral unit cell, consisting of 12-atom icosahe-

dra located at the corners and C-B-C linear chain at

the diagonal of the unit cell is shown. Within the icosa-

hedron, six atoms reside in two polar triangles at the

opposite ends of the icosahedron and the remaining

six atoms occupy equatorial sites: reprinted with per-

mission from the American Physical Society, Phy. Rev.

Lett., 1999, 83, (16), Fig. 1 in p. 3230

Suri et al. Synthesis and consolidation of boron carbide: a review

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unambiguously assigning the exact site occupancies.48

The concentration of B12 and B11C icosahedra and C-B-C and C-B-B chains vary and chainless unit cells alsooccur.50,51 Variation of structure elements B12, B11C, C-B-C and C-B-B in boron carbide unit cell with C contentis shown in Fig. 3.51 The carbon rich limit of homo-geneity range which was assumed to contain B11Cicosahedra and C-B-C chains only, also contains 19% C-B-B chains. The composition of B6?5C which wasattributed to be the most representative structure (B12,C-B-C) and used for many model calculations has beenproved to be the least defined structure containing60%B11C and 40%B12 icosahedra. These structuralchanges could also explain the abrupt decrease inthermal conductivity between B4C to B6?5C. Saalet al.46 have recently applied ab initio calculations toevolve the structure of boron carbide for the entirecomposition range. The enthalpy of formation andlattice parameters were calculated and compared withthe experimental data. For carbon rich composition(20%C), B11C-CBC structure and for 13?33%C compo-sition B12-CBC structure were found most stable. Itsuggests that carbon atom is gradually replaced byboron in icosahedra. This result is contradictory withother researchers who suggest that carbon atom isreplaced from chain. At boron rich end, enthalpy andlattice parameters of B12 BVaC (Va denotes vacancy)structure is in good agreement with the experimentalvalues for boron carbide having 7?14 at.-%C. Since theenthalpy of formation of B12 BVaC is positive it ispredicted that B12 BVaC’s composition cannot bereached by boron carbide and instead, pure boron willprecipitate out, which is in agreement with experimentalphase equilibrium. Radev et al.43 have found that metalcations can replace a part of boron atoms in icosahedraposition and thus improves the stiffness, hardness andwear resistance of boron carbide.

Recent observations by Raman spectroscopy suggeststructural phase transformation and the formation oflocalised amorphous phase which is weaker than theoriginal crystalline phase under conditions of loading.52

First principle molecular dynamics simulations haverevealed that the depressurisation amorphisation resultsfrom pressure induced irreversible bending of C-B-Cchains.53

Structure sensitive propertiesThermal and electrical conductivity, heat capacity,hardness, etc. strongly depend on structure of boroncarbide and the variations are brought out in thefollowing lines. Lattice parameter aR of rhombohedralunit cell decreases with increase in carbon content butthe plot is discontinuous at the composition B13C2

(13?33 at.-%C). Density of boron carbide increaseslinearly with carbon content within the homogeneityrange of the phase according to the relation d(g cm23)52?422z0?0048[C] at.-% (r50?998) with8?8 at.-%([C]>20?0 at.-%. The number of atoms perunit cell is exactly 15 for B4C, but increases with theboron content and approaches 15?3 for the boron richlimit B10C.35 Hardness of boron carbide increases withcarbon within the homogeneity range as the structurebecomes stiffer.1 Shear modulus of boron carbideincreases with carbon from 185 GPa for B6?5C (13%C)to 198 GPa for B4?3C (20%C).54 Fracture toughness andYoung’s modulus also increases with the carboncontent.1

Heat capacity of boron carbide increases withdecrease in carbon within the homogeneity range. Thisincrease is due to the change in lattice vibration modeproduced by reduction of the stiffness of the three-atomchain accompanied with a change from C-B-C to C-B-B.55 Thermal conductivity of B4C (20%C) falls withtemperature in the manner characteristic of crystallineceramics. However, thermal conductivity of boroncarbide with low carbon is relatively less and tempera-ture independent, a behaviour more characteristic ofamorphous materials. These differences of thermaltransport can be explained if it is assumed that, thethermal conductivity is dominated by the transfer ofvibrational energy through the inter-icosahedral chainsrather than within the softer icosahedra. As the C-B-Cchains are inhomogeneously replaced by C-B-B chains atransition takes place from crystal-like transport toglass-like transport. Moreover thermal conductivity fallsbecause B-B bonds are much softer than C-Bbonds.40,55,56 Gilchrist et al.57 have found that thermalconductivity of B4C falls from 29 W m21 K21 at roomtemperature to 12 W m21 K21 at 1000uC. Thermalconductivity increases when 10B isotope replaces 11B inboron carbide. This is attributed to the increase in thebonding energy per unit mass and the phonon velocityas a lighter isotope is substituted for a heavier isotope.58

Electrical conductivity in boron carbide was studiedby Wood et al.49 and Matusi et al.55 Charge carriers inboron carbide are holes which form small polarons andmove by phonon assisted hoping between carbon atomslocated at geometrically non-equivalent sites.49 The non-equivalence arises from two sources. First, carbon atomscan be distributed among non-equivalent sites withinB11C icosahedra. Second, only a fraction of the availablepositions of inter-icosahedral chain is generally filled byC-B-C chains. The carbon rich limit (B4C) resembles anideal crystal and therefore has the lowest electricalconductivity.55 Electrical conductivity increases withtemperature, which is the sign of behaviour of asemiconductor. Density of small polaron holes is

3 Composition of structure elements (B12 and B11C ico-

sahedra, C-B-C and C-B-B chains) in boron carbide unit

cell and chainless unit cells with variation of C con-

tent: reprinted with permission from Elsevier, Solid

State Commun., 1992, 83, Fig. 4 in p. 850


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independent of temperature but the mobility of holesincreases with temperature. Within the homogeneityrange, charge carrier density and electrical conductivitydecreases with increase in carbon content. The tempera-ture dependence of electrical conductivity is essentiallyindependent of carbon concentration.49

Irradiation responseNeutron irradiation of boron carbide results in extensiveintergranular cracking due to the formation of heliumbubble as per the following equation59–61

5B10z0n1?3Li7z2He4z2:6 MeV (1)

Formation of these cracks, which prevent heat conduc-tion and the atomic disorder resulting in high phonondispersion, decrease the thermal conductivity duringirradiation.59 The anisotropic precipitation of heliumnot only changes the microstructure but degrades themechanical and physical properties as well. When grainboundary cracking occurs, a large amount of trappedhelium is released simultaneously with the occurrence ofbulk swelling.62,63 Considerable amount of tritium isproduced in B4C by fast neutron irradiation, which isretained up to 700uC even on annealing and is releasedonly at temperature higher than 900uC.62,64 Copelandet al.65,66 have reported that irradiation of boron carbidewith neutron causes lattice strains due to the formationof lithium and helium as reaction product as well assome atomic displacements. Inui et al.67 have reportedthat a complete crystalline to amorphous transitiontakes place by electron irradiation with energy .2 MeVand at temperature ,163 K. They also found that theamorphous boron carbide remains in amorphous stateon annealing at 1273 K. They suggested a possibility,that, in boron carbide, the individual B12 icosahedrathemselves are not destroyed by electron irradiation buttheir regular spatial arrangement in the B12C3 lattice isperturbed and is gradually put in disorder withincreasing electron dosage, resulting in an amorphousstate.67 Froment et al.59 have noticed that boron richB8C is more resistant to radiation damage compared toB4C and hence becomes a possible candidate for newabsorbing materials. 11B4C is found to be very stableafter fast neutron irradiation in reactors. Dimensionalchanges and thermal conductivity of 11B4C are substan-tially smaller than that of 10B4C.68

Synthesis of boron carbideBoron carbide was discovered in nineteenth century as abyproduct of reaction involving metal borides. Thepurity of boron carbide produced by early researcherswas less than 75% and in 1933, Ridgway69 claimed tohave produced crystalline B4C of 90% purity bycarbothermic process. Lipp4 has presented a review ofboron carbide production, properties and applicationsin 1965. Spohn70 has also mentioned the synthesis routesfor boron carbide production and its uses in his article.In this section, different routes for B4C synthesis will bediscussed. The methods of boron carbide synthesis areclassified as:

(i) carbothermic reduction(ii) magnesiothermic reduction

(iii) synthesis from elements(iv) vapour phase reactions(v) synthesis from polymer precursors

(vi) liquid phase reactions(vii) ion beam synthesis

(viii) VLS growth.

Carbothermic reduction of boric acidCarbon reduction of boric acid and boron trioxide is thecommercial method for the production of boroncarbide. The overall carbothermic reduction reactioncan be presented as follows

4H3BO3z7C?B4Cz6COz6H2O (2)

This reaction proceeds in the following three steps70

4H3BO3?2B2O3z6H2O (3)

B2O3z3CO?2Bz3CO2 (4)

4BzC?B4C (5)

Boric acid on heating converts to B2O3 by releasingwater. The reduction of B2O3 with carbon monoxidebecomes thermodynamically feasible above 1400uC. Thefurnace temperature is usually maintained at .2000uCto enhance the rate of overall reaction. The process ishighly endothermic, needing 16 800 kJ mol21 B4C.71

Three types of electric heating furnaces, namelytubular, electric arc and Acheson type (graphite rod asresistance element) are used for the production of boroncarbide. Tubular electric furnaces using graphite tubesas heating element are in use for carrying out reactionsfor scientific study only. These furnaces are limited insize, dependent on the size of the availability of graphitetubes. Hence large scale production is not feasible usingtubular furnaces.

Arc furnace process

Electric arc furnace process for making boron carbidehas been patented by Schroll et al.72 in the year 1939,wherein the mixture of boric acid and petroleum coke ismelted in an arc furnace followed by crushing theresultant product and mixing it with substantially thesame quantity of boric acid and remelting the mixture asecond time. The design and operation of the electric arcfurnace for the large scale production of boron carbidehas been explained by Scott.73 In the arc furnaceprocess, the temperatures are generally very high dueto localised electric arcs, which are responsible for heavyloss of boron by evaporation of its oxides. Moreover theproduct obtained is chunks of melted boron carbide,which needs subsequent laborious crushing and grindingoperations.

Acheson type furnace

Acheson type furnaces, where a graphite rod is used asheating element, surrounding which the reactants arecharged is also used for production of boron carbide.Early patents by Ridgway69,74 give the details of thefurnace and the process. Operational details of theAcheson furnace are explained below. Partially reactedcharge from the previous run is assembled around thenew graphite heating rod. Above this, the new chargemixture consisting of boric acid and carbon is added. Onheating, the reaction initiates near the graphite rod andcarbon dioxide escapes to the atmosphere through thecharge above. As the reaction proceeds, the charge getsheated by conduction as well as by the heat of the



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escaping CO. Boric acid initially loses its water andconverts to B2O3. On further heating, B2O3 melts andforms a glassy film preventing the escape of CO from thereduction zone. The product gases form bubbles andgrow in size near or just above the reaction site and asthe pressure increases, the bubbles burst pushing thecharge above. During these bursts some of the partiallyreacted charge is thrown out of the furnace and boronalso escapes to the atmosphere in the form of boronoxide vapours. These bubble bursts and evaporationlosses affect the efficiency of the process considerably.

After completion of the run, the top is broken openand the boron carbide surrounding the graphite rod ismanually collected. Operator experience plays a majorrole in identifying the completely reacted product so thatless amount of oxides enter the boron carbide portion.The reacted product is crushed in jaw crushers andfurther ground to finer size. Ground powder is washedin water and leached in acid to remove the contamina-tion due to grinding media and also the accompanyingunreduced or partially reduced oxides of boron from thereduced product. In each run, only a small portion of thecharge gets converted to carbide and the balancematerial is recirculated in further runs. Some quantityof boron oxides escapes to the atmosphere along withcarbon monoxide. Hence in this process, conversion ineach run is low and boron loss is high. As the rawmaterials used are cheap and the process is simple, thisprocess has been adopted for commercial production.Though the method of raw material charging andcollection of reacted product could be different in arcfurnace and Acheson processes, the reaction sequence isvery similar.

As temperature is an important process parameter incarbothermic reduction process and the heat transferplays an important role in the formation of boroncarbide Rao et al.75,76 have devised a method of coretemperature measurement in boron carbide manufactur-ing process. They have analysed the heat transferprocess inside the reactor and the effect of it on theformation of boron carbide based on the recorded data.

Process kinetics

Kinetics of the reaction and also the product quality isstrongly influenced by porosity of the charge, type ofcarbon used for reduction, rate of heating and the finalcore temperature. Process kinetics, influence of processparameters and the means of improving the productquality and conversion efficiency have been investigatedby many researchers. Petroleum coke is found to be abetter reducing agent than graphite, charcoal andactivated charcoal.77 Boric acid to coke ratio of 3?3–3?5 is found optimum and at higher ratios, though boroncarbide free of carbon could be obtained, recovery ispoor. Alizadeh et al.78 have optimised the boron oxide/carbon (petroleum coke) ratio to yield boron carbidewith low (0?65%) carbon. Addition of small amount ofsodium chloride (1?5%) is found to be effective inincreasing the yield.71,79 Start of formation of B4C hasbeen noticed by Subramanian et al.80 at 1200uC bythermogravimetric studies on the reduction of boric acidby petroleum coke in vacuum. Figure 480 shows theweight change of the charge with temperature up to1400uC. Formation of boron carbide by carbothermicreduction is highly dependent on the phase changes ofreactant boron oxide from solid to liquid to gaseousboron sub oxides and the effect of reaction environment(heating rate and ultimate temperature).81 Slow heating(,100 K s21) of the charge results in the formation ofboron carbide by a nucleation and growth mechanism asthe reaction proceeds through a liquid boron oxide path.Intermediate heating rates (103 to 105 K s21) result inthe formation of both large and small crystallites,indicating the reaction of carbon with both liquid boronoxide and gaseous boron suboxides. Rapid heating rates(.105 K s21) result in smaller crystallite size, indicatingthe occurrence of reaction through gaseous boronsuboxides.

Dacic et al.82 have studied the thermodynamics of gasphase carbothermic reduction of boron anhydride. B2O2

and BO are formed by carbothermic reduction of B2O3

according to reactions (6) and (7) and then reduced to Bor B4C.

4 Thermogravimetric analysis plot of carbothermic reduction of boric acid80



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B2O3zC?B2O2zCO (6)

B2O3zC?2BOzCO (7)

The effect of the feed composition and temperature onthe product composition in carbothermic reduction isshown in Fig. 5.82 A decrease in the partial pressure ofCO facilitates synthesis of B4C by boosting thegeneration of B2O2 and BO.

Production of boron carbide by carbothermy has beenessentially a batch process. Tumanov83 has reported thedevelopment of a continuous process for the productionof boron carbide, by direct inductive heating of a chargemade of boron oxide and carbon black. An alternatereduction method patented by Rafaniello84 explains theprocess for producing submicrometre size boron carbidepowders. The type of carbon used, method of prepara-tion of the charge mixture and the fast heating rates (70–10 000uC min21) are responsible in obtaining finepowders. Weimer et al.85,86 have designed a verticalapparatus comprising of cooled reactant transportmember, reaction chamber, heating element and coolingchamber for the continuous production of submicro-metre B4C powder. Modelling of carbothermic reduc-tion process for the production of boron carbide has notbeen attempted by anybody so far.

Preparation of dense articles need fine boron carbidepowders in micrometre size. The product of conven-tional process has to undergo series of size reductionprocesses to obtain such powders. Such grinding opera-tions contaminate the product necessitating additionalpurification steps. Availability of nanosized powders willnot only avoid the grinding operations but also reducethe temperature of densification substantially.

Nanocrystalline boron carbide

Preparation of nanosized particles of boron carbide is ofrecent interest. B4C particles in the nanosize range(260 nm) can be prepared by reduction of B2O3 vapourby carbon black at 1350uC.87 Above this temperature,yield is low due to loss of B2O3 from reaction mixture.Addition of cobalt as catalyst is found to be helpful in

yield of nanorods.88 Ma et al.89 have prepared highpurity boron carbide nanowires from mixed powderprecursor containing boron, boron oxide and carbonblack. The mixture is heated quickly to 1650uC and heldat that temperature for 2 h under flowing argon.Vapours of B2O3, B2O2 and CO react to form B4C solidnanowires with a mean diameter of y50 nm and lengthsof several hundreds of micrometres (Fig. 6).89 Largescale boron carbide nanowires of size 80–100 nmdiameter and 5–10 mm in length have been synthesisedusing B/B2O3/C powder precursor under argon flow at1100uC.90 Xu et al.91 have synthesised nanostructures ofboron carbide by heating B2O3 powder to 1950uC in agraphite crucible covered with a boron nitride disc.Majority of the crystallites deposited on boron nitridedisc show a belt-like morphology with average widthand length of about 5–10 and 50–100 mm, while thethickness was in the nanoscale range (20–100 nm). Anumber of perfect icosahedral quasicrystal particles(Fig. 7a)91 and multiply twinned particles normally inrod shape were also present (Fig. 7b).91 These particleshave very large sizes (y20 mm). Thus it was found thatwhen the reaction takes place in gas phase or theproduct could be nanocrystalline B4C. Presence of somecatalyst also promotes the formation of nanopowders.

Although carbothermic reduction results in loweryield due to loss of boron in the form of its oxides, thisroute is adopted as commercial method mainly becauseof the simple equipments and cheap raw materials whichmake this route the most economical. This route is notonly useful for commercial powder production but alsofor the production of nanocrystalline B4C. Details ofexperimental studies on carbothermic reduction, givingcharge composition, processing conditions and productquality of boron carbide obtained by various researchersare summarised in Table 1.69,72,77–79,83–85,92

Magnesiothermic reduction of B2O3

An alternate method for the production of boroncarbide is by magnesiothermic reduction of boronanhydride in presence of carbon as given below

2B2O3z6MgzC?B4Cz6MgO (8)

This reaction takes place in two steps:step 1

2B2O3z6Mg?4Bz6MgO (9)

step 2

4BzC?B4C (10)

The reaction is exothermic (DH51812 kJ mol21) innature. As the vapour pressure of magnesium is highat the reaction temperature of .1000uC, a cover gassuch as argon or hydrogen is used and also the systempressure maintained high. The products of the reactionare processed by aqueous methods to remove magne-sium oxide from boron carbide. The carbide is stillcontaminated with magnesium borides formed as stablecompounds. This reduction technique yields very fineamorphous powder, which is well suited for use in thefabrication of sintered products. One method ofcontrolling the temperature and the particle size of theproduct is by choosing the right size of the reactants.Post reductive sintering at temperatures 200–300uC

5 Effect of feed composition and temperature on calcu-

lated product composition in carbothermic reduction of

1 mol B2O3 (l) as per Dacic et al.:82 reprinted with per-

mission from Elsevier, J. Alloys Compd, 2006, 413,

Fig. 2 in p. 200



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higher than the reaction temperature increases theparticle size of the product. Seeding of the charge witha small quantity (1–2%) of boron carbide has been foundto increase the growth of B4C particles and the yieldsignificantly.93

An early patent by Gray94 explains the process for theproduction of boron carbide powders by magnesiothermicreduction of B2O3 or alkali Na2B4O7 in presence of carbon

at 1650–1700uC. Addition of metallic sulphates as catalysthas been found to reduce the reaction temperature to700uC.95 The heat of magnesiothermic reaction is sufficientenough for self high temperature synthesis route.Formation of ultra fine B4C powder from the stoichio-metric mixture of H3BO3, Mg and C by self-propagatinghigh temperature synthesis (SHS) has been studied byZhang et al.96 and Khanra et al.95,97 The ignitiontemperature of this mixture was found to be 670uC bythermal analysis method. Mechanical alloying has alsobeen utilised as a means of synthesising submicrometreB4C particles by magnesiothermic reduction.98

Wang et al.99 have studied the synthesis of B4C fibre–MgO composites by combustion of B2O3zMgzCfibre

samples in an argon filled chamber. The degree ofconversion was influenced by pressure of the ambientargon gas which influences the evaporation of magne-sium and thereby the combustion temperature andconversion. Calcium can also be used as reductant inplace of Mg. Berchman et al.100 have recently reportedsynthesis of boron carbide powder by calciothermicreduction of borax (Na2B4O7) or B2O3 in presence ofcarbon at 1000uC in argon.

Though boron carbide has been produced by magne-siothermic reduction and used for applications definedby its high calorific value, the high cost of magnesiumwill soon make this process obsolete for regularproduction. Table 293–99 presents a summary of studieson synthesis of boron carbide by magnesiothermicreduction.

Synthesis from elementsSynthesis of boron carbide from its elements isconsidered uneconomical due to the high cost of

a,b long straight segments; c,d curly tufts6 Image (SEM) of high purity single crystalline boron carbide nanowires formed by thermal evaporation of B/B2O3/C pow-

der precursor at 1650uC under argon atmosphere:89 reprinted with permission from Elsevier, Chem. Phy. Lett., 2002,

364, Fig. 1 in p. 315

7 a perfect icosahedral B4C particle and b rod shaped

twinned particles by carbothermic reduction of B2O3

(scale bars: 10 mm):91 reprinted with permission from

American Chemical Society, J. Phys. Chem. B, 2004,

108B, Fig. 4 in p. 7653



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elemental boron and hence employed for specialisedapplications101,102 only, such as B10 enriched or verypure boron carbide. For synthesis of enriched boroncarbide, carbothermic reduction is not suitable due toloss of boron as well as boron hold-up in the furnaceand hence this process is the only suitable economicalmethod. Although formation of boron carbide from itselements is thermodynamically possible at room tem-perature, the heat of reaction (239 kJ mol21) is notsufficient to carry out in a self-sustaining fashion.103

Formation of boron carbide layer slows down furtherreaction, due to slow diffusion of reacting speciesthrough this layer, thus necessitating high temperatureand longer duration for complete conversion of theelements into the compound. For synthesis fromelements, boron and carbon are thoroughly mixed toform uniform powder mixture, which is then pelletisedand reacted at high temperatures of .1500uC in vacuumor inert atmosphere. The partially sintered pellet ofboron carbide is then crushed and ground to get fineB4C powder. To achieve a high purity product of B4C,high purity elemental boron powder produced by fusedsalt electrolytic process104,105 is often used.

Mechanical alloying of B–C mixtures followed byheat treatment is one of the methods being investigatedfor the synthesis of boron carbide. Room temperaturemilling is carried out in planetary mills for prolongedduration to activate the powders and the alloyed mixtureis then annealed to obtain boron carbide. Spark plasmasynthesis is a new technique, in which a pulsed high dccurrent is passed through the charge mixture containedin a cavity along with the application of uniaxialpressure. In this process, the start and completion offormation has been noted at 1000 and 1200uC respec-tively. Combination of mechanical alloying followed byspark plasma sintering has been studied by Hian et al.106

to obtain 95% pure boron carbide.

Shock wave technique has also been attempted forboron carbide synthesis from amorphous boron andgraphite powder107 using trimethyl enetrinitramine asdetonator. The resultant product exhibited severaldifferent morphologies, such as filaments, distortedellipsoid, plates and polyhedron particles of nanosize.In this technique reactants are kept inside a steelcontainer which is placed in plastic tube. A detonatoris placed between container and the plastic tube.

Table 1 Charge composition, processing conditions and product quality on synthesis of boron carbide by carbothermicreduction*

Serialno. Reactants Process type Process parameters Product quality Ref. (year)

1 B2O3zPC Batch (resistancefurnace)

2400uC Crystalline B4C 90% pure 69 (1933)

2 H3BO3zcharcoal Batch (arc furnace) Melting temperatureof charge

Boron carbide with 15%C 72 (1939)

3 H3BO3zPC Batch 1470uC; HR:100uC min21, 5 h, Ar

Crystalline B4C 25–30 mm 79 (2004)

4 B2O3zPC/carbon active Batch 1470uC; HR: 100u min21,1–5 h, Ar

Crystalline B4C 25–30 mm 78 (2006)

5 B2O3 and carbon Batch 1800uC, 20–300 min, Ar Crystalline B4C without freecarbon

92 (2004)

6 H3BO3zPC Batch (Acheson) .2000uC Partially sintered and denseproduct B4C conversion:69–73%

77 (1986)

7 B2O3zcarbon black/graphite/activated charcoal

Continuous (inductionheating)

2227uC Crystalline B4C 83 (1979)

8 H3BO3zVulcan XC-72carbon black

Continuous 1820uC; HR: 900uC s21,3 min, Ar

Equiaxed crystals of 0.5 mm 84 (1989)

H3BO3zacetylene carbonblack

2000uC; HR: 1000–2000uC s21, 3 min, Ar

Submicrometre particles0.1–0.2 mm

H3BO3zactivated carbon 1580uC; HR: 755uC s21,3 min, Ar

Submicrometre and uniformsized crystals

9 H3BO3zcorn starch Continuous 1950uC, Ar Submicrometre particles0.1 mm

85 (1992)

Boric oxide and carbon 1850uC, Ar 0.02–0.1 mm

*PC: petroleum coke, HR: heating rate.

Table 2 Charge composition, processing conditions and product quality on synthesis of boron carbide bymagnesiothermic reduction*

Serialno. Reactants Process type Process parameters Quality of B4C Ref. (year)

1 B2O3zMgzC Tubular furnace 950–1200uC, H2 Fine powder 93 (2002)2 B2O3zMgzC SHS … Fine powder 98% pure 96 (2003)3 B2O3zMgzC Batch 700uC, Ar, 1 h catalyst: K2SO4 Boron: 74.6% Carbon: 25.2% 95 (1967)4 B2O3zMgzC Mechanical alloying Rotation speed: 200 rev min21 Submicrometre particles 88 (2006)

Ball to load ratio: 5 : 1 72 h5 B2O3zMgzCFibre Combustion synthesis Ar B4C fibrezMgO composites 99 (1994)6 H3BO3zMgzC SHS 670uC, Ar 8–24 mm size, 8% free carbon 97 (2005)7 Na2B4O7zMgzC Continuous 1650–1700uC, H2 Powder boron: 77.5% Carbon:

21.3%94 (1958)

*SHS: self-propagating high temperature synthesis.



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Initiation of explosive detonation was carried out by anelectric detonator. After the shock treatments, sampleswere recovered by shaving off the container with a lathe.In this technique very high heating and cooling rates areachieved along with high pressure. The chemicalreaction is completed in micro to milliseconds. Hencethis is suitable for the preparation of crystals of variousmorphology and non-equilibrium phases which are hardto be produced in thermal equilibrium conditions.

A few attempts have been noticed on the preparationof nanostructure boron carbide from its elements. Weiet al.108 have prepared boron carbide nanorods byreacting carbon nanotubes (CNT) with boron powder at1150uC under argon atmosphere. Chen et al.109 havesynthesised boron carbide nanoparticles by reactingmultiwall CNT with magnesium diboride at 1150uC for3 h in vacuum. At this temperature, magnesium diboridedecomposes and gives elemental boron. Recently Changet al.110 has attempted the preparation of boron carbidenanoparticles (200 nm) by direct reaction betweenamorphous boron and amorphous carbon at 1550uC.The crystals obtained had a high density twin structureswith variation of B/C ratio from particle to particle.

Table 3106–108,110–113 gives a comparative summary ofstudies reported on the synthesis of B4C from itselements. Synthesis of boron carbide from its elementsis suitable for the production of pure B4C. Though thecost of production is high due to the high cost ofelemental boron, for specialised applications such as innuclear industry this method is preferred.

Vapour phase reactionSynthesis of boron carbide by carrying out reactionbetween boron and carbon containing gaseous specieshas been extensively studied. This method is gainfullyadopted for the formation of boron carbide coatings andsynthesis of powders and whiskers in submicrometresizes. Boron halides such as BCl3, BBr3 and BI3 aresuitable boron source but BCl3 is the most preferred dueto its ready availability and low cost. Apart fromhalides, borane (B6H6) and oxide (B2O3) are also usefulboron sources. Hydrocarbon gases such as CH4, C2H4,C2H6, C2H2 and carbon tetra chloride (CCl4) areemployed as carbon source. Synthesis of boron carbidetakes place in the reaction chamber, which is kept at a

desired temperature, pressure and atmosphere.Generally hydrogen is present in the atmosphere, whichreacts with the halogen forming hydrogen chloride asper the following reactions

4BCl3zCCl4z8H2?B4Cz16HCl (11)

4BCl3zCz6H2?B4Cz12HCl (12)

4BCl3zCH4z4H2?B4Cz12HCl (13)

The flow of reactants and other process parametersdecide the composition and structure of the productformed.

One such set-up for vapour phase reaction isdescribed by Bourdeau in his patent.114 The process ofproducing boron carbide by reacting a halide of boronin vapour phase with hydrocarbon in the temperaturerange 1500–2500uC has been explained. Clifton et al.115

described a process for producing boron carbidewhiskers in the size range of 0?05 to 0?25 mm by thereaction of B2O3 vapours with the hydrocarbon gasbetween 700 and 1600uC. James et al.116 have patented aprocess for the production of boron carbide whiskersand the use of catalytic elements to enhance the yieldof the gas phase reaction process. Dieter et al.117 havedescribed a process for the production of boron carbidepowder of fine size with a surface area >100 m2 g21.MacKinnon et al.118 have reported that when borontrichloride is reacted with CH4–H2 mixture in a radiofrequency argon plasma, boron carbides of variable B/Cratios are obtained as submicrometre powders, theproduct stoichiometry depending on the reactantcomposition.

Chemical vapour deposition (CVD)

Deposition of different types of boron carbide films(B13C2, B4C, metastable phases, highly strained struc-tures, etc.) by CVD techniques has been reported inliterature. The actual deposition is controlled by masstransfer and surface kinetics, which affects the stoichio-metry and properties of the boron carbide phases grown.Graphite, single crystal silicon, carbon fibre and boronare the substrate materials used for thin film synthesis.Generally the process is carried out in vacuum in the

Table 3 Charge composition, processing conditions and product quality on synthesis of boron carbide from elements*

Serialno. Reactants Process type Process parameters Product quality Ref. (year)

1 Amor. boronzAmor.carbon

Solid state thermalreaction

1550uC, 4 h, Ar Nanoparticles15–350 nm

110 (2007)

2 BzC Hot pressing 1800–2200uC, 3–4 h Articles of neartheoretical density

111 (1975)

3 BzC MAzannealing MA for 90 h Annealingat 1200uC

B4C with someunknown peaks

112 (2006)

4 BzC MAzspark plasmasintering

1650uC, 16 min 95% dense pelletof high purity boroncarbide

106 (2004)

5 Amor. boronzcarbonblack

Spark plasma synthesis .1200uC, 10 min Sintered B4C,disordered finecrystalline

113 (2005)

6 Amor. boronzgraphite Shock wave technique Detonator: trimethylenetrinitramine Detonationvelocity: 6.4 km s21

Nanosized particlesof crystalline B4C

107 (1996)

7 Amor. boronzCNT Solid state reaction 1150uC, Ar Straight nanorods 108 (2002)

*Amor.: amorphous; MA: mechanical alloying; CNT: carbon nanotube.



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temperature range of 450 to 1450uC. Substrate tempera-ture has strong influence on the process and productquality. High substrate temperature results in pooradhesion whereas deposition rate is low at lowtemperature. Amorphous boron carbide coating can beobtained at a low temperature of y500uC whereascrystalline film is obtained at higher temperatures.1100uC. Amorphous boron carbide coatings on SiChave been obtained by CVD from CH4–BCl3–H2–Armixtures at low temperature (900–1050uC) and reducedpressure (10 kPa).119

Preparation of boron carbide fibres by the reaction ofboron halides with woven cloth of carbonisable materialin hydrogen atmosphere has been patented by Waineret al.120,121 Jaziehpour et al.122 have prepared boroncarbide nanorods on graphite substrate at 1400uC byCVD using charge mixture of boron oxide, activatedcarbon and sodium chloride. Shu-Fang et al.123 havegrown novel boron carbide nanoropes by CVD using o-carborane (C2H12B10) as precursor and ferrocene(C10H10Fe) as catalyst. Karaman et al.124 have studiedthe kinetics of CVD of B4C on tungsten substrate usingBCl3–CH4–H2 gas mixture. They proposed that twomajor reactions take place during the process

BCl3 gð Þz 1

4CH4 gð ÞzH2 gð Þ?

1

4B4C sð Þz3HCl gð Þ (14)

BCl3 gð ÞzH2 gð Þ?BHCl2 gð ÞzHCl gð Þ (15)

Reaction rate of boron carbide formation is lower thanthat of dichloroborane formation over the entire rangeof temperatures (1000 to 1400uC) studied. Schouleret al.125 obtained BCx (x>3) phase having whisker-likemorphology by reacting BCl3 and B6H6 at 1000uC onquartz substrate in presence of hydrogen and nickel.Sezer and Brand126 have written a comprehensive reviewon CVD of boron carbide. The mechanical, thermal andelectrical properties of CVD boron carbides are compar-able to other important refractory materials and promisea wide range of application areas, particularly in thenuclear industry. They have also discussed the thermo-dynamic modelling used by many researchers and haveconcluded that the process takes place far fromequilibrium and that, thermodynamic modelling is notsufficient to represent experimental deposition condi-tions. Table 4114–118,127–147 presents a summary ofstudies reported on vapour phase reaction synthesis ofboron carbide.

Many modifications such as laser CVD (LCVD),plasma enhanced CVD (PECVD), hot filament CVD(HFCVD), etc. have been tested for the formation ofboron carbide films.

Laser CVD

In this technique the energy of a laser beam is used toheat the surface of a substrate to the temperaturerequired for chemical deposition. It allows superbspatial resolution (y5 mm) because the chemical reac-tions are restricted to the heated zone created by thefocused laser spot, in contrast to the traditional CVDfurnace which heats the entire surface of the sub-strate.148 Laser CVD results in deposits with high purity,high degree of crystallinity, low porosity, excellent

mechanical properties and thermal stability. Theseattributes are the result of deposition occurring oneatom at a time. Deposition rates in LCVD techniquesare orders of magnitude higher than that in traditionalCVD. The deposition rate and surface microstructurestrongly depend on laser power and hydrogen content inthe gas phase.127 Control of laser power density allowsfor codeposition of r-(B4C) and disordered graphite,which can be beneficial for tailoring the thermal andelectronic properties of boron carbide.128 The reactiveatmosphere composition is the most important para-meter in laser CVD. When the relative amount ofcarbon to boron in the gas phase is high, a disorderedgraphitic phase is deposited along with boron carbideand when the carbon is low, tetragonal and metastableboron rich phase, B25C is codeposited with boroncarbide.129 Patterned deposits can be obtained by directwriting process, in which a pattern of thin linesdeposited on the substrate by moving the substrateperpendicular to the axis of the laser beam. Fibredepositions are also possible by moving away thesubstrate parallel to the laser beam axis at a rate equalto the deposition rate of the fibre. Direct writing andfibre growth methods can be combined to produce three-dimensional structures.148

Plasma enhanced CVD

In PECVD chemical reaction takes place after thecreation of plasma of reacting gases. The plasma isgenerally created by radio frequency (ac) or dc dischargebetween two electrodes, the space between which is filledwith the reacting gases. The necessary energy for thechemical reaction is not introduced by heating the wholereaction chamber but just by heated gas or plasma. Thedeposition takes place at lower temperature as comparedto traditional CVD. Since the formation of the reactiveand energetic species in the gas phase occurs by collisionin the gas phase, the substrate can be maintained at alow temperature. Hence, film formation can occur onsubstrates at a lower temperature than is possible in theconventional CVD process, which is a major advantageof PECVD.149

Plasma enhanced CVD has been used by manyresearchers for the fabrication of boron carbide (B-C)diodes which could accurately detect single neutrons,giving very high efficiencies. These diodes have beenused to fabricate the first real time, solid state neutrondetectors which are more efficient and reliable than anyother neutron detecting semiconductor reported todate.150 Lee et al.25,151 have fabricated photoactive p-nhetrojunction diode by PECVD of boron carbide thinfilms from nido-pentaborane (B5H9) and methane(CH4)on Si (111). A B5C/Si(111) hetrojunction diode by asynchrotron radiation induced decomposition of ortho-carborane fabricated by Byun et al.152 has been found tobe comparable with PECVD diodes. Hwang et al.153

have successfully fabricated and tested a boron carbide/boron diode on aluminium substrates and a boroncarbide/boron junction field affect transistor.Robertson et al.154 have fabricated real time solidstate neutron detector by PECVD using closo-1,2-dicarbadodecaborane. Adenwalla et al.155 have reportedthe fabrication and characterisation of boron carbide/silicon carbide hetrojunction diodes by PECVD. Theliterature is abundant on various possible combinations



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of source, method of fabrication, uses, etc. and only afew examples are given above.

Hot filament CVD

Hot filament CVD is an attractive technique due to itssimple design and its amenability to fundamental

chemical kinetic modelling in understanding the processchemistry. Hot filament CVD systems are based onthermal catalytic cracking of the precursors on thesurface of a high temperature filament usually rangingfrom 1000 to 2500uC. The substrate materials are usuallyheated by radiation from the hot filament and the

Table 4 Charge composition, processing conditions and product quality on vapour phase synthesis of boron carbide*

Serialno. Process Reactants Process parameters Product quality Ref. (year)

1 Vapour phasereaction

BCl3zCH4 1900uC; vacuum:5 mm of Hg

Boron carbide crystals 114 (1967)


B2H6zC2H2 Exothermic reactionand needs to beignited only by sparkplug

Amor. porous boroncarbide powder ofsubmicrometre size

117 (1977)


B2O3zCH4 1075uC, 18 h Whiskers length:0.5–4 inch; diameter:0.05–0.25 mm

115 (1970)


BCl3zCH4zH2 1650uC, 5 h; vacuumcatalyst: VCl4

Whiskers length: 50 mm;diameter: 10 mm

116 (1969)

5 RF plasmaassisted synthesis

BCl3zCH4zH2 Ar plasma Submicrometre size powder 118 (1975)

6 CVD BCl3zCH4zH2 1350uC; Sub.: carbonfibre

Crystalline B4C coating 130 (1996)

7 CVD BCl3zCH4zH2 1127–1227uC; Sub.:boron coated Mo,vacuum

Metastable phases, highlystrained microstructure

131,132 (1989)

8 CVD BCl3zCCl4zH2 1550uC, 4–5 h, Sub.:graphite

Pure long crystalline B4C;hardness: 41¡2.7 GPa

133 (1965)

9 CVD BCl3zC3H8zH2 850–1000uC, 3–6 h;Sub.: graphite cloth;vacuum: 15–25 torr

Amor. coating 134 (1981)

10 CVD BCl3zCH4zH2 1300uC,6 h; Sub.:graphite; vacuum:10 mm of Hg

B4C coating 135 (1968)

11 CVD BCl3zCH4zH2 1300uC, 3 h; Sub.:tungsten, graphite

B4C coating (B: 74 to 76%)specific gravity of 2.32 gm cm23

136 (1974)

12 CVD BCl3zCH4zH2 800–1050uC, vacuum Amor. boron carbide 137 (2006)13 CVD BCl3zCH4zH2 1000–1400uC; Sub.:

tungstenCrystalline B4C 124 (2006)

14 Laser CVD BCl3zCH4zH2 Laser: CO2; Sub.:fused silica; Ar pressure:atmospheric

Crystalline B4C 128 (1999)

15 Laser CVD BCl3zCH4zH2 Laser: CO2; Sub.:fused silica

Crystalline B4C 138 (1996)

16 Laser CVD BCl3zCH4/C2H4zH2

Laser: CO2 Ultra fine and crystalline B4C 139 (1990)

17 Laser CVD BCl3zC2H4 Laser: CO2; Sub.: fusedsilica, Ar

Adherent, crystalline B4C,15–22%C

127 (2002)

18 Laser CVD BCl3zCH4zH2 Laser: CO2; Sub.: fusedsilica,

Crystalline B4C and B25C 129 (1997)

19 Pulsed laserinduced CVD

C6H6zBCl3 Nd:YAG laser 14 to 33 nm B4C crystalsencapsulated in graphite

140 (1999)

20 Plasma enhancedCVD

C2B10H12

(orthocarborane)1100–1200uC; Sub.:Si (100)

B4C nanowires diameter:18–150 nm; length: 13 mm

141 (1999)

21 Microwave plasmaassisted CVD

BBr3zCH4zH2 500–600uC; Sub.:graphite

Amor. boron carbide largecomposition range (0 to40 at.-%C

142 (1990)

22 Supersonic plasmajet CVD

BCl3zCH4 500–600uC; Sub.: Si(100), ArzH2

Microcrystalline film hardness:22–32 GPa

143 (1998)

23 Thermal CVD BCl3zCH4zH2 1600uC, 3–6 h BCl3:6–15 mL min21; CH4:2–5 mL min21; H2:500 mL min21

Various composition betweenB4C and B13C2

144 (1992)

24 Hot wall CVD BCl3zCH4zH2 1000 to 1400uC; Sub.:graphite, vacuum

Crystalline B13C2, long columnargrains

145 (1998)

25 Hot filament activatedCVD

BCl3zCH4zH2 2100uC (filament)450uC (substrate);Sub.: Si (100), vacuum

Amor. boron carbide, high purityand good adhesion

146 (1994)

26 Electron beamevaporation

BzC Room temperature;Sub.: Si (100)

Thin films of crystalline boroncarbide

147 (2008)

*CVD: chemical vapour deposition; Sub.: substrate; Amor.: amorphous; RF: radio frequency.



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substrate surface temperature is usually ,500uC.146 Thedeposition is carried out under high vacuum conditionsto avoid oxygen contamination of the boron carbidephase. Deshpande et al.146 have obtained adhesivecoating of boron carbide on silicon substrate and thewear resistance of the coated surface was found to beextremely high when tested using a WC/Co ball as thepin.

Vapour phase synthesis methods are suitable for thinfilm coating of boron carbide and preparation of finepowder, fibres, whiskers, etc. However the powdersproduced by this process are generally non-stoichiometric and not suitable for fabrication of denseproducts. These methods are best suited for laboratorystudies.

Synthesis from polymer precursorsAs an alternative to high temperature reaction techni-ques, there is great interest in development of polymerprecursors to produce ceramic materials at lower tem-peratures. Some of the boron loaded organic com-pounds such as carborane (C2BnHnz2), triphenylborane,polyvinyl pentaborane and borazines on pyrolysis yieldB4C. Generally this process is carried out in the tem-perature range 1000–1500uC in vacuum or inert atmo-sphere. A US patent156 describes a process for making afree flowing boron carbide powder from boric acid andsugar. The mixture dissolved in ethylene glycol is driedin air at 180uC and then heated in hydrogen at 700uC.This reaction product is ground and fired at 1700uC for7 h to yield fine boron carbide powder. Mondal et al.157

describe a low temperature synthetic route in which apolymeric precursor is synthesised by the reaction ofboric acid and polyvinyl alcohol, which on pyrolysis at400/800uC gives crystalline boron carbide. Sinha et al.158

have presented a process in which, a stable gel is formedfrom aqueous solution of boric acid and citric acid. Thisgel is further processed to yield a precursor which onheating under vacuum to 1450uC produces B4C.Economy et al.159 have prepared boron carbide fibre

by heating ‘amine treated B2O3 fibre’ in inert atmo-sphere at 2000–2350uC. Cihangir et al.160 have devel-oped a method based on sulphuric acid dehydration ofsugar to synthesise a precursor material which onheating to temperature between 1400 and 1600uCyields crystallised B4C and B4C/SiC composites.Table 5156–159,161–167 gives the comparative summary ofstudies reported on the synthesis of B4C using polymerprecursors.

Liquid phase reactionSynthesis of ultra fine boron carbide powder using liquidprecursors has been attempted by a few. This method isalso known as solvothermal process or coreductionmethod. Unlike conventional methods, this can beoperated at much lower temperatures to yield boroncarbide of desired properties. Shi et al.168 have studiedthe formation of ultra fine boron carbide powders bycoreduction of boron tri bromide and carbon tetra-chloride using sodium as reducing agent as per thefollowing reaction

4BBr3zCCl4z16Na?B4Cz4NaClz12NaBr (16)

The reaction was carried out in an autoclave at 450uC.B4C crystals obtained were composed of uniformspherical (80 nm dia) and rod-like (200 nm diameterand 2?5 mm long) particles (Fig. 8).168 Gu et al.169 haveobserved the formation of nanocrystalline B4C bysolvothermal reduction of CCl4 using lithium inpresence of amorphous boron powder in an autoclaveat 600uC.

4BzCCl4z4Li?B4Cz4LiCl (17)

Hexagonal B4C crystals with a particle size of approxi-mately 15–40 nm diameters were obtained.

Ion beam synthesisBoron carbide thin films can be grown by directdeposition of Bz and Cz ions. In this process,parameters such as ion energy, ion flux ratio of different

Table 5 Charge composition, processing conditions and product quality on synthesis of boron carbide using polymerprecursor

Serialno. Polymer precursors

Temperature,uC Atmosphere

Holdingtime, h Product quality Ref. (year)

1 Polyvinyl borate 1300 Argon 5 Crystalline 161 (2009)2 Reaction product of H3BO3

and citric acid1500 Vacuum 2.5 Crystalline, micrometre

sized, free carbon: 2.38%162 (2006)

3 Reaction product of H3BO3

and polyvinyl alcohol400–800 Air 3 Crystalline (orthorhombic),

boric acid as impurity157 (2005)

4 Reaction product of H3BO3

and citric acid1450 Vacuum 2 Crystalline, free carbon

11.1 wt-%158 (2002)

5 Solution product of H3BO3

and glucose1400 … … B/C composite containing

crystalline B4C163 (2002)

6 Condensation product of H3BO3

and 2-hydroxy benzyl alcohol (HBA)1500 Ar 4 Crystalline 164 (1999)

7 Polyvinyl pentaborane 1000 Ar 8 Amorphous, black andshiny

165 (1988)

1450 Ar 48 crystalline 165 (1988)8 Condensation product of H3BO3

and 1,2,3 propanetriol1400 Ar 2 Crystalline 166 (1985)

9 Ethyl Decaborane (C2H5B10H13) 1215 Vacuum ,1 Crystalline B4C coating(0.005 inch) on tungstenwire

167 (1969)

10 Solution product of H3BO3, sugarand ethylene glycol

1700 H2 … Crystalline B4C powder 156 (1975)

11 Amine treated B2O3 fibre 2000–2350 Inert atmosphere … Boron carbide fibre 159 (1974)



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Ltd ion species and the substrate temperature, which can be

independently controlled, could be advantageously usedfor obtaining the preferred composition and nature ofthe boron carbide film. Ronning et al.170 have grownthin film of boron carbide (BxC) by direct ion beamdeposition on silicon using an ion energy of 100 eV atroom temperature. Todorovic et al.171 have observed theformation of amorphous boron carbide (BxC) bybombardment of Bz and B3z ions on fullerene. Beamenergies were in the range of 15 keV for Bz to 45 keVfor B3z and fluences were between 261014 and261016 cm22.

Vapour liquid solid (VLS) growthBoron carbide whiskers can be grown by carbothermalVLS growth mechanism. This mechanism involves thetransport of boron and carbon as gas phase species to aliquid catalyst metal (Fe, Ni or Co) in which whiskerconstituents get dissolved. When the catalyst becomessupersaturated with boron and carbon, boron carbidewhiskers precipitate out of the metal droplets. Carlssonet al.172 have prepared B4C whiskers and platelets usingthis technique. B2O3 and carbon black were used assource of boron and carbon respectively. NaCl and Cowere added to facilitate the growth of whiskers. B2O3

reacts with NaCl to form BCl, which along with carbondissolve in liquid cobalt and then precipitate as boroncarbide whiskers. Rao et al.173 have studied theformation of boron carbide whiskers using K2CO3 andNiCl2 as a low melting liquid and catalyst to enhance theformation of B4C whiskers and platelets. An et al.174

have used gallium oxide and sodium chloride to prepareboron carbide nanobelts having a length of around 1 to10 mm and thickness of around 80 to 150 nm, which isshown in Fig. 9.174 Ma et al.175 have investigated thegrowth of boron carbide nanowires by the addition ofiron to the precursor mixture containing carbon, boronand boron trioxide. This resulted in reduction ofdiameter of nanowires from 50–200 nm to 10–30 nm.Scanning electron micrograph of the nanowires is shownin Fig. 10.175 A comparative study of various methodsof boron carbide synthesis is presented in Table 6.

Some of the attempts to produce boron carbidecannot fall into any of the classifications discussed

above. Thakkar et al.176 have synthesised high purityultra fine boron carbide powders by reacting B2O3 withmethane in a non transferred arc dc thermal plasmareactor. A recent article177 explains the process ofmaking boron carbide–carbon eutectic containing39 wt-%C by melting B2CN in graphite crucible at2600uC.

Boron carbide powder is either utilised directly orconsolidated to dense bodies. Various methods ofdensification, the mechanisms involved and the productquality are discussed in the following pages. Densi-fication techniques can be broadly classified as pressure-less sintering and pressurised sintering. Atmospheric/reaction/microwave and thermal plasma sintering aretermed as pressureless sintering techniques. The nuancesof densification of powder compacts, complexity and thereasons for incomplete densification by pressurelesssintering are discussed in detail by Lange.178

Pressurised sintering can be classified as solid and gascompaction methods. Solid compaction methods are hot

8 Image (TEM) of B4C rod-like particles (200 nm diameter

and 2?5 mm long) prepared at 450uC by sodium reduc-

tion of BBr3 and CCl4:168 reprinted with permission

from Elsevier, Solid State Commun., 2003, 128,

Fig. 3(c) in p. 7

9 Boron carbide nanobelts prepared by VLS growth from

charge of boron oxide, activated carbon, gallium oxide

and sodium chloride at 1400uC:174 reprinted with per-

mission from Trans. Tech. Publications, Key Eng.

Mater., 2007, 336–338, (III), Fig. 1 in p. 2167

10 Boron carbide nanowires prepared by VLS growth

with help of iron addition:175 reprinted with permission

from American Chemical Society, Chem. Mater., 2002,

14, Fig. 5(b) in p. 4405



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pressing, spark plasma sintering and super high pressuresintering. Gas compaction methods are hot isostaticpressing and high pressure gas reaction sintering.

Densification of boron carbideIn spite of its high temperature strength, application ofB4C is rather limited, in real life, due to difficulties indensification, low fracture toughness and low oxidationresistance beyond 1000uC. Consolidation of B4C iscomplicated due to its high melting point, low self-diffusion coefficient and high vapour pressure. Very highsintering temperatures are required for densification dueto the presence of predominantly covalent bonds in B4C.Boron carbide particles generally have a thin coating ofsurface oxide layer which hinders the densificationsprocess. At temperatures ,2000uC, surface diffusionand evaporation condensation mechanism occur, whichresults in mass transfer without densification. Densi-fication is achieved only at temperatures .2000uC, bygrain boundary and volume diffusion mechanisms. Athigher temperature exaggerated grain growth also takesplace resulting in poor mechanical properties. One moreobservation at temperatures .2150uC is volatilisation ofnon-stoichiometric boron carbide, leaving minute car-bon behind at the grain boundaries.

Dole et al.179 have observed the microstructure of B4Ccompacts fired above 2000uC to be highly porousinterconnected structure with clusters of grains con-nected by small neck like regions and separated by large,channelled porosity. Grabchuk et al.180–182 have foundthat shrinkage starts at 1500uC, recrystallisation above1800uC and rapid grain growth above 2200uC. Attemperatures above 2250uC, the sintered body contains,5% residual porosity. Lee et al.183,184 have observedthe start of densification at 1800uC, rapid increase in

densification 1870–2010uC and a slow down in densifi-cation rate 2010–2140uC. The surge in densification1870–2010uC is attributed to the presence of oxide layerwhich helps in precipitation of B4C through liquid B2O3

or due to evaporation and condensation of rapidlyevolving oxide gases (BO and CO). Slower densificationat temperatures above 2010uC is attributed to evapora-tion and condensation of B4C. Figure 11183 shows thechanges in weight, dimension and grain size whilesintering of boron carbide.

Densification of boron carbide without deteriorationof mechanical properties can be achieved either by usinga suitable sintering aid and/or applying the externalpressure (e.g. hot pressing, hot isostatic pressing).Selection of the additive and the method of consolida-tion are generally dictated by the end use of the productand the properties that are required. The additive byitself or due to in situ reaction with boron carbide wouldform a non volatile second phase aiding in densificationand property enhancement. Hence, selection of theadditive should be directed towards the formation of asuitable structure providing the correct properties foruse. Recent or advanced techniques such as microwave/spark plasma sintering, explosive compaction, etc. helpto obtain dense products without microstructuralcoarsening. These techniques are presently limited tolaboratory scale only. Detailed literature survey onpressureless sintering with or without sintering aids, hotpressing, hot isostatic pressing, spark plasma andmicrowave sintering of boron carbide are presented inthe following sessions.

Pressureless sinteringPressureless sintering is a simple and economic processto produce dense compacts. This operation is carried outin two steps. In the first step green compacts with

Table 6 Comparison of boron carbide synthesis methods*

Method Boron source Carbon source Advantage Disadvantage

Carbothermic reduction H3BO3 or B2O3 PC, graphite,activated carbon

Cheap raw material,suitable for commercialproduction

High boron losses,obtained in lump form,need grinding for powderproduction

Magnesiothermic reduction B2O3 or Na2B4O7 PC, graphite,activated carbon

Fine powder, exothermicreaction, suitable for SHSprocess

Product contaminatedwith Mg, MgB2

Synthesis from elements Boron PC, graphite,activated carbon

No loss of boron, goodcontrol over purity andcarbon content of product

High cost of elementalboron

Vapour phase synthesis BCl3, BBr3, BI3,B6H6, B2O3

CH4, C2H4, C2H6,C2H2, CCl4

Suitable for thin films, finepowder, fibers, whiskers

Difficult to produce B4Cpowder suitable fordensification, not amenablefor large scale production

Synthesis from polymerprecursors

Boric acid, B2O3,polyvinyl pentaborane,polyvinyl borate, ethyldecaborane

Polyvinyl alcohol,citric acid, hydroxylbenzyl alcohol,sugar, ethyleneglycol

Low temperature process High free carbon content,still in laboratory stage

Liquid phase reaction BBr3, boron CCl4 Low temperature process,suitable for nanoparticles

Need of reactive metalsuch as Na or Li, newmethod of synthesis

Ion beam synthesis Boron Carbon Suitable for BxC Only for thin films, ofacademic interest only

Vapour liquid solid growth B2O3 Carbon black Suitable for whisker Need of molten metalcatalyst, of academicinterest only

*PC: petroleum coke; SHS: self-propagating high temperature synthesis.



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sufficient handling strength are prepared by uniaxial diecompaction. These green pellets are then fired at chosenhigh temperatures in controlled atmosphere. A recentlydeveloped new technique, combustion driven compactprocess, yields much higher green density and strengththan the normal die compaction.185 In this process, highpressure generated by ignition of a combustion gasmixture which raises the pressure in the chamberdramatically in a very short period of time and pushesdown the top ram on the powder at an extremely highspeed realising the compaction.

Sintering of B4C powder compacts is commonlyperformed in an inert gas medium. But the applicationof vacuum helps in evaporation of the surface oxidelayer and also prevents further oxidation, there bypromoting the sintering mechanisms. Removal of theoxide layer by heating in a reducing atmosphere beforesintering also has a similar effect. Literature data onpressureless sintering of boron carbide and the productevaluation are presented in Table 7.179,183,186–204

Increase in particle surface area (9 to 17 m2 g21) andsintering temperature (2100 to 2190uC) give higherdensities (56 to 71% TD).187 Densities of .90% TDare achieved by sintering at a temperature of .2200uCwith particles close to or ,1 mm size. Grain coarseningis the common feature in compacts with high densitiesobtained by pressureless sintering.191,193 Microstructuresof samples with 87 and 93% TD, obtained by pressure-less sintering of 0?8 mm median diameter powders at2300 and 2375uC are presented in Fig. 12.193 Grain sizesare in the range 40–100 mm indicating large graingrowth. Surface to surface mass transport which isactive at temperatures below which densification canproceed is responsible for the coarsening process. Athigher temperatures, vapour phase diffusion of boroncarbide is the important transport mechanism forcoarsening. Rapid heating is helpful in achieving higherdensities with fine microstructure, as the compacts canbe heated to a temperature where densification can takeplace before the microstructure becomes highly coar-sened.179,183,188,205 Appearance of twins in the grains ischaracteristic of boron carbide. These twins slowly

vanish during high temperature annealing. Vickershardness and flexural strength of the pressurelesssintered boron carbide samples are in the range 18–24 GPa and 120–200 MPa respectively, which are lowerthan theoretical values. One can conclude that, withpure B4C, a densification .90% TD is possible only atvery high sintering temperatures of y2300uC. Suchcompacts have a coarse grained microstructure of

11 Sintering of boron carbide compact: change in weight, dimension, grain size and coefficient of thermal expansion up

to 2300uC:183 reprinted with permission from Wiley-Blackwell, J. Am. Ceram. Soc., 2003, 86, (9), Fig. 8 in p. 1472

12 Microstructure of pressureless sintered boron carbide

(0?8 mm) at a 2300uC and b 2375uC showing grains in

range 40–100 mm indicating large grain growth:193 rep-

rinted with permission from Elsevier, Ceram. Int.,

2006, 32, Fig. 2(b) and (g) in p. 230–231



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Ta

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7P

ow

de

rd

eta

ils

,s

inte

rin

gp

ara

me

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an

dc

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ss

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hard

ness,

GP

aK

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am

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xu

ral

str

en

gth

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Ref.

(year)

1B

4C

FC

:2–4. 9

;D

505

2. 0

to10. 5

2170

to2230uC

,15

min

,A

r94. 0

–95. 6

12. 0

–25. 5

2. 9

1–3. 1

9160–180

186

(1988)

2B

4C

Sta

rck

make

B/C

53. 7

to3. 8

;D

505

0. 8

;S

S:

15–20

2190uC

,1

h,

Ar

(up

to2000uC

invacuum

)94–95

……

……

188

(2004)

3B

4C

2250uC

65%

Coars

e…

……

179

(1989)

B4C

D505

12300uC

70–72%

Coars

eB

4C

z6

wt-

%C

SS

:12

2300uC

.95%

Fin

e4

B4C

D50(

12150uC

,15

min

,A

r78

B4C

:6

……

…189

(1981)

B4C

z3

wt-

%C

(phenolic

resin

)S

S:

22

96

B4C

:4

3. 2

353

5B

4C

D50,

52175uC

,15

min

,A

r…

B4C

:105

190

(1987)

B4C

z(p

oly

carb

osila

nez

phenolic

resin

510%

)S

S:

10. 5

95

B4C

:28

B/C

:4. 3

2S

iC:

,3

6B

4C

D50(

0. 8

42250uC

91. 3

–92. 7

B4C

:2. 5

8–

3. 1

1…

……

183

(2003)

B4C

z3

wt-

%C

(phenolic

resin

)S

S:

18. 8

2250uC

98. 4

–98. 6

B4C

:2. 2

6–2. 4

……

…B

/C5

3. 7

67

B4C

2200uC

,1

h78. 6

B4C

:28

174

191

(2003)

B4C

2250uC

,1

h82. 5

B4C

:50

…B

4C

z3

wt-

%C

SS

:2. 5

32250uC

,1

h92

B4C

:13

350

B4C

z5

wt-

%C

2250uC

,1

h93

…B

4C

z7. 5

wt-

%C

2250uC

,1

h89

…B

4C

z9

wt-

%C

2250uC

,1

h86

…8

B4C

D50<

32250uC

,2

h,A

r95. 5

19–21

……

192

(2005)

B4C

z4%

CS

S:

18. 8

;O

:1. 2

3%

;N

:0. 4

%2250uC

,2

h,

Ar

97. 7

19–21

……

B4C

z4%

BC

arb

on

bla

ck:

D505

20

nm

;S

S:

120

2250uC

,2

h,A

r87. 0

18–20

……

B4C

z4%

SiC

SiC

(SS

):11. 5

92250uC

,2

h,

Ar

90. 8

19–23

……

B4C

z4%

TiB

2TiB

2:

D90<

42250uC

,2

h,

Ar

95. 4

21–25

9B

4C

2375uC

,1

h,

vacuum

93

B4C

:50–120

24–25

……

193

(2006)

B4C

z1

wt-

%C

D505

0. 5

to2

2325uC

,1

h,

vacuum

91

B4C

:y

20

B4C

z3

wt-

%C

(Acheson)

2325uC

,1

h,

vacuum

90

B4C

:y

10

B4C

z5

wt-

%Z

rO2

B:

78%

;C

:19. 0

5%

;O

:0. 5

%2275uC

,1

h,

vacuum

93

B4C

:y

532

B4C

z5

wt-

%TiB

22375uC

,1

h,

vacuum

82

B4C

:y

15

10

B4C

D505

1. 3

32150uC

,vacuum

86

B4C

:30

22

2. 2

220

213

(2008)

B4C

z5

wt-

%TiB

2S

S:

6. 6

490

…26

2. 6

260

B4C

z10

wt-

%TiB

2B

/C5

3. 8

to3. 9

93

B4C

:17

29

2. 8

290

B4C

z15

wt-

%TiB

296

…31

2. 8

5360

B4C

z20

wt-

%TiB

296

B4C

:14

29

2. 9

320

B4C

z25

wt-

%TiB

298

…26

3. 0

5280

B4C

z30

wt-

%TiB

298. 5

B4C

:10

23

3. 4

270



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Seri

al

no

.M

ate

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co

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ion

,w

t-%

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Ref.

(year)

11

B4C

2050uC

,1

h,

inert

74

18

1. 9

195

(2006)

B4C

D505

1. 3

32150uC

,1

h,

inert

78

21

2. 0

B4C

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wt-

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S:

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42150uC

,1

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82

22

2. 1

B4C

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wt-

%ta

lcB

/C5

3. 8

to3. 9

2150uC

,1

h,

inert

85

23

2. 2

B4C

z15

wt-

%ta

lcTalc

:26. 6

2%

Al 2

O3,

47. 7

8%

SiO

2,

25. 6

%M

gO

2150uC

,1

h,

inert

90

25

2. 3

B4C

z20

wt-

%ta

lc2150uC

,1

h,

inert

92

26

2. 4

B4C

z25

wt-

%ta

lc2150uC

,1

h,

inert

95

27

2. 6

B4C

z30

wt-

%ta

lc2150uC

,1

h,

inert

98

23

2. 7

12

B4C

2275uC

,1

h,

vacuum

86. 6

3B

4C

26. 8

5221

(2008)

B4C

z2. 5

wt-

%Z

rO2

B4C

:D

50<

189. 5

6B

4C

,Z

rB2

…B

4C

z5

wt-

%Z

rO2

B/C

54. 0

993. 8

6B

4C

,Z

rB2

31. 6

8B

4C

z10

wt-

%Z

rO2

ZrO

2re

acto

rg

rad

e95. 3

B4C

,Z

rB2

31. 1

8B

4C

z15

wt-

%Z

rO2

95. 5

B4C

,Z

rB2

30. 1

9B

4C

z20

wt-

%Z

rO2

93. 0

8B

4C

,Z

rB2

30. 9

5B

4C

z25

wt-

%Z

rO2

95. 8

2B

4C

,Z

rB2

31. 7

1B

4C

z30

wt-

%Z

rO2

92. 3

4B

4C

,Z

rB2

31. 0

7B

4C

,Z

rB2

13

B4C

2050uC

,1

h,

Ar

72

19

2. 0

190

196

(2006)

B4C

2150uC

,1

h,

Ar

75

22

2. 1

200

B4C

z5

wt-

%Z

rO2

D505

12150uC

,1

h,

Ar

79

25

2. 2

205

B4C

z10

wt-

%Z

rO2

SS

:14

2150uC

,1

h,

Ar

86

27

2. 6

210

B4C

z15

wt-

%Z

rO2

ZrO

2z

3w

t-%

Y2O

32150uC

,1

h,

Ar

97

28

2. 9

220

B4C

z20

wt-

%Z

rO2

D505

0. 8

2150uC

,1

h,

Ar

97

29

3. 0

235

B4C

z25

wt-

%Z

rO2

SS

:16

2150uC

,1

h,

Ar

97

27

3. 0

260

B4C

z30

wt-

%Z

rO2

2150uC

,1

h,

Ar

98

26

3. 1

340

14

B4C

2190uC

,1

h,

Ar

62

50

197

(1999)

B4C

z5

wt-

%Ti

2190uC

,1

h,

Ar

67

…B

4C

z10

wt-

%Ti

2190uC

,1

h,

Ar

73

…B

4C

z15

wt-

%Ti

D50

,1

2190uC

,1

h,

Ar

78

…B

4C

z20

wt-

%Ti

SS

:9–17

2190uC

,1

h,

Ar

86

…TiO

2:

D50,

2(u

pto

1500uC

:vacuum

)…

B4C

z5

wt-

%TiO

22160uC

,1

h,

Ar

72

B4C

:10

200

B4C

z10

wt-

%TiO

22160uC

,1

h,

Ar

77

TiB

2:

5–7

300

B4C

z15

wt-

%TiO

22160uC

,1

h,

Ar

88

350

B4C

z20

wt-

%TiO

22160uC

,1

h,

Ar

95

420

15

B4C

2190uC

,1

h,

Ar

(up

to1500uC

:vacuum

)71

120

187

(2000)

B4C

z10

wt-

%TiO

2D

505

5to

773

B4C

:10

200

B4C

z20

wt-

%TiO

2S

S:

17

75

TiB

2:

5300

B4C

z30

wt-

%TiO

2TiO

2:

D100(

280

330

B4C

z40

wt-

%TiO

293

400

Ta

ble

7C

on

tin

ue

d



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Seri

al

no

.M

ate

rial

co

mp

osit

ion

,w

t-%

Sta

rtin

gp

ow

der

deta

ilsP

rocessin

gco

nd

itio

ns

Sin

tere

dd

en

sit

yr

th,

%M

icro

str

uctu

re,

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Vic

kers

hard

ness,

GP

aK

IC,

MP

am

1/2

Fle

xu

ral

str

en

gth

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Pa

Ref.

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16

B4C

z0

to30

wt-

%TiO

2z

1to

6w

t-%

CB

4C

:D

505

0. 6

39

1900–2050uC

,1

h,

Ar

Up

to99%

B4C

:22¡

2…

3. 2

–3. 7

1350–513

216

(1996)

SS

:19. 8

TiB

2:

6–10

Purity

:99. 8

9%

TiO

2and

C:

sub

mic

rom

etr

e17

B4C

D505

1. 6

(B/C

53. 9

)2180uC

,2

h,

Ar

83

……

198

(2007)

B4C

z22

vol.-%

ZrO

2O

2:

1. 7

%98

27–31

350

B4C

z28

vol.-%

TiO

2Z

rO2:

sub

mic

rom

etr

e98

28–33

375

B4C

z8

vol.-%

Y2O

3TiO

2:

sub

mic

rom

etr

e97. 5

27–30

180

Y2O

3:

sub

mic

rom

etr

e18

B4C

2150uC

,15

min

,A

r85

B4C

:3. 6

3199

(1992)

B4C

z1

wt-

%A

l 2O

3D

50<

0. 9

(B/C

53. 9

)92

B4C

:5. 3

5B

4C

z2

wt-

%A

l 2O

3(1

wt-

%O

2and

0. 4

%N

2)

93

B4C

z3

wt-

%A

l 2O

3A

l 2O

3:

99. 9

9%

pure

96

B4C

:7. 0

7B

4C

z4

wt-

%A

l 2O

388

B4C

z5

wt-

%A

l 2O

386

B4C

:8. 9

219

B4C

z1. 5

%TiC

D100:

sub

mic

rom

etr

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h,

Ar

96. 3

B4C

:12,

TiB

24. 0

286

200

(1998)

B4C

z1. 5

%TiC

SS

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,2

h,

Ar

94. 9

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266

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B4C

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TiC

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505

1. 5

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h,

Ar

98. 4

B4C

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TiB

2,

C28

O:

0. 5

3%

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:0. 1

0%

20

B4C

D505

0. 0

82260uC

,15

min

,A

r–N

271. 9

201

(1977)

B4C

z1. 0

wt-

%B

eC

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:16. 1

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,15

min

,A

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280. 1

B4C

z1. 0

wt-

%B

eC

B/C

:3. 5

72230uC

,15

min

,A

r–N

285. 5

B4C

z1. 0

wt-

%B

eC

BeC

:sub

mic

rom

etr

e2280uC

,15

min

,A

r–N

294. 0

21

B4C

z10

wt-

%S

iCz

3w

t-%

Al

B4C

:D

505

9;

SiC

:D

505

2. 5

2150uC

,10

min

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202

(1982)

22

B4C

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wt-

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,1

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2. 6

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203,

204

(2002,

2002)

B4C

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5. 8

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y50 mm, high amount of intragranular porosity andpoor flexural strength (y200 MPa).

Carbon as sinter additive

Various sinter additives have been tested to increase therate of densification, control grain growth and improvemechanical properties of boron carbide. Carbon hasbeen found to be very effective, primarily in reducing theoxide layer of the boron carbide powders, there bypromoting sintering and hindering grain growth.Carbon, well distributed between the particles reactswith B2O3 coating according to the reaction

2B2O3z6C?B4Cz6CO (18)

Removal of oxide layer allows direct contact betweenB4C particles, permitting sintering to initiate at sig-nificantly lower temperature (y1350uC). In addition,carbon at the grain boundaries enhances diffusion,facilitating accelerated solid state sintering. Varioustypes of carbon such as petroleum coke, carbon black,graphite, glucose and phenolic resin (e.g. phenolformaldehyde) can be used as sintering aid. If carbonin solid form such as coke, graphite or carbon black ischosen, it is mandatory that very fine size is used and themixing carried out thoroughly, in mixtures such asplanetary mill/attritor to form an intimate contact suchas a fine coating on boron carbide particles. An additivesuch as phenol formaldehyde resin plays two roles;namely as binder while cold pressing and as carbonprecursor which is uniformly distributed on the surfaceof the grains. Any carbon which is not consumed by thereduction reaction is left in the compact as excesscarbon. High densities of 98?65% TD with a fine grainsize of 2?34 mm have been achieved by the addition of3%C in the form of phenolic resin.183 Compactsexhibiting a finer, less faceted grain structure withsmaller and more uniformly distributed pores wereprepared by the addition of 6 wt-%C (in the form of athermoset resin).179 Carbon addition inhibits the coar-sening process, thereby preventing the formation oflarge unsinterable pores. As a result, carbon doped B4C

undergoes normal sintering and nearly full density canbe achieved. Much of the carbon remains in the B4Cmicrostructure as graphite particle. Phenolic resin ascarbon addition is found better than carbon black andglucose.191 With 3 and 5 wt-%C the density obtainedwas 92 and 93% TD respectively. With higher amountsof carbon (>7?5%C), a reversal in densification wasobserved. Yin et al.206 have studied the sintering kineticsof pure and carbon doped boron carbide with 0?42 mmsized B4C powders in the temperature range 1900–2200uC and a period of 5–45 min. They have deduced,the main sintering mechanisms to be volume and grainboundary diffusion for pure boron carbide and grainboundary diffusion for carbon doped boron carbideshowing activated sintering. Schwetz et al.189,207 haveobtained compacts of 97–98% TD with the addition of1–3% phenolic type of carbon using a powder of largesurface area (22 m2 g21). A fine grained (7–8 mm)compact with superior mechanical properties (flexuralstrength: 351–353 MPa and fracture toughness:3?3 MPa m1/2) was obtained.

Very fine powders in the range of nanosizes wouldincrease the rate of sintering due to very large surfacearea and particle to particle contact. Zorzi et al.192 haveused carbon black of 20 nm size (specific surface area:120 m2 g21) with boron carbide powder of surfacearea18?8 m2 g21 to obtain 97?7% TD compacts havingKnoop hardness in the range 19–21 GPa by sintering at2250uC for 2 h. While studying the densificationbehaviour of nanosized boron carbide, it has beenfound that solid state sintering (1500 to 1850uC) startsonly after the evaporation of B2O3. The formation ofeutectic (B4C-C) liquid droplets appears on the surfaceof graphite coated B4C particles above 1920uC, whichform the weaker regions in the sintered product.208

Sample sintered at 2300uC, showed the grain boundaryto be free from carbon and the excess carbon present asfine graphite crystals at the triple point resulting inexcellent mechanical properties (Fig. 13a).209 Highresolution TEM image of the sample shows noboundary or amorphous layer (Fig. 13b).209 Large,

13 a TEM image of pressureless sintered boron carbide with 7?9 wt-% phenolic resin at 2250uC showing graphite crystal

at triple points and b high resolution TEM image of grain boundary of same sample:209 reprinted with permission

from the Ceramic Society of Japan, J. Ceram. Soc. Jpn, 2004, 112, (5), Figs. 2 and 3 in p. S400



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complex boron carbide shapes of density .94% arefabricated by slip casting method using a binder andsintering at 2280uC for 2 h.210

Thermosetting phenolic types of resins are mostsuitable as carbon precursors as they give a completeuniform coating of carbon on the surface of carbideparticles. Carbon can be replaced by boron to react withsurface oxide layer of B4C to achieve similar effects. Inaddition boron will also react with free carbon of B4C toform carbide.192

Addition of a small amount (3–5 wt-%) of carbon toB4C plays an important role in eliminating the surfaceoxide layer, thereby achieving higher densities (y97%TD) with fine grains and improved mechanical proper-ties (hardness: 19–25 GPa; flexural strength: 160–350 MPa). The quantity and the method of carbonaddition have to be carefully chosen to avoid free carbonin the sintered body.

Role of carbide/boride additives

In addition to carbon, other grain refinement agents forB4C are Si and Al. Although the strength can be signi-ficantly improved by grain size reduction, the toughnessremains low. Addition of carbides and borides have beenfound to increase the flexural strength and fracturetoughness of B4C by grain refinement and crack pro-pagation influencing mechanisms such as crack deflec-tion, micro crack interaction and crack impediment.211

Carbides/borides can either be directly added or formedby in situ reaction with B4C while sintering. Faberand Evans212 have predicted that fracture toughnessincreases due to crack deflection around second phaseparticles in two-phase ceramic materials. The idealsecond phase, in addition to maintaining chemicalcompatibility, should be present in amounts of 10 to20 vol.-%. Greater amounts may diminish the toughnessincrease due to overlapping particles. Particles with highaspect ratios are most suitable for maximum tougheningespecially particles with rod shaped morphologies.

Zorzi et al.192 have reported that addition of4 wt-%TiB2 to B4C lead to good results in final density,hardness and wear resistance. Baharvandi andHadian213 have reported the addition of TiB2 onsinterability and mechanical properties of B4C. Densityand fracture toughness values were found to increasewith TiB2 fraction in the entire range of 0 to 30%,whereas bending strength and hardness improve tocertain amount (15%TiB2) and then start decreasing.With 30%TiB2 the highest density and fracture tough-ness of 98?5% TD and 3?4 MPa m1/2 were achievedrespectively. At 15%TiB2 the highest hardness of 31 GPaand flexural strength of 360 MPa were obtained. TiB2

also acted as a grain growth inhibitor. TiB2 is formed byreaction sintering of boron carbide with titanium oxideat y1500uC as per the following reaction

B4Cz2TiO2z3C?2TiB2z4CO: (19)

Levin et al.197 have found that TiO2 is reduced bycarbon originated from the carbide phase. This leads tothe formation of substoichiometric boron carbide, whichis responsible for increased rate of sintering. Addition of40 wt-%TiO2 to B4C powder (17 m2 g21 specific area)gives a compact of 95% TD after sintering for 1 h at2160uC.187,197 Presence of TiB2 results in lowering ofactivation energy for sintering and hence very high

densities of 99% could be achieved without pressure attemperatures of 2050–2100uC.214,215 Metallographicexamination revealed a two phase microstructure withB4C grains of 10 and TiB2 of 5–7 mm size. Grain sizeof B4C was found inversely proportional to the quantityof carbon in the sample. Increase in volume fraction ofTiB2 led to an increase in flexural strength and fracturetoughness to a maximum of 513 MPa and 3?7 MPa m1/2

respectively at 15 vol.-%.216,217 The observed increase instrength and fracture toughness are due to the interac-tion between the propagating crack front and localthermal mismatch stress associated with TiB2 particles.

Titanium carbide also reacts with boron carbide toform TiB2 as per the reaction

B4Cz2TiC?3Cz2TiB2 (20)

The amount of second phase TiB2 and excess carbonplay a distinct role in sintering. Densities higher than95% TD were obtained by sintering at temperaturesabove 2150uC.200 As the carbon content increased from1?5 to 6?0%, the grain size of B4C decreased from 10 to3 mm, flexural strength increased from 292 to 502 MPa,and toughness decreased from 4?2 to 2?9 MPa m1/2.

Addition of various transition metal (Ti, Zr, Hf, V,Nb and Ta) carbides/borides for preparing dense boroncarbide pellets have been patented.218,219 Boron carbideis reacted at approximately 1500uC with the transitionmetal oxide/carbide to form a mixture of boroncarbidezmetallic carbide/boride, which is sintered attemperatures .2000uC to obtain densities .95%.Goldstein et al.198 have studied the reaction betweenB4C and MeO mixtures (MeO–TiO2, ZrO2, V2O5,Cr2O3, Y2O3 and La2O3) fired up to 2180uC for 2 h inargon. The main solid reaction products are found to beborides. Such composites exhibited a sintering aptitudehigher than that of monolithic B4C, increasing with theamount of metal oxide in the initial mixture. Thehardness and strength of composite were comparable tothat of hot pressed B4C. Khazai et al.220 have patented aprocess for the preparation of boron carbide/titaniumdiboride composite with uniform distribution of both.

Baharvandi et al.196 have studied the effect of additionof Yttria doped zirconia on sintering behaviour(between 2050 and 2150uC in argon for 1 h) andmechanical properties of B4C. Densities of 97% TDwere obtained in samples with >15%ZrO2 addition.Boron carbide reacts with ZrO2 during sintering to formZrB2 as per the following reaction

B4Cz2ZrO2?2ZrB2zB2O3zCO: (21)

Fracture toughness and flexural strength of the com-pacts increased from 2?1 to 3?1 MPa m1/2 and 200 to340 MPa respectively with the increase of ZrO2 contentfrom 0 to 30%. Processing in vacuum and highertemperature (2275uC) increased the hardness to.30 GPa.221 Figure 14 presents the variation in hard-ness of pressureless sintered B4C with ZrO2 addition.Hardness in the entire range of composite is y30 GPacompared to 27 GPa for pure B4C. Backscattered imageof this sample shows a white phase containing up to1?2%Zr distributed in B4C matrix (Fig. 15).Fractography (Fig. 16)221 shows the mode of fractureto be a combination of transgranular and intergranular.

The in situ reactions for the formation of carbide/boride consume some of the carbon from boron carbide,



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thereby generating substoichiometric boron carbide.This defective structure enhances diffusion kineticsthereby improving the rate of sintering. The improvedmechanical properties are attributed to the presence offine distribution of secondary phase particles in thematrix. If the second phase is not as hard as boroncarbide and then presence of large volume is likely todeteriorate the mechanical properties and hence one hasto optimise the level of second phase addition to obtainthe best properties.

Liquid phase sintering

Liquid phase sintering is carried out either by theaddition of a substance with low melting point or by theformation of a low melting substance by in situ reactionof the additive with boron carbide. Wettability, capillaryaction, dissolution and reprecipitation are the importantparameters, which decide the ability to sinter and themechanical properties. Wetting of polycrystalline B4Cby molten aluminium between 900 and 1200uC havebeen studies by Lin et al.222 They found the Wettabilityof B4C to be strongly depend on temperature and theformation of different reaction products such asAl2?1B51C8, Al3BC, AlB2, Al3B48C2 at the interface.

Danny et al.223 have studied the problems of B4C–Alparticulate composite fabrication and explained thatchemical reactions between B4C and aluminium occurbetween 800 and 1400uC much faster than capillaryinduced liquid rearrangement, inhibiting the densifica-tion process. It is suggested that the application ofexternal pressure during sintering to accelerate densifi-cation faster than the kinetics of phase formation.Attempts have been recently made to prepare B4C–CeB6/Al composite with improved strength and tough-ness by pressureless infiltration technology.224

Silicon with a melting point of 1410uC, when added toboron carbide acts as a liquid sinter additive and inaddition reacts with carbon of boron carbide to formsilicon carbide, thus helping the sintering process andalso strengthening the matrix. Silicon carbide hasattractive properties, similar to that of boron carbidesuch as high hardness (28 GPa), low specific gravity(3?1 g cm23) and good wear resistance and henceconsidered an attractive sinter addition to boroncarbide. Taylor et al.225 describe a process where siliconis infiltrated into a porous body of boron carbide andthen sintered in the temperature range 1500–2200uC toobtain dense (2?57 g cm23) non-porous boron carbidebody which is extremely hard (modulus of rupture235 MPa, modulus of elasticity 353 GPa). X-ray dif-fraction pattern obtained correspond to normal B4C,second boron carbide type having an expanded lattice,alpha and beta silicon carbides and silicon. The chemicalanalysis showed 16?5%C, 32?6% total silicon, 50?9%total boron, 0?16% free carbon and 12?6% free Si. Thepresence of unreacted, free silicon lowers mechanicalproperties of reaction bonded B4C. The fraction of freeSi can be reduced by increasing the green density of theinitial boron carbide preforms.226 Mallick et al.227 havedemonstrated the possibility of net shape production viainfiltration of Si melt into porous preform containingB4C and carbon. Chen et al.228 have studied theformation and sintering mechanisms of reaction bondedsilicon carbide boron carbide composites. In the productsintered at 1450uC, a non-stoichiometric boron carbide

14 Variation in hardness of pressureless sintered B4C

with ZrO2 addition (hardness in entire range of com-

posite is y30 GPa compared to 27 GPa for pure

B4C):221 reprinted with permission from Elsevier,

Ceram. Int., 2008, 34, Fig. 3 in p. 1545

15 Backscattered image of sintered boron carbide with

ZrO2: white regions analysed to contain 1?2%Zr

16 Image (SEM) of fractured surface of sintered boron

carbide with ZrO2 addition: mode of fracture seen as

combination of trans- and intergranular:221 reprinted

with permission from Elsevier, Ceram. Int., 2008, 34,

Fig. 6 in p. 1547



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phase B12(C,Si,B)3 and a minor phase rich in B10C orB49C1?82 were seen. Microcracks were also observed inboron carbide grains. B4C cermets, for application asneutron absorber have been prepared by sintering with aeutectic alloy of Al–Si at a low temperature of 550uC.229

The role of iron in the sinterability of B4C has beenstudied by contact angle measurement and dilatometricdensification. The interaction zone consisted of a finemixture of FeB and graphite. The sintering kineticsconfirmed the liquid phase sintering leading to improvedmass transfer.230 Mizrahi et al.231 have also attributedthe formation of liquid phase promoting the masstransfer mechanism in B4C–Fe mixtures. Iron additionsalso provide the desired porosity for successful infiltra-tion of preforms.

Addition of carbon to react with infiltrated silicon forforming silicon carbide rather than with boron carbide isbeneficial as silicon carbide has a lower hardness andhigher specific gravity compared to boron carbide.232

Hayun et al.233 have found that presence of a largefraction of plate-like SiC in samples formed due to initialhigher porosity, are responsible for increased flexuralstrength and fracture toughness on account of strength-ening effect of the high aspect ratio of the second phaseparticles. The dynamic strength and the dynamicfracture toughness K1d are significantly higher than thecorresponding static properties and are insensitive to theresidual silicon fraction and to the strain rate (up to5103 s21). Properties of the B4C material prepared bythis method are given as: density, 2?57 g cm23; young’smodulus, 382 GPa; flexural strength, 278 MPa andfracture toughness, 5?0 MPa m1/2. Organosilicon poly-mers such as polycarbosilane,190 polysiloxanes, poly-silazanes, polysilanes, metallopolysiloxanes andmetallopolysilanes,234 which upon pyrolysis yield SiCand free carbon have been found to be very effective inpressureless sintering of boron carbide. Weaver202 haspatented a process where in a mixture of boron carbideand silicon carbide are mixed in an aluminium mill to acomposition of 87B4C–10SiC–3Al which is sintered at1800–2300uC to densities up to 94% TD.

Chromium boride forms a eutectic liquid phase withB4C at a temperature of 2150uC. The fractured surfaceof the B4C specimen with 20 mol.-%CrB2 prepared at2000uC showed the CrB2 particles to be partiallymelted and wetted with the adjacent B4C particles(Fig. 17).203,204,235 There was no significant growth ofB4C grains and the densification was mainly attributedto B4C particles rearrangement caused by the CrB2–B4Ceutectic liquid formation. However at temperaturesabove 2200uC, abnormal grain growth of B4C occurred.Specimen with 98?1% TD (20 mol.-%CrB2, sintered at2030uC) showed a high flexural strength of 525 MPa anda moderate fracture toughness of 3?7 MPa m1/2. Theimprovement in fracture toughness is due to theformation of microcracks and the deflection of propa-gating cracks due to the thermal mismatch of CrB2 andB4C.

Addition of alumina improves the densification ofboron carbide with the formation of liquid phaseAlB12C2 by the reaction between B4C and Al2O3.Maximum density of 96% TD was achieved by theaddition of 3 wt-% alumina doped B4C sintered at2150uC for 15 min.199 Exaggerated grain growth wasobserved in the specimen containing .4% alumina.

Baharvandi et al.195 have studied the effect of highalumina talc (26?62Al2O3–47?78SiO2–25?6MgO) powderas a sintering aid. The sample sintered at 2050uC for 1 hshowed the formation of MgB2, SiC and Al2O3. Themechanism of sintering is due to the formation of liquidphase anstatite at 2000uC and its reaction with B4C toform SiC, MgB2 and Al2O3. Though the density (78–98%) and fracture toughness (2–2?8 MPa m1/2) of thecompact increased with the quantity of talc in the chargeup to 30%, microhardness attained a peak value of26 GPa at 25% and then fell down.

A US patent236 explains a process wherein boroncarbide powder is mixed with aqueous sodium silicate(to give SiO2 equivalent of 0?75–1?5 wt-%B4C) andalumina (1–3 wt-%), compacted and sintered at 2100uCto give compacts exceeding 90% TD. As per another USpatent by Prochazka201 addition of 0?5–3 wt-%BeC toboron carbide helps in achieving a density of 85–94%TD by sintering at 2200–2280uC. Weaver in his patent202

has mentioned a process to obtain refractory bodiescomposed of 60–98 wt-% boron carbide, 2–40 wt-%silicon carbide and 0–10 wt-% aluminium with densitiesexceeding 94% TD by cold pressing followed by apressureless heat treatment.

Low melting metals/alloys such as Al and Al–Si havebeen used to bind boron carbide particles to differentshapes for neutron absorber applications. Liquid phasesintering of boron carbide is carried out by in situreaction with alumina, silica, BeC, CrB2, etc. Thisreduces the sintering temperature by a few hundreddegrees and the sintered product has a fine microstruc-ture and moderate mechanical properties. Silicon isfound to be an excellent additive which is introducedinto a sintered porous body of B4C by infiltrationtechnique. This helps in two ways: by liquid phasesintering and by SiC formation which greatly improvesthe mechanical properties. Owing to fine grain structureand high fracture toughness of the end product, this isthe method chosen for the manufacture of B4C basedarmour shields.

Hot pressingIn conventional sintering, the rate of densification isvery slow. Though higher densification can be achievedat higher temperatures, it is difficult to prevent grain

17 Fracture surface of B4C–CrB2 specimen indicating

partially melted CrB2:204 reprinted with permission

from Springer, J. Mater. Sci. Lett., 2002, 21, Fig. 4 in

p. 1446



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growth. Addition of second phase can only retard butnot completely prevent the grain growth. Pressureassisted consolidation/sintering generally involves heat-ing a powder compact, with the simultaneous applica-tion of pressure. The powder compacts are typicallyheated externally using graphite heating elements andthe pressure is applied hydraulically. A photograph of avacuum hot press with front door open showing thegraphite die and heaters is presented in Fig. 18. Hotpressing is the most common method for fabricatingdense articles of pure B4C. Without sinter additives B4Ccan be fully densified by hot pressing .2100uC with anapplied load of >30 MPa. Photographs of boroncarbide pellets of various sizes compacted by hotpressing are presented in Fig. 19. Densification bysintering during hot pressing results from three succes-sive mechanisms:

(i) particle rearrangement, where the total and openporosities decrease and the closed porosity remainsconstant (temperature range: 1800–1950uC)

(ii) plastic flow, leading to the closing of openporosity without significantly affecting the closedpores (1950–2100uC)

(iii) volume diffusion and pore elimination at the endof the hot pressing (2100–2200uC).1,186,237–239

The density, porosity and microstructure of hot pressedB4C depend on the hot pressing parameters, such astemperature, pressure, time, heating/cooling rate, etc.Though very fine particles are not a precondition, thesize of boron carbide used for hot pressing generally fallsin the range 1–10 mm. Table 8179,194,234,239–258 presentsthe literature data on hot pressing of boron carbide with/without additives.

The density of the compacts obtained under identicalhot pressing conditions (2150uC for 10 min) were 91?6

and 99?7% TD with starting powders of 3?85 and0?35 mm respectively.259 Though at lower temperatures,heating rate influences the rate of densification, attemperatures .2000uC it has no important influence ondensification.240 A temperature of >2100uC and apressure of 34?4 MPa are necessary to obtain densityclose to 100% TD. Slow cooling after densification hasbeen found to be responsible for reduction in the finaldensity due to the formation of pores while cooling. Asboron carbide reacts with the die material, inner liningof the graphite die is essential to prevent this reaction.BN lining has been found to be most suitable. Themicrostructure of hot pressed specimens show no graingrowth (1?5–2?0 mm) up to 1950uC, a steady even growthup to 2050uC (the final grain size 5 mm) and an unevensized growth and the presence of large number of twinsat 2150–2200uC.239 Fast heating rates and application ofhigh pressure (40 MPa) have been helpful in obtainingfull densification at a lower temperature of 1900uC.179

Samples obtained under these conditions show amicrostructure, free of grain boundary phases, with anaverage grain size of 2 mm and faceted submicrometrepores accounting for ,1 vol.-% porosity. Jianxin250 hasprepared boron carbide nozzles by hot pressing at2150uC in an inert atmosphere with a pressure of36 MPa using starting powders of ,3 mm size with adensity, hardness, fracture toughness and flexuralstrength of 95?5% TD, 32?5 GPa, 2?5–3?0 MPa m1/2

and 300–400 MPa respectively. He has also studied theerosion wear of this by abrasive air jets using SiO2, SiCand Al2O3 powders. While studying the densification byhot pressing, Ostapenko et al.239 have found that thedensification of boron carbide is controlled by a processleading to non-linear creep, whose rate is a function ofthe square of stress. Experimenting on the activatedsintering kinetics by the addition of iron, Koval’chenkoet al.238 have noted that, dislocation climb is the mainmechanism leading to creep; whose rate is a quadraticfunction of stress. Properties of dense B4C compactsprepared by hot pressing generally have the bestproperties with the following values:260 hardness, 29–35 GPa; fracture toughness, 2?8–2?9 MPa m1/2; elasticmodulus, 450–470 GPa; thermal conductivity, 30–42 W m21 K21; coefficient of thermal expansion,

18 Vacuum hot press with front door open showing gra-

phite heaters and insulation

19 Boron carbide pellets of various sizes compacted by

hot pressing



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:1. 4

%34. 4

MP

a,

2. 7

ks,

heating

rate

:330

Kks

21;

coolin

gra

te:

1665

Kks

21

1775

K65. 1

6. 0

……

…240

(1983)

D505

2. 9

1975

K72. 4

7. 0

SS

:0. 2

4–6. 2

2175

K80. 2

12. 1

2325

K98. 5

13. 5

2375

K98. 4

15. 2

2475

K99. 6

16. 4

2B

4C

D505

1. 5

synth

esis

from

the

ele

ments

2200uC

,22

MP

a,

10

min

98

.5,

ala

rge

num

ber

of

twin

s…

……

239

(1979)

3B

4C

D505

1;

SS

:12

2100uC

,40

MP

a,

30

min

,A

r.

95

2–3

……

…179

(1989)

4B

4C

D50,

32150uC

,36

MP

a,

60

min

95. 5

4–8

32. 5

2. 5

–3. 0

300–400

250

(2005)

5bB

zC

D505

2. 0

;S

S:

1. 2

71950uC

,30

MP

a87

……

……

241

(2000)

Am

orp

hous

Bz

CD

505

0. 2

;S

S:

12. 7

61800uC

,30

MP

a99

aBz

CD

505

2. 7

4;

SS

:0. 8

91800uC

,30

MP

a91

6B

4C

B4C

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505

10;

O:

0. 1

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wt-

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MP

a,

1h,

HR

:0. 5

Ks

21,

CR

:1. 7

Ks

21

2. 5

gcc

21

10–50

240

242

(1979)

B4C

z5%

BB

:D

505

20

2. 4

9g

cc

21

…190

B4C

z15%

B2. 4

2g

cc

21

10–40

200

7B

4C

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2z

CB

4C

:D

505

0. 5

0;

SS

:21. 5

2000uC

,50

MP

a,

1h,

Ar

100

B4C

:3. 8

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2…

3. 1

870

243

(2005)

TiO

2:

D50,

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505

0. 4

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SS

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100

B4C

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B4C

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815

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zTiO

2z

C2100uC

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MP

a,

8m

in.

95

0%

TiB

227

3. 1

200

257

(1990)

5%

TiB

230

4. 0

350

10%

TiB

232

5. 0

500

20%

TiB

234

5. 1

630

30%

TiB

230

4. 6

530

40%

TiB

228

4. 3

400

9B

4C

z23. 4

%TiO

2z

5. 2

8%

carb

on

bla

ck

B4C

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505

0. 6

3;

SS

:19. 8

;TiO

299. 9

%p

ure

,sub

mic

rom

etr

e2000uC

,20

MP

a,

Ar,

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HR

:15–25uC

min

21

15

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TiB

2;

rest:

B4C

6. 1

621

244

(2000)

10

B4C

B4C

:D

505

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MP

a,

65

min

,A

r95. 0

B4C

:6–10

29

2. 5

245

246

(2002)

B4C

z10%

(W,T

i)C

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i)C

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505

1to

21850uC

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MP

a,

50

min

,A

r98. 5

1–2,

TiB

2,W

2B

528

2. 8

400

B4C

z30%

(W,T

i)C

1850uC

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MP

a,

40

min

,A

r99. 2

0. 5

–1. 5

26

3. 9

550

B4C

z50%

(W,T

i)C

1850uC

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MP

a,

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min

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r99. 5

,1

23

4. 5

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B4C

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505

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505

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MP

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65

min

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r95. 0

5–8

21

2. 6

0540

247

(2009)

B4C

z5. 3

%M

o1950uC

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MP

a,

50

min

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1–2

……

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4C

z5%

TiC

z5%

Mo

1950uC

,35

MP

a,

50

min

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r99. 1

1–2

22

3. 4

0550

B4C

z10%

TiC

z4. 7

%M

o1950uC

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MP

a,

50

min

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r99. 2

1–2

25

4. 2

5695

B4C

z15%

TiC

z4. 5

%M

o1950uC

,35

MP

a,

50

min

,A

r99. 0

1–2

24. 5

3. 7

5625

B4C

z20%

TiC

z4%

Mo

1950uC

,35

MP

a,

50

min

,A

r98. 5

1–2

23. 5

3. 6

0550



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Seri

al

no

.M

ate

rial

co

mp

osit

ion

,w

t-%

Sta

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gp

ow

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deta

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pre

ssin

gco

nd

itio

ns

Sin

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dd

en

sit

yr

th,

%M

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str

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hard

ness,

GP

a

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tati

on

tou

gh

ness,

MP

am

1/2

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xu

ral

str

en

gth

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Pa

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ren

ce

(year)

12

B4C

:29. 5

–57%

;B

:18. 3

–35. 5

%;

Si:

3. 8

–7. 5

%;

WC

z

TiC

:0–45. 3

%;

Co:

0–2. 8

%

D50,

166

MP

a,

3m

in,

heating

rate

:40

Km

in2

1;

coolin

gra

te:

100

Km

in2

1

1620uC

3. 5

gcc

21

B4C

–TiB

2–W

2B

512

…550

245

(1986)

1670uC

3. 6

gcc

21

26

620

1720uC

3. 5

9g

cc

21

30

710

1820uC

3. 5

gcc

21

28

830

1920uC

3. 4

5g

cc

21

25

710

2120uC

3. 2

gcc

21

26

580

13

B4C

B4C

:D

505

0. 4

3;

SS

:15. 3

;O

2:

2w

t-%

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140

pp

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Al:

50

pp

m2050uC

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MP

a,

1h,

Ar

79. 3

Eute

ctic

liquid

of

CrB

2z

B4C

…1. 9

180

256

(2003)

B4C

z10%

CrB

2C

rB2:

D505

3. 5

86

2. 2

350

B4C

z15%

CrB

294

2. 5

500

B4C

z20%

CrB

295

2. 8

550

B4C

z22. 5

%C

rB2

96

3. 2

620

B4C

z25%

CrB

298

3. 2

684

95

3. 2

660

14

B4C

B4C

:D

505

0. 4

31900uC

,50

MP

a,

1h,

Ar

99. 0

2. 5

675

248

(2003)

B4C

z5%

CrB

2C

rB2:

D505

3. 5

99. 6

2. 6

551

B4C

z10%

CrB

299. 7

2. 7

580

B4C

z15%

CrB

299. 0

2. 8

630

B4C

z20%

CrB

299. 0

3. 5

630

B4C

z25%

CrB

298. 6

3. 4

580

15

B4C

z50%

SiC

B/C

54. 1

;B

:D

505

1. 5

;O

:,

4%

1900uC

,30

MP

a,

30

min

,A

r;H

R:

15–150uC

min

21

2. 5

0g

cc

21

B4C

,S

iC…

……

273

(1993)

Siz

Bz

CC

,S

S:

80;

Si:

D1005

52. 7

4g

cc

21

B4C

,S

iC16

B4C

z8

to13%

silo

xane/

phenolic

2275uC

,28

MP

a,

1h,

Ar

97–99. 7

B4C

,S

iC/C

……

…234

(1996)

17

B4C

zsod

ium

sili

cate

z

mag

nesiu

mnitra

tez

Fe

3O

4

B4C

:D

505

0. 1

to1

1750uC

,24

MP

a,

10

min

to4

h45–68

…25

……

249

(1974)

45–98. 4

18

B4C

B4C

:D

505

3. 5

;B

N:

D50,

nanosiz

ed

1850uC

,30

MP

a,

1h,

N2

99. 5

B4C

,nano-h

-BN

21

5. 4

410

254

(2008)

B4C

z10

wt-

%B

N99. 2

15

6. 0

420

B4C

z20

wt-

%B

N99. 0

11

5. 2

410

B4C

z30

wt-

%B

N98. 5

85. 0

360

B4C

z40

wt-

%B

N98. 1

74. 3

310

19

B4C

z60%

Al 2

O3

B4C

:D

505

1. 0

1700uC

,35

MP

a,

1h,

Ar

3. 5

3…

28

4. 2

¡0. 7

530¡

30

258

(2005)

B4C

z70%

Al 2

O3

Al 2

O3:

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53. 0

27

4. 2

¡0. 4

560¡

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B4C

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Al 2

O3

3. 7

73. 2

23

4. 3

¡0. 5

600¡

70

B4C

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Al 2

O3

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63. 4

21

3. 5

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550¡

45

20

B4C

zA

l 2O

3(B

4C

/Al 2

O35

18

:1)

2150uC

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MP

a,

65

min

,A

r95. 5

B4C

:2–5

22. 4

¡1. 2

3. 2

¡0. 5

300¡

34

271

(2008)

B4C

zA

l 2O

3z

5%

TiC

B4C

:D

505

3to

5,

.95%

1950uC

,35

MP

a,

60

min

,A

r98. 7

B4C

,TiB

224. 1

¡1. 1

4. 1

¡0. 5

430¡

31

B4C

zA

l 2O

3z

10%

TiC

Al 2

O3:

D505

1to

2,

.99%

1950uC

,35

MP

a,

60

min

,A

r98. 9

B4C

:0. 5

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¡1. 0

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¡0. 4

445¡

30

B4C

zA

l 2O

3z

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TiC

:D

505

1to

2,

.99%

1950uC

,35

MP

a,

60

min

,A

r98. 7

B4C

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224. 3

¡1. 0

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¡0. 4

386¡

29

B4C

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l 2O

3z

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TiC

1950uC

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MP

a,

60

min

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r98. 5

B4C

,TiB

223. 2

¡1. 0

4. 2

¡0. 4

323¡

32

Ta

ble

8C

on

tin

ue

d



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561026 K21; flexural strength, 350 MPa; compressivestrength, 1400–3400 MPa.

Fractography of fully dense boron carbide compact isshown in Fig. 20.193 The mode of fracture appears to betransgranular.

Fabrication of boron carbide shapes by hot pressingthe mixture of particulate boron and carbon is alsopractised.111 Kalandadze et al.241 compacted boron andcarbon powders in ampoules up to 30% TD, by shockcompression, as a result of an explosive detonation.These pellets were densified by hot pressing at tempera-tures 1900–2100uC and pressures 20–40 MPa in boronnitride lined graphite moulds. A comparison between a-rhombohedral, b-rhombohedral, and amorphous boronindicated that sintering into the b-rhombohedral phaseat the final stage can give higher densities as follows:BbRBaRBamorphous, which is attributed to the phasetransformation occurrence from amorphous boron to b-rhombohedral boron through a-rhombohedral boronmodification.

Compacts with densities higher than that achievableby pressureless sintering process are produced by hotpressing of boron carbide powders. The added advan-tages of hot pressed compacts are fine grained structure,very low porosity and improved mechanical properties.Larger size powders in the range 3–10 mm can besintered to near theoretical densities by hot pressing aty2000uC and 30–40 MPa pressure. For applicationsuch as in nuclear industry, where pure boron carbide isessential and impurities/additives cannot be tolerated,hot pressing is the preferred method to produce dense,pure compacts.

Role of sinter additives

Earlier we have seen that carbon additive greatlyenhances the sintering kinetics in pressureless sintering.Such an effect is not expected in the case of hot pressingas the sintering mechanisms are different. In theliterature also one does not find any report on hotpressing of B4C with carbon addition. However additionof boron would consume the free carbon available in theboron carbide. It is seen that small additions of B (1 to5%) improves the strength of boron carbide specimens atS

eri

al

no

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co

mp

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ion

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t-%

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en

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yr

th,

%M

icro

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ness,

GP

a

Ind

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on

tou

gh

ness,

MP

am

1/2

Fle

xu

ral

str

en

gth

,M

Pa

Refe

ren

ce

(year)

21

B4C

z6%

La

2O

3z

12%

Al 2

O3z

12%

C…

1850uC

,20

MP

a,

1h,

vacuum

92. 5

B4C

,A

l 8B

4C

7,

LaA

lO3,

97

HR

A…

156. 7

6251

(2008)

22

90

to99%

B4C

z0

to1%

BN

/AlN

zre

st

RE

oxid

e-A

l 2O

3

B/C

53. 8

to4. 5

;D

505

0. 7

to3. 0

1825–2000uC

,10. 3

MP

a,

Ar

99. 6

–100

B4C

:1–2

25–27

3. 0

–3. 9

700–800

252

(2007)

23

B4C

z30%

Al

B4C

:2

60

mesh

600,

16. 3

MP

a,

40

min

1. 7

5g

cc

21

……

……

194

(1978)

Al:

2325

mesh

24

B4C

/Cu

578

:22

B4C

:D

505

5to

40;

Cu:

D505

1to

81050uC

,39

MP

a,

1h

81. 9

……

……

253

(1999)

B4C

/Cu

592

:873. 6

*FC

:fr

ee

carb

on

inB

4C

;H

R:

heating

rate

;C

R:

coolin

gra

te;

D50:

mean

part

icle

dia

mete

r,mm

;S

S:

sp

ecific

surf

ace

are

a,

m2

g2

1;

RE

:ra

reeart

h.

Ta

ble

8C

on

tin

ue

d

20 Microstructure of hot pressed boron carbide showing

transgranular fracture:193 reprinted with permission

from Elsevier, Ceram. Int., 2006, 32, Fig. 4(a) in p. 232



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lower hot pressing temperatures.242 Similar to prepara-tion of boron carbide based cermets for nuclearapplications boron carbide rings with adequate strengthhave been prepared by hot pressing technique withy30 wt-% aluminium as binder for possible use asneutron absorber.194 A high density B4C/Cu cermet with70 vol.-%B4C exhibiting high thermal conductivity hasbeen prepared by hot pressing of Cu coated B4Cpowders for the application of absorber materials inliquid metal cooled fast breeder reactor.253 Thoughboron carbide in various forms is used in nuclearindustry, literature data on the production methods isscarce. An US patent261 explains a process for producingB4C armour plates with improved ballistic properties bythe addition of Cr, B, or mixtures thereof.

Role of TiB2

Reaction sintering of boron carbide with the addition oftitanium oxide and carbon as per reaction (19) producesextremely fine high surface area particles of TiB2 whichpromote densification and limit the grain growth of theboron carbide matrix. This microstructure with TiB2

particles uniformly distributed in a fine grained B4Cmatrix is responsible for the increase in fracturetoughness and strength. B4C–15 vol.-%TiB2 compositewith a flexural strength of 621 MPa and fracturetoughness of 6?1 MPa m1/2 have been prepared by hotpressing at 2000uC and a pressure of 20 MPa in argonatmosphere for 1 h by Skorokhod et al.244 They haveobserved that factors for the increased strength are dueto the healing of the cracks during sintering and thepresence of TiB2 particle which force the crack topropagate in a non-planar fashion thus enhancing theenergy dissipation at the crack tip. An US patent243

explains a process to prepare boron carbide compositescontaining 5 to 30 mol.-% titanium diboride with veryhigh flexural strength (870 MPa) and fracture toughness(3?4 MPa m1/2). Addition of Fe in small amounts (0?5%)has been found to be effective in increasing the finaldensities of B4C–TiB2 composite due to the formation ofFe–Ti rich liquid phase at the grain junctions.262

Role of mixed borides

As seen in the previous lines addition of TiO2 hasbrought down the hot pressing temperature of B4C by>100uC. Further attempts to reduce the sintering tem-perature without compromising the strength are givenbelow. Reaction sintering of B4C with 30 wt-%(W,Ti)Cat 1850uC for 30 min showed increase in fracturetoughness and flexural strength up to 50 wt-%(W,Ti)Ccontent. Fine grains of (0?5–2 mm) TiB2 and W2B5 wereseen in the microstructure. The sintering temperature ofthis composite is 300uC lower than that of monolithicB4C. Flexural strength and fracture toughness forcomposite with 40 to 50% additive were 700 MPa and4?5 MPa m1/2. The increase in fracture toughness isattributed to the residual stresses generated by differ-ences in the thermal expansion coefficient between B4C,TiB2 and W2B5. The effect of TiB2/W2B5 on the path ofcrack and deflection in the composite is shown inFig. 21.246 Further reduction in sintering temperaturewas achieved by the addition of B, Si and Co to theabove referred mixture. Reaction sintering of B4C withWC, TiC, B, Si and Co by attrition milling followed byhot pressing at 1720uC for 2 h gave a compact with threedistinct phases of B4C, W2B5, and TiB2, hardness in the

range 28–33 GPa and flexural strength of 830 MPamax.245 US patent by Petzow et al.263 describes a processfor the preparation of boron carbide/transition metalboride moulded articles comprising of B4C, Si, WC and/or TiC and Co by hot pressing between 1550 and1850uC. Effect of variation of TiC addition on hotpressing of B4C/TiB2/Mo composite has been studied byJianxin et al.247 and the maximum values of fracturetoughness, flexural strength and hardness reported are4?3 MPa m1/2, 695 MPa and 25?0 GPa respectively.During ball milling/mixing of B4C with additives, thepowders get contaminated and the microstructure of thecomposite appears very complicated after hot pressingdue to the diffusion of W, Co, Ni, Cr, etc. either into theTiB2 grains to form (Ti,M)B2 or (Ti,M)B2 coated grains,and Ti, Fe, Co, Ni, and Cr into W2B5 to form boron richboride or the interfacial layer.264

Role of carbides/nitrides

Li et al.265 have prepared a composite containing B4C,SiC, TiB2 and BN by reactive hot pressing of B4C,Si3N4, a-SiC and TiC powders and the hardness,bending strength, fracture toughness and relative densityof the composite were 88?6 HRA, 554 MPa,5?6 MPa m1/2 and 95?6% respectively. Microstructureanalysis showed the presence of laminated structure anda clubbed frame dispersion phase and bunchy dispersionphase among the matrix. Fractography and crackpropagation suggested that crack deflection and brid-ging are the possible toughening mechanisms.

Han et al.266 have synthesised a high strength (400–570 MPa, 6–9?5 MPa m1/2) B4C–TiB2–SiC–graphitecomposite by reactive hot pressing using B4C, TiC andSiC powders. The crack deflection at the phaseboundary between B4C matrix and dispersions consist-ing of SiC and TiB2, which occur by residual stresses dueto the differences in thermal expansion coefficients ofB4C, TiB2 and SiC while cooling from the fabricationtemperature is responsible for the enhanced fracturetoughness values. Similar very high strength material(four point bend strength: 850 MPa; fracture toughness:6?1 MPa m1/2) has been prepared by the addition of5–30 vol.-%Mo to B4C/(W,Mo)B2 by hot pressing at1900uC.267 Fractography of this sample showing thecrack propagation path is depicted in Fig. 22.267 When

21 Crack path produced by Vickers indentation on

polished surface of hot pressed B4C–30 wt-%(W,Ti)C

composite:246 reprinted with permission from Elsevier,

Ceram. Int., 2002, 28, Fig. 10 in p. 429



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boron is added to the above mixture, hardness of thecompact increases due to the inhibition of B4C decom-position but the bending strength and the fracturetoughness reduce.268 A composite B4C–VB2–C obtainedby reaction synthesis with hot pressing has been foundto exhibit high hardness and bending strength suitablefor application as wear and shock resistance compo-nents.269 Cr and V carbides are also found to be effectivein obtaining high densities and fine grained structure.270

A process in which a preceramic organosilicon polymerwhich on pyrolysis yields SiC and free carbon has beenpatented for preparation of dense bodies of boroncarbide (.97% TD) by hot pressing in inert atmosphereat a temperature of 2275uC and a pressure of 28 MPa.234

Reaction sintering of boron carbide with the additionof oxides/carbides/nitrides has been successfullyemployed to obtain a microstructure of fine particlesof reaction product (borides/carbides/nitrides) in B4Cmatrix. These additions lower the sintering temperaturethan that of monolithic B4C. Flexural strength andfracture toughness of these composites are very high dueto the residual stresses generated by differences in thethermal expansion coefficient between B4C and reactionproducts, crack bridging and deflection mechanisms atthe interface, etc. Small quantities of B, Si, Ti, Fe, Co,Ni, Cr, W, etc. either intentionally added or accidentallyacquired during the grinding/mixing operations are alsofound to be effective in marginally reducing the sinteringtemperature and improving the flexural strength/fracturetoughness due to the formation of complex boridephases and multi interfaces.

Liquid phase sintering

Addition of CrB2 aids in lowering the hot pressingtemperature due to the formation of CrB2–B4C eutecticat 2150uC. B4C–20 mol.-%CrB2 composite fabricatedby hot pressing at 1900uC shows a high strength of630 MPa and a modest fracture toughness of3?5 MPa m1/2. The very fine grained microstructure isresponsible for high flexural strength and residualstresses caused by thermal expansion mismatch ofCrB2 and B4C for increasing toughness.243,248,256

Similarly addition of Al2O3 enhances the sinteringkinetics of boron carbide due to a liquid phaseformation at 1950uC.249 Jianxin and Junlong271 havestudied the effect of TiC content on the micro-structure, mechanical properties and sand erosion rate

of B4C/Al2O3/TiC composites. Addition of TiCincreased the hardness of the composite and thehardness had direct influence on the erosion rate of thenozzles. The addition of rare earth (RE) oxides such asY2O3, La2O3 reduces the sintering temperature due tothe formation of a liquid phase near the yttrium–aluminate composition (60 wt-%Y2O3–40 wt-%Al2O3,melting point 1870uC).251 Pore free sintered boroncarbide materials with high strength (700–800 MPa)and fracture toughness (3?6–3?9 MPa m1/2) have beenprepared by low pressure hot pressing with the additionof BN/AlN and oxide binder (RE oxide–Al2O3).252

Additives such as CrB2, Al2O3, Y2O3, La2O3 etc. bringdown the sintering temperature of B4C due to liquidphase formation. The reaction products formed areboride of the respective oxide, which enhances themechanical properties. Addition of TiC with otheroxides increases the hardness and erosion resistance ofB4C composite.

A number of new processing methods are envisaged toproduce materials with designed structure and proper-ties. A machinable B4C/BN nanocompoisite has beenfabricated by hot pressing microsized B4C particlescoated with amorphous nanosized BN particles.254 Thehardness of composite decreased with increase contentof BN while the machinability improved significantly. Acomposite with .20 wt-%BN content exhibited excel-lent machinability.272 The surface hardness and wearresistance of this composite has been improved bysilicon infiltration process.255 Combination of SHS tech-nique with hot pressing (called combustion hot pressing)has been used to prepare a composite, containing B4Cand SiC formed by reaction among Si, B and C, in theform of interlocked matrices with very low porosity anduniform microstructure.273 Graded porosity B4C mate-rials can be produced by a layering approach usingdifferent size distributions of B4C powders in the greenstate, and then densifying the layered assembly by hotpressing at 1900uC.274 Cobalt as sinter additive has alsobeen attempted for hot pressing of boron carbidepowders with 5 wt-%TiC at temperatures ,1500uCand a high pressure of 5–6 GPa.275

Hot isostatic pressing (HIP)The HIP process, originally known as gas pressurebonding, uses the combination of elevated temperatureand high pressure to form/densify raw materials orpreformed components. The application of the pressureis carried out inside a pressure vessel, typically using aninert gas as the pressure transmitting medium with orwithout glass encapsulation of the part. A resistanceheated furnace inside the vessel is the temperaturesource. Parts are loaded into the vessel and pressurisa-tion occurs usually simultaneously with the heating. Thehigh pressure provides a driving force for materialtransport during sintering which allows the densificationto proceed at considerably lower temperature incomparison to that of traditional sintering. In addition,particularly during the initial stages of the process, thehigh pressure induces particle rearrangement and highstresses at the particle contact points. A virtually porefree product can be produced at a relatively lowtemperature. The pressure level used in the HIP processtypically is 100–300 MPa, as compared to 30–50 MPa inuniaxial hot pressing, and the isostatic mode ofapplication of pressure is generally more efficient than

22 Crack propagation path with considerable deflection

in hot pressed B4C/30W–20Mo composite:267 reprinted

with permission from Japan Society of Powder and

Powder Metallurgy, J. Jpn Soc. Powder Powder

Metall., 1999, 47, (1), Fig. 8 in p. 28



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the uniaxial one.276,277 Larsson et al.278 have studied theeffect of addition of boron, silicon and silicon carbidewhile hot Isostatic pressing boron carbide at 1850uC for1 h under a pressure of 160 MPa. Addition of boron wasfound effective in reducing the pores and graphiteinclusions and improved particle erosion resistance.Boron carbide (100% TD) could be obtained by acombination of pressureless sintering and post-HIP at2150uC for 125 min under 310 MPa of argon pres-sure.279,280 The combination of pressureless sinteringand post-HIP is gaining importance for fabrication ofdense bodies with higher densities, lower graphitecontents and significantly higher Vickers hardness thancommercially hot pressed B4C.279–281 Elimination ofresidual porosity and significant improvements inflexural strength, elastic constants and wear resistancewere observed with the addition of 1 and 3 wt-%C in theabove process.282 Fully dense and very fine grainedboron carbide has been prepared by the fabricationroute, injection moulding/pressureless sintering (2175uC)/post-HIP (200 MPa, Ar) from B4C doped with 4 wt-%carbon black.283 Near net shape with full density can beachieved by HIP.284–286 Figure 23279 shows the micro-structure of post hipped boron carbide to full theoreticaldensity. Equiaxed uniform size grains and thin grainboundary are the special features of this material withvery high hardness.279–281 A patented process explainsthe preparation of boron carbide shapes containingmetallic diborides (of Ti, Zr, Hf, V, Nb and Ta), sinteredin the temperature 2100 to 2200uC to give a density of2?47 g cc21, which on further hot isostatic pressing at2100uC under an argon pressure of 200 MPa to achievea theoretical density of 2?56 g cc21.219

Porosity severely degrades the ballistic properties ofceramic armour as it acts as a crack initiator. Sinteringaids generally degrade hardness and ballistic properties.Therefore, boron carbide protective inserts for personalarmour is hot pressed to minimise porosity (y98%relative density), yielding acceptable performance. Post-hipping of pressureless sintered boron carbide is gainingimportance for this purpose. This will not only yieldlighter weight armour but also enable forming ofcomplex shapes.

Major equipments needed for pressureless sinteringare cold compaction press and sintering furnace. For hotpressing, a graphite die is assembled between the rams of

the press and heated by the furnace surrounding it.Multi cavity dies are used for increasing the rate ofproduction. In HIP the whole equipment has to bedesigned for high temperature and high pressureoperation. This puts a limitation on the size of theequipment and the number of compacts that can befabricated at a time. Compacts produced by pressurelesssintering generally needs a finishing process of surfacegrinding and end finishing to obtain desired shape andsize. Hot pressed objects also undergo surface finishingoperations at times to remove any contamination fromthe die material. Hipped compacts do not need anyfurther processing and can be directly used.Manufacturing costs and throughput of pressurelesssintering with post-HIP are attractive compared to hotpressing.281

Spark plasma sinteringConventional pressure assisted consolidation techni-ques, such as hot pressing, hot isostatic pressing, etc.,require long processing time and high temperature inorder to produce high density parts. In order tominimise expensive machining, the powder densificationprocess must be capable of near net shaping. One suchprocess and the apparatus for rapid bonding of ceramicmaterials have been patented by Yoo et al.287 Thematerials to be consolidated are placed in a graphite dieand punch assembly. The driving force for densificationis provided by passing current directly through theparticle material, with simultaneously applying highshear and high pressure in separate steps. High shearforce in combination with pulsed electric power isinitially applied to the particle material to generateelectrical discharge that activates the particle surface byevaporation of oxide film, impurities and moisture.Subsequently bonding is accomplished by resistanceheating at the contact points between the activatedparticles in the presence of high pressure. The time andtemperature required for consolidation is lowered ashigh current density is applied in addition to high shearand high pressure (up to 2000 MPa) which leads tolocalised heating and plastic deformation at interparticlecontact areas. The rapid sintering which preferably lastsfor less than a few minutes prevents grain growth andallows the particles to retain their microstructure. Sparkplasma sintering (SPS), plasma activated sintering,plasma pressure consolidation/P2C and instrumentedpulse electrodischarge consolidation are the differentnames given for the same process.

Ghosh et al.52 have consolidated submicrometre sizedcommercial boron carbide to near theoretical densitiesusing plasma pressure compaction technique. Thedensities obtained at 1750uC by the application of88 MPa pressure in 2 and 5 min were 96 and 99?2% TDrespectively. The average grain size of these compactswas 1?6 and 2 mm. Optical micrograph (Fig. 24)52

reveals nearly equiaxed fine grained microstructure.The hardness and fracture toughness values were inthe range of 25?41 to 27?45 GPa and 3?22 to3?61 MPa m1/2 under static testing conditions.Addition of graphite and TiB2 do not aid in consolida-tion of B4C by this method. Addition of small amountsof Al2O3 and Fe has been found to be effective inachieving higher densities by SPS of B4C due toformation a liquid phase.288–290

23 B4C specimen pressureless sintered and hipped at

2150uC and 310 MPa to 99?1% relative density:279 rep-

rinted with permission from Materials Research

Society, J. Mater. Res., 2005, 20, (8), Fig. 6 in p. 2115



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In situ synthesis and densification

Influence of temperature on synthesis and consolidationhas been studied by Tamburini et al.113 Formation ofB4C commences at y1000uC and is complete by 1200uC,with a hold time of 10 min. Significant densificationoccurs above 1600uC, but the material shows evidence ofextensive crystallographic disorder due to twins whichhowever decrease at higher temperatures. Koderaet al.291 while heating B-C powders by SPS haveobserved that, formation of B4C starts at 1300uC,consolidation with twins initiates at 1600uC and 98%density obtained at 1900uC. Heian et al.106 have alsonoted similar structural defects in the material preparedby mechanical activation followed by field assistedcombustion. Wang et al.292 have noticed that B and Cbegin to react from 1300uC and the product was B richboron carbide (B4zxC) and free C. With increasingtemperature C atoms diffused into B4zxC lattice,resulting in the reduction of free carbon content anddecrease in lattice parameters of B4zxC. Densification ofthe synthesised boron carbide occurred from 1700 to1900uC. Simultaneous synthesis and densification ofB3?5C, B4C and B4?5C by spark plasma sintering hasshown that carbon free boron rich compounds areformed in the temperature range 1300–1600uC andconsolidation occurs above 1700uC.293

Fabrication of functionally graded B4C cermets

Continuous functionally graded boron carbide alumi-nium cermets have been prepared by spark plasmasintering of B4C from boron and carbon followed byinfiltration of aluminium.294 This processing routeresults in a material with very promising propertiesand interesting microstructural features. Hardness pro-file of functionally graded material before and after Almelt infiltration is shown in Fig. 25.294 A B4C/Cu gradedcomposite as plasma facing component for fusionreactors with performance better than nuclear gradegraphite has been prepared by rapid self-resistancesintering under ultra high pressure.295

Microwave processingMicrowave sintering has the advantages of uniform andrapid heating since the energy is directly coupled into thespecimen rather than being conducted into the specimen

from an external heat source. Enhanced densificationand finer microstructures, not feasible in the conven-tional furnaces are possible through the use of micro-wave systems. The sample size and shape, thedistribution of the microwave energy inside the cavity,and the magnetic field of the electromagnetic radiationare all important in heating and sintering.296 Literatureon microwave sintering of boron carbide is scarce. Oneof the recent articles describes the behaviour of B4C/SiC/Al mixtures during microwave heating in air. A densecomposite with B4C skeleton and the voids filled withthe reaction products of Al and B4C were obtained. SiCwas not attacked by oxygen and was able to contributeto matrix toughness. This material with low specificgravity and high hardness is attractive for use inlightweight armour.297 One can expect more researchusing microwave heating as and when bigger size unitswith higher power ratings become available in themarket.

A novel floating zone method has been adopted forpreparing directionally reinforced B4C–TiB2 compo-site.298 Temperature dependence of the bending strengthof this composite was evaluated in the temperaturerange 25–1600uC. With increasing temperature, its valuedecreases to 120 MPa at 800uC and then increased to230 MPa at 1000–1400uC. Even at 1600uC, the bendingstrength was as high as 200 MPa.298 The development ofnon-aqueous gel casting process for preparation of B4C–Al composites has been reported by Zhang et al.299

ConclusionsThe understanding of the crystal structure of boroncarbide has been evolving over the years and even todaycannot be said to be fully elucidated. Carbothermicreduction of boric acid has been the commercial methodfor the production of boron carbide in spite of theshortcomings. Need of the hour in carbothermic reduc-tion is process modelling, which will greatly help intuning the process to achieve improved productivity anduniform quality. Though a continuous method has beenestablished for the production of SiC,300 a similarmethod has to be adopted for B4C also. Sol–gel methodappears to be a promising technique for production ofsuitable fine boron carbide powders for direct consoli-dation. Vapour phase synthesis, still in laboratory scale,

24 Microstructure of boron carbide densified by SPS at

1750uC for 5 min, showing nearly equiaxed fine

grained microstructure:52 reprinted with permission

from Wiley-Blackwell, J. Am. Ceram. Soc., 2007, 90,

(6), Fig. 4 in p. 1853

25 Hardness versus position profile of functionally

graded boron carbide with and without Al infiltra-

tion:294 reprinted with permission from Elsevier, Mater.

Sci. Eng. A, 2008, A488, Fig. 8 in p. 337



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is an attractive process for the preparation of submicro-metre sized powders, whiskers, etc. Though thermo-dynamic models based on Gibbs free energyminimisation have been used to predict experimentalconditions, models based on mass transfer and kineticsin addition are needed to understand the depositionmechanism and the growth process. Boron carbidebased coatings by CVD methods for various semicon-ducting applications such as diode, transistor, thermo-electric converter, thermocouple, neutron sensors, etc.are gaining importance and the use of boron carbide inthis field will increase manifold in the coming years. Inaddition to the established uses, the future of boroncarbide will depend on the possible production ofmicrometre/nanosized powders, whiskers and advancedcoating techniques to meet the varying demands.

On consolidation, the research so far has been focusedon reducing the sintering temperature, inhibit graingrowth and improve the mechanical properties. Carbonhas been the chief architect of these improvements. Addi-tives based on carbides/borides/nitrides are also found tobe effective in obtaining a fine grained structure withhigher fracture toughness/flexural strength. Hot pressingand HIP have remained the main densification methodsfor production of pore free pure boron carbide due to theirability to achieve near theoretical density without graincoarsening. The process of silicon impregnation into asintered porous boron carbide body produces a very highdense compact with improved mechanical properties dueto the presence of fine SiC particles. Post-hipped pres-sureless sintering is gaining importance for manufactureof complex shapes with fine grains especially for armourmaterial. Production of nanosized particles followed bySPS for consolidation will revolutionise the method ofB4C component manufacture. The mechanism, micro-structure and properties of compacts by SPS technique areyet to be fully understood. Various available methods ofpowder production and consolidation techniques havebeen exploited for fabrication of boron carbide compo-nents with tailor made properties.

B4C to be considered as high temperature structurematerial should have good thermal and oxidationresistive properties. Detailed investigations on oxidationcharacteristics of B4C at high temperatures have beencarried out by Steinbruck et al.301,302 and others.303,304

Higher oxidation stability of B4C with the addition ofZr, Cr and W borides have also been reported by Radevet al.305 Serious efforts on oxidation prevention of boroncarbide at high temperatures and improvement ofthermal properties have not been attempted. It may beworthwhile to investigate composites with silicides andRE borides. With excellent dielectric properties, thermaland chemical stability, and erosion resistance in highintensity laser beams, BN–B4C composite materialscould find a unique place for high temperature applica-tions.306 From the point of view of application, boroncarbide has established as the material for abrasiveapplications, neutron absorber and armour material. Itsuse in electronic industry and high temperature applica-tions will see a higher growth in the coming years.

A recent study regarding road map for advancedceramics provides guide lines for future investments.307

1. Development of innovative process technologies totransfer new knowledge on functional and structuralproperties into ceramic materials and devices.

2. In the long run, usage of tailor made powders(complex composition, compositional gradient in parti-cle, well defined particle shape) and reliable usage ofnanoscale powders will become more important.

3. Techniques for near net shape forming should beconsidered a field for fruitful further activity.

All these points are truly applicable to boron carbidealso.

References1. F. Thevenot: ‘Boron carbide – a comprehensive review’, J. Eur.

Ceram. Soc., 1990, 6, 205–225.

2. M. L. Bauccio: ‘ASM engineered materials reference book’, 2nd

edn; 1994, Materials Park, OH, ASM International.

3. S. R. Murthy: ‘Elastic properties of boron carbide’, J. Mater. Sci.

Lett., 1985, 4, 603–605.

4. A. Lipp: ‘Boron carbide: production properties and application’,

Technische Rundschau, 1965, 14, 28, 33 and 1966, 7.

5. V. I. Matkovich: ‘Boron and refractory borides’; 1977,

Heidelberg/New York, Springler-Verlag Berlin.

6. D. Jianxin: ‘Erosion wear of boron carbide ceramic nozzles by

abrasive air jets’, Mater. Sci. Eng. A, 2005, A408, 227–233.

7. A. Gatti, R. Cree, J. B. Higgins and E. Feingold: ‘Boron carbide

continuous filaments’, Technical report. Jul 64–Jun 65,

Philadelphia, PA, Missile and Space Div., General electric Co.,

1965, available at: http://www.ntis.gov/

8. Y. Chen, Y. W. Chung and S. Y. Li: ‘Boron carbide and boron

carbonitride thin films as protective coatings in ultra-high density

hard disk drives’, Surf. Coat. Technol., 2006, 200, 4072–4077.

9. K. E. Lee, J. Y. Lee, M. J. Park, J. H. Kim, C. B. Lee and C. O.

Kim: ‘Preparation of boron carbide thin films for HDD

protecting layer’, J. Magn. Magn. Mater., 2004, 272–276, 2197–

2199.

10. P. Dunner, H. J. Heuvel and M. Horle: ‘Absorber materials for

control rod systems of fast breeder reactors’, J. Nucl. Mater.,

1984, 124, 185–194.

11. C. Dominguez, N. Cocuaud, D. Drouan, A. Constant and

D. Jacquemain: ‘Investigation on boron carbide oxidation for

nuclear reactor safety: experiments in highly oxidizing conditions’,

J. Nucl. Mater., 2008, 374, 473–481.

12. N. Seiler, F. Bertrand, O. Marchand, G. Repetto and S. Ederli:

‘Investigations on boron carbide oxidation for nuclear reactors

safety – general modeling for ICARE/CATHARE code applica-

tions’, Nucl. Eng. Design, 2008, 238, 820–836.

13. A. Riyas, K. Divan, M. Alagon and P. Mohanakrishnan: ‘A new

physics design of control safety rods for prototype fast breeder

reactor’, Ann. Nucl. Energ., 2008, 35, 1484–1491.

14. D. Emin and T. L. Aselage: ‘A propeosed boron-carbide-based

solid-state neutron detector’, J. Appl. Phys., 2005, 97, 013529?1–

013529?3

15. O. Gebhardt and D. Gavillet: ‘SIMS imaging analyses of in-

reactor irradiated boron carbide control rod samples’, J. Nucl.

Mater., 2000, 279, 368–371.

16. http://www.iaea.org/inisnkm/nkm/aws/fnss/fulltext/0884_15.pdf

17. V. D. Risovany, A. V. Zakharov, E. P. Klochkov, A. G.

Osipenko, N. S. Kosuling and G. I. Mikhailichenko:

‘Reprocessing of the irradiated boron carbide enriched by

boron-10 isotope and its reuse in the control rods of the fast

breeder reactors’, Proc. Techn. Committ. Meet. on ‘absorber

materials, control rods and designs of backup reactivity shutdown

systems for breakeven cores and burner cores for reducing

plutonium stockpiles’, Obninsk, Russia, July 1995, International

Atomic Energy Agency, IAEA-TECDOC--884, Vols. 3–7, 214–

219.

18. R. Jimbou, M. Saidoh, K. Nakamura, M. Akiba, S. Suzuki,

Y. Gotoh, Y. Suzuki, A. Chiba, T. Yamaki, M. Nakagawa,

K. Morita and B. Tsuchiya: ‘New composite composed of boron

carbide and carbon fiber with high thermal conductivity for first

wall’, J. Nucl. Mater., 1996, 233–237, 781–786.

19. P. Valentine, P. W. Trester, J. Winter, J. Linke, R. Duwe,

E. Wallura and V. Philips: ‘Boron carbide based coatings on

graphite for plasma-facing components’, J. Nucl. Mater., 1994,

212–215, 1146–1152.

20. R. Jimbou, K. Kodama, M. Saidoh, Y. Suzuki, M. Nakagawa,

K. Morita and B. Tsuchiya: ‘Thermal conductivity and retention

characteristics of composites made of boron carbide and carbon



Pub

lishe

d by

Man

ey P

ublis

hing

(c)

IOM

Com

mun

icat

ions

Ltd

fibers with extremely high thermal conductivity for first wall

armour’, J Nucl. Mater., 1997, 241–243, 1175–1179

21. J. G. V. D. Laan, G. Schenedecker, E. V. V. Osch, R. Duwe and

J. Linke: ‘Plasma sprayed boron carbide coating for first wall

protection’, J. Nucl. Mater., 1994, 211, 135–140.

22. D. Gosset and B. Provot: ‘Boron carbide as a potential inert

matrix: an evaluation’, Prog. Nucl. Energy, 2001, 38, (3–4), 263–

266.

23. M. W. Mortensen, P. G. Sorensen, O. Bjorkdahl, M. R. Jensen,

H. J. G. Gundersen and T. Bjornholm: ‘Preparation and

characterization of boron carbide nanoparticles for use as a novel

agent in T cell-guided boron neutron capture therapy’, Appl.

Radiat. Isotopes, 2006, 64, 315–324.

24. S. Sasaki, M. Takeda, K. Yokoyama, T. Miura, T. Suzuki,

H. Suematsu, W. Jiang and K. Yatsui: ‘Thermoelectric properties

of boron carbide thin film and thin film based thermoelectric

device fabricated by intense-pulsed ion beam evaporation’, Sci.

Technol. Adv. Mater., 2005, 6, 181–184.

25. S. Lee and J. Mazurowski: ‘Characterization of boron carbide

thin films fabricated by plasma enhanced chemical vapour

deposition from boranes’, J. Appl. Phys., 1992, 72, (10), 4925–

4932.

26. M. Bouchacoart and F. Thevenot: ‘The correlation between the

thermoelectric properties and stoichiometric properties and

stoichiometry in the boron carbide phase B4C-B10?5C’, J. Mater.

Sci., 1985, 20, 1237–1247.

27. H. Zhao, Y. He and Z. Jin: ‘Preparation of zirconium boride

powder’, J. Am. Ceram. Soc., 1995, 78, (9), 2534–2536.

28. C. Subramanian, T. S. R. Ch. Murthy and A. K. Suri: ‘Synthesis

and consolidation of titanium diboride’, Int. J. Refract. Met. Hard

Mater., 2007, 25, 345–350.

29. T. S. R. Ch. Murthy, B. Basu, R. Balasubramanian, A. K. Suri,

C. Subramanian and R. K. Fotedar: ‘Processing and properties of

TiB2 with MoSi2 sinter additive: a first report’, J. Am. Ceram.

Soc., 2006, 89, (1), 131–138.

30. C. C. Klepper: ‘Sintered boron as high-strength lightweight

structural material for aerospace vehicles’, available at: http://

optics.nasa.gov/tech_days/tech_days_2005/

31. D. Emin: ‘Unusual properties of icosahedral boron-rich solids’,

J. Solid State Chem., 2006, 179, 44–51.

32. M. Bouchacourt and F. Thevenot: ‘The properties and structure

of the boron carbide phase’, J. Less Comm. Met., 1981, 82, 227–

235.

33. M. Bouchacourt and F. Thevenot: ‘Analytical investigations in

the BC system’, J. Less Comm. Met., 1981, 82, 219–226.

34. M. Bouchacourt and F. Thevenot: ‘The melting of boron carbide

and the homogeneity range of the boron carbide phase’, J. Less

Comm. Met., 1979, 67, 327–331.

35. D. Gosset and M. Colin: ‘Boron carbides of various compositions:

an improved method for x-ray characterisation’, J. Nucl. Mater.,

1991,183, 161–173.

36. K. A. Schwetz and P. Karduck: ‘Investigations in the boron

carbon system with the aid of electron probe microanalysis’,

J. Less Comm. Met., 1991, 175, 1–11.

37. M. Beauvy: ‘Stoichiometric limits of carbon-rich boron carbide

phases’, J. Less Comm. Met., 1983, 90, 169–175.

38. R. Lazzari, N. Vast, J. M. Besson, S. Baroni and A. D. Corso:

‘Atomic structure and vibrational properties of icosahedral B4C

boron carbide’, Phys. Rev. Lett., 1999, 83, (16), 3230–3233.

39. Y. Feng, G. T. Seidler, J. O. Cross, A. T. Macrander and J. J.

Rehr: ‘Role of inversion symmetry and multiple effects in non-

resonant X-ray raman-scattering from icosahedral B4C’, Phys.

Rev. B, 2006, 69B, 125402-1–8.

40. D. R. Tallant, T. L. Aselage, A. N. Campbell and D. Emin:

‘Boron carbide structure by Raman spectroscopy’, Phys. Rev. B,

1989, 40B, (8), 5649–5656.

41. F. Mauri, N. Vast and C. J. Pickard: ‘Atomic structure of

icosahedra B4C boron carbide from a first principles analysis of

NMR spectra’, Phys. Rev. Lett., 2001, 87, (8), 085506-1–4.

42. G. H. Kwei and B. Morosin: ‘Structures of boron rich boron

carbides from neutron powder diffraction: implications for the

nature of the Inter-icosahedral chains’, J. Phys. Chem., 1996, 100,

8031–8039.

43. D. D. Radev, B. Mihailova and L. Konstantinov: ‘Raman

spectroscopy study of metal containing boron carbide based

ceramics’, Solid State Sci., 2002, 4, 37–41.

44. H. K. Clark and J. L. Hoard: ‘The crystal structure of boron

carbide’, J. Am. Chem. Soc., 1943, 65, 2115.

45. T. M. Duncan: ‘The distribution of carbon in boron carbide: a 13C

nuclear magnetic resonance study’, J. Am. Chem. Soc., 1984, 106,

2270–2275.

46. J. E. Saal, S. Shang and Z. K. Liu: ‘The structural evolution of

boron carbide via ab initio calculations’, App. Phys. Lett., 2007,

91, 231915-1–3.

47. A. H. Silver and P. J. Bray: ‘Nuclear magnetic resonance study of

boron carbide’, J. Chem. Phys., 1959, 31, (1), 247.

48. M. M. Balkrishnarajan, P. D. Panchratna and R. Hoffman:

‘Structure and bonding in boron carbide: the invincibility of

imperfections’, New J. Chem., 2007, 31, 473–485.

49. C. Wood and D. Emin: ‘Conduction mechanism in boron

carbide’, Phys. Rev. B, 1984, 29B, (8), 4582.

50. R. Schmechel and H. Werheit: ‘Structural defects of some

icosahedral boron-rich solids and their correlation with the

electronic properties’, J. Solid State Chem., 2000, 154, 61–67.

51. U. Kuhlmann and H. Werheit: ‘On the microstructure of boron

carbide’, Solid State Commun., 1992, 83, 849–852.

52. D. Ghosh, G. Subhash, T. S. Sudarshan, R. Radhakrishnan:

‘Dynamic indentation response of fine-grianed boron carbide’,

J. Am. Ceram. Soc., 2007, 90, (6), 1850–1857.

53. X. Q. Yan, Z. Tang, L. Zhang, J. J. Guo, C. Q. Jin, Y. Zhang,

T. Goto, J. W. McCauley and M. W. Chen: ‘Depressurization

amorphization of single-crystal boron carbide’, Phys. Rev. Lett.,

2009, 102, 075505-1–4.

54. D. Lezhava, G. Darsavelidze, D. Gabunia, O. Tsagareishvili,

M. Antadze and V. Gabunia: ‘Influence of carbon content on

physicomechanical characteristics of boron carbide’, J. Solid State

Chem., 2006, 179, 2934–2938.

55. T. Matsui, Y. Arita, K. Naito and H. Imami: ‘High temperature

heat capacities and electrical conductivities of boron carbides’,

J. Nucl. Mater., 1991, 186, 7–12.

56. C. Wood, D. Emin and P. E. Gray: ‘Thermal conductivity of

boron carbides’, Phys. Rev. B, 1985, 31B, (10), 6811.

57. K. E. Gilchrist and S. D. Preston: ‘Thermophysical property

measurements on some neutron absorbing materials’, High Temp.

High Press., 1979, 11, 643–651.

58. G. S. Karumidze and L. A. Shengelia: ‘Isotopic effect of boron

carbide thermal conductivity’, Diamond Relat. Mater., 1993, 3,

14–16.

59. K. Froment, D. Gosset, M. Guery, B. Kryger and C. Verdeau:

‘Neutron irradiation effects in boron carbides: evolution of

microstructure and thermal properties’, J. Nucl. Mater., 1992,

188, 185–188.

60. F. J. Homan: ‘Performance modelling of neutron absorbers’,

Nucl. Technol., 1972, 16, (1), 216–225.

61. Ph. Dunner, H. J. Heuvel, M. Horle: ‘Absorber materials for

control rod systems of fast breeder reactors’, J. Nuc. Mater., 1984,

124, (C), 185–194.

62. T. Maruyama and T. Iseki: ‘Irradiation response and tritium

release behaviour of boron carbide’, J. Nuc. Mater., 1985, 133–

134, 727–731.

63. G. W. Hollenberg, W. V. Cummings: ‘Effect of fast neutron

irradiation of the structure of boron carbide’, J. Am. Ceram. Soc.,

1977, 60, (11–12), 520–525.

64. T. Kaito, T. Maruyama, S. Onose and H. Horiuchi: ‘Irradiation

behavior of boron carbide neutron absorber’, available at:

www.iaea.or.atinisawsfnssfulltext0884_17.pdf

65. G. I. Copeland, C. K. H. Dubose, R. G. Donnelly and W. R.

Martin: ‘Transmission electron microscopy of irradiated boron

carbide’, J. Nucl. Mater., 1972, 43, 126–132.

66. G. L. Copeland, R. G. Donnelly and W. R. Martin: ‘Irradiation

behavior of boron carbide’, Nulc. Technol., 1972, 16, (1), 226–237.

67. H. Inui, H. Mori and H. Fujita: ‘Electron irradiation induced

crystalline to amorphous transition in boron carbide’, Scr.

Metall., 1988, 22, 249–254.

68. Y. Morohashi, T. Maruyama, T. Donomae, Y. Tachi and

S. Onose: ‘Neutron irradiation effect on isotopically tailored11B4C’, J Nucl. Sci. Technol., 2008 45, (9), 867–872

69. R. R. Ridgway: ‘Boron carbide and the method of making the

same’, US patent no. 1897214, 1933.

70. M. T. Spohn: ‘Boron carbide’, Am. Ceram. Soc. Bull., 1993, 72,

(6), 88.

71. G. Goller, C. Toy, A. Tekin and C. K. Gupta: ‘The production of

boron carbide by carbothermic reduction’, High Temp. Mater.

Proc., 1996, 15, (1–2), 117–122.

72. F. Schroll and A. Vogt: ‘Electrothermic production of boron

carbide’, US patent no. 2 163 293, 1939.

73. J. J. Scott: ‘Arc furnace process for the production of boron

carbide’, US patent no. 3 161 471, 1964.



Pub

lishe

d by

Man

ey P

ublis

hing

(c)

IOM

Com

mun

icat

ions

Ltd

74. R. R. Ridgeway: ‘Methods of making abrasive metal carbides’,

US patent no. 2 155 682, 1939.

75. M. P. L. N. Rao, G. S. Gupta, P. Manjunath, S. Kumar, A. K.

Suri, N. Krishnamurthy and C. Subramanian: ‘Temperature

measurements in the boron carbide manufacturing process – a hot

model study’, Int. J. Refract. Met. Hard Mater., 2009, 27, (3),

621–628.

76. M. P. L. N. Rao, G. S. Gupta, P. Manjunath, S. Kumar, A. K.

Suri, N. Krishnamurthy and C. Subramanian: ‘Core temperature

measurement in carbothermal reduction process’, Thermochim.

Acta, 2009, 482, 66–71.

77. D. K. Bose, K. U. Nair and C. K. Gupta: ‘Production of high

purity boron carbide’, High Temp. Mater. Proc., 1986, 7, (2–3),

133–140.

78. A. Alizadeh, E. T. Nassaj, N. Ehsani and H. R. Baharvandi:

‘Production of boron carbide powder by carbothermic reduction

from boron oxide and petroleum coke or carbon active’, Adv.

Appl. Ceram., 2006, 105, (6), 291–296.

79. A. Alizadeh, E. T. Nassaj and N. Ehsani: ‘Synthesis of boron

carbide powder by a carbothermic reduction method’, J. Eur.

Ceram. Soc., 2004, 24, 3227–3234.

80. C. Subramanian and A. K. Suri: ‘Development of boron based

neutron absorber materials’, Met. Mater. Process., 2004, 16, (1),

39–52.

81. A. W. Weimer W. G. Moore R. P. Roach, J. E. Hitt, R. S. Dixit

and S. E. Pratsinis: ‘Kinetics of carbothermal reduction synthesis

of boron carbide’, J. Am. Ceram. Soc., 1992, 75, (9), 2509–2514.

82. B. Z. Dacic, V. Jokanovic, B. Jokanovic and M. D. Dramicanin:

‘Thermodynamics of gas phase carbothermic reduction of boron-

anhydride’, J. Alloys Compd, 2006, 413, 198–205.

83. Yu. N. Tumanov: ‘The synthesis of boron carbide in a high

frequency electromagnetic field’, J. Less Comm. Met., 1979, 67,

521–529.

84. W. Rafaniello and W. G. Moore: ‘Producing boron carbide’, US

patent no. 4 804 525, 1989.

85. A. W. Weimer, W. G. Moore and R. P. Roach: ‘Method for

producing uniform, fine boron containing ceramic powders’, US

patent no. 5 194 234, 1993.

86. A. W. Weimer, W. G. Moore and R. P. Roach: ‘Apparatus for

producing uniform fine ceramic powders’, US patent no. 5 110

565, 1992.

87. S. Herth, W. J. Joost, R. H. Doremus and R. W. Siegel: ‘New

approach to the synthesis of nanocrystalline boron carbide’,

J. Nanosci. Nanotechn., 2006, 6, (4), 954–959.

88. B. Chang, B. L. Gersten, S. T. Szewczyk and J. W. Adams:

‘Towards the preparation of boron carbide nanorods by

carbothermal reaction method’, NSTI Nanotech 2006 Techn.

Proc., 2006, 1, 369–372.

89. R. Ma and Y. Bando: ‘High purity single crystalline boron

carbide nanowires’, Chem. Phys. Lett., 2002, 364, 314–317.

90. L. H. Bao, C. Li, Y. Tian, J. F. Tian, C. Hui, X. J. Wang, C. M.

Shen and H. J. Gao: ‘Synthesis and photoluminescence property

of boron carbide nanowires’, Chin. Phys. B, 2008, 17B, (12), 4585–

4591.

91. F. F. Xu and Y. Bando: ‘Formation of two-dimensional

nanomaterials of boron carbides’, J. Phys. Chem. B, 2004, 108B,

7651–7655.

92. C. H. Jung, M. J. Lee and C. J. Kim: ‘Preparation of carbon free

B4C powder from B2O3 oxide by carbothermal reduction process’,

Mater. Lett., 2004, 58, 609–614.

93. A. Aghai, C. Falamaki, B. E. Yekta and M. S. Afarani: ‘Effect of

seeding on the synthesis of B4C by the magnesiothermic reduction

route’, Ind. Ceram., 2002, 22, (2), 121–125.

94. E. G. Gray: ‘Process for the production of boron carbide’, US

patent no. 2 834 651, 1958

95. A. Muta and T. Geja: ‘Method for producing boron carbide’, US

patent no. 3 338 679, 1967

96. T. A. Zhang Z. H. Dou, H. Yang and Q. L. Ding: ‘Preparation of

boron carbide by magnesium reducing – SHS’, J. North Eastern

Univ., 2003, 24, (10) 935–938.

97. A. K. Khanra and M. M. Godkhindi: ‘Synthesis of boron carbide

by self –propagating high temperature synthesis’, J. Aust. Ceram.

Soc., 2005, 41, (1), 30–35.

98. F. Deng, H. Y. Xie and L. Wang: ‘Synthesis of submicron B4C by

mechanochemical method’, Mater. Lett., 2006, 60, (13–14), 1771–

1773.

99. L. L Wang, Z. A. Munir and J. B. Holt: ‘The feasibility of

synthesis of B4C fiber –MgO composites by combustion’, Scr.

Metall. Mater., 1994, 31, (1), 93–97.

100. L. J. Berchmans, V. Mani and K. Amalajyothi: ‘Synthesis of

boron carbide by calciothermic reduction process’, Int. J. Self-

propagat. High Temp. Synth., 2009, 18, (1), 60–63.

101. I. A. Bairamashvili: ‘Experience in production of articles from

boron carbide for fast reactor control rods’, Proc. Techn.

Committ. Meet. on ‘absorber materials, control rods and designs

of backup reactivity shutdown systems for breakeven cores and

burner cores for reducing plutonium stockpiles’, Obninsk, Russia,

July 1995, International Atomic Energy Agency, IAEA-TEC

DOC--884, 220–224.

102. X. Guangshan, Z. Ruxian, W. Yonglan and L. Shikun: ‘Control

assembly to be used in CEFR’, Proc. Techn. Committ. Meet. on

‘absorber materials, control rods and designs of backup reactivity

shutdown systems for breakeven cores and burner cores for

reducing plutonium stockpiles’, Obninsk, Russia, July 1995,

International Atomic Energy Agency, IAEA-TECDOC--884,

47–52.

103. A. W. Weimer: ‘Carbide, nitride and boride materials, synthesis

and processing’, 89–95; 1997, London, Chapman & Hall.

104. K. U. Nair, D. K. Bose and C. K. Gupta: ‘The production of

elemental boron by fused salt electrolysis’, Miner. Proc. Extract.

Metall. Rev., 1992, 9, 283–291.

105. A. Jain, S. Anthonysamy, K. Ananthasivan, R. Ranganathan,

V. Mittal, S. V. Narsimhan and V. Mittal: ‘Charecterization of

electrodeposited elemental boron’, Mater. Charact., 2008, 59,

890–900.

106. E. M. Heian, S. K. Khalsa, T. Yamamoto and M. Ohyanagi:

‘Synthesis of dense, high-defect-concentration B4C through

mechanical activation and field assisted combustion’, J. Am.

Ceram. Soc., 2004, 87, (5), 779–783.

107. K. Yamada: ‘Boron carbide articles formed from an amorphous

boron/graphite powder mixture using a shock wave technique’,

J. Am. Ceram. Soc., 1996, 79, (4), 1113–1116.

108. J. Wei, B. Jiang, Y. Li, C. Xu and D. Wu: ‘Straight boron carbide

nanorods prepared from carbon nanotubes’, J. Mater. Chem.,

2002, 12, 3121–3124.

109. S. Chen, D. Z. Wang, J. Y. Huang and Z. F. Ren: ‘Synthesis and

characterization of boron carbide nanoparticles’, Appl. Phys. A,

2004, 79A, (7), 1757–1759.

110. B. Chang, B. L. Gersten, S. T. Szewczyk and J. W. Adams:

‘Characterization of boron carbide nanoparticles prepared by a

solid state thermal reaction’, Appl. Phys. A, 2007, 86A, 83–

87.

111. S. T. Benton and R. David: ‘Methods for preparing boron carbide

articles’, US patent no. 3 914 371, 1975.

112. A. S. Ramos, S. P. Taguchi, E. C. T. Ramos, V. L. Arantes and

S. Ribeiro: ‘High energy ball milling of powder B-C mixture’,

Mater. Sci. Eng. A, 2006, 422A, (1–2), 184–188.

113. U. A. Tamburini, Z. A. Munir, Y. Kodera, T. Imai and

M. Ohyanagi: ‘Influence of synthesis temperature on the defect

structure of boron carbide: experimental and modeling studies’,

J. Am. Ceram. Soc., 2005, 88, (6), 1382–1387.

114. R. G. Bourdio: ‘Process of preparing boron carbide from boron

halide and a hydrocarbon’, US patent no. 3 334 967, 1967.

115. R. A. Clifton: ‘Production of boron carbide whiskers’, US patent

no. 3 525 589, 1970.

116. E. W. James: ‘Catalyst for growth of boron carbide crystal

whiskers’, US patent no. 3 423 179, 1969.

117. J. F. Ditter, F. J. Gerhart and R. E. Williams: ‘Boron carbide’, US

patent no. 4 017 587, 1977.

118. I. M. MacKinnon and B. G. Reuben: ‘The synthesis of boron

carbide in an RF plasma’, J. Electrochem. Soc., 1975, 122, (6),

806–811.

119. B. Zeng, Z. Feng, S. Li, Y. Liu, L. Cheng and L. Zhang:

‘Microstructure and deposition mechanism of CVD amorphous

boron carbide coatings deposited on SiC substrates at low

temperature’, Ceram. Int., 2009, 35, 1877–1882.

120. E. Wainer, S. Heights and M. S. Vukasovich: ‘Preparation of

carbide structures’, US patent no. 3 269 802, 1966.

121. J. Economy, R. Y. Lin and W. D. Smith: ‘High strength yarn

consisting of boron carbide fibers’, US patent no. 4 238 547, 1980.

122. M. Jazirehpour and A. Alizadeh: ‘Synthesis of boron carbide

core- shell nanorods and a qualitative model to explain the

formation of rough shell nanorods’, J. Phy. Chem., 2009, 113,

1657–1661.

123. M. Shu Fang, L. Jian, Z. Jun-Fu, S. Xiao-Xia and X. Bing-She:

‘Effect on graphite substrate to formation of boron carbide/

carbon composite nanoropes’ Chn J. Inorg. Chem. 2009, 25, (6),

1050–1054.



Pub

lishe

d by

Man

ey P

ublis

hing

(c)

IOM

Com

mun

icat

ions

Ltd

124. M. Karaman, N. A. Sezgi, T. Dogu and H. O. Ozbelge: ‘Kinetic

investigation of chemical vapour depositionof B4C on Tungsten

substrate’, AIChE J., 2006, 52, (12), 4161–4166.

125. M. C. Schouler, M. C. Cheynet, K. Sestier, J. Garden and

P. Gadelle: ‘New filamentous deposites in the boron-carbon

system’, Carbon, 1997, 35, (7), 993–1000.

126. A. O. Sezer and J. I. Brand: ‘Chemical vapor deposition of boron

carbide’, Mater. Sci. Eng. B, 2001, B79, 191–202.

127. M. J. Santos, A. J. Silvestre and O. Conde: ‘Laser-assisted

deposition of r-B4C coatings using ethylene as carbon precursor’,

Surf. Coat. Technol., 2002, 151–152, 160–164.

128. J. C. Oliveira, P. Paiva, M. N. Oliveira and O. Conde: ‘Laser-

assisted CVD of boron carbide at atmospheric pressure’, Appl.

Surf. Sci., 1999, 138–139, 159–164.

129. J. C. Oliveira and O. Conde: ‘Deposition of boron carbide by laser

CVD: a comparison with thermodynamic predictions’, Thin Solid

Films, 1997, 307, 29–37.

130. H. Vincent, C. Vincent, M. P. Berthet, J. Bouix and G. Gonzalez:

‘Boron carbide formation from BCl3–CH4–H2 mixtures on carbon

substrates and in a carbon fibre reinforced Al composite’, Carbon,

1996, 34, (9), 1041–1055.

131. M. Olsson, S. Soderberg, B. Stridh and J. O. Carlsson: ‘Chemical

vapour deposition of boron carbide: morphology and micro-

structure’, Thin Solid Films, 1989, 172, (1), 95–109.

132. U. Jansson, J. O. Carlsson, B. Stridh, S. Soderberg and M. Olsson:

‘Chemical vapor deposition of boron carbides: phase and

chemical composition’, Thin Solid Films, 1989,172, (1),81–93.

133. S. Mierzejewska and T. Niemyski: ‘Preparation of crystalline

boron carbide by vapour phase reaction’, J. Less Comm. Met.,

1965, 8, 368–374.

134. R. E. Riley, L. R. Newkirk F. A. Valencia,S, Wallace and

C. Terry: ‘Preparation and uses of amorphous boron carbide

coated substrates’, US patent no. 4 287 259, 1981.

135. R. L. Heetstand and C. F. Leitten: ‘Boron carbide article and

method of making’, US patent no. 3 367 826, 1968.

136. J. G. Donaldson, J. B. Stephenson and A. A. Coachran: ‘Boron

and boron carbide by vapor deposition’, Electrodepos. Surf.

Treat., 1973/1974, 2, 149–163.

137. J. Berjonneau, G. Chollon and F. Langlais: ‘Deposition process

for amorphous boron carbide from CH4/BCl3/H2 precursor’,

J. Electrochem. Soc., 2006, 153, (12), C795–C800.

138. J. C. Oliveira, M. N. Oliveira and O. Conde: ‘Structural

characterization of B4C films deposited by laser assisted CVD’,

Surf. Coat. Technol., 1996, 80, 100–104.

139. A. K. Knudsen and C. A. Langhoff: ‘Process for the preparation

of submicron sized boron carbide powders’, US patent no. 4 895

628, 1990.

140. T. Oyama and K. Takeeuchi: ‘Gas-phase synthesis of crystalline

B4C encapsulated in graphite particles by pulsed-laser irradiation’,

Carbon 1999, 37, 433–436.

141. D. Zhang, D. N. Mcilroy, Y. Geng and M. G. Norton: ‘Growth

and charactrization of boron carbide nanowires’, J Mater. Sci.

Lett., 1999, 18, 349–351.

142. V. Cholet, R. Herbin and L. Vandenbulcke: ‘Chemical vapour

deposition of boron carbide from BBr3–CH4–H2 mixtures in a

microwave plasma’, Thin Solid Films, 1990, 188, 143–155.

143. O. Postel and J. Heberlein: ‘Deposition of boron carbide thin film

by supersonic plasma jet CVD with secondary discharge’, Surf.

Coat. Technol., 1998, 108–109, 247–252.

144. K. Kunihito, S. Tsutomu, P. C. Hoon and Y. Hiroaki: ‘CVD

synthesis and thermoelectric properties of boron carbide’,

J. Ceram. Soc. Jpn, 1992, 100, (1162), 853–857.

145. T. S. Moss, L. W. Jack and K. L. More: ‘Chemical vapour

deposition of B13C2 from BCl3–CH4–H2–argon mixtures’, J. Am.

Ceram. Soc., 1998, 81, (12), 3077–3086.

146. S. V. Deshpande, E. Gulari, S. J. Harris, A. M. Weiner and

M. Anita: ‘Filament activated chemical vapor deposition of boron

carbide coating’, Appl. Phys. Lett., 1994, 65, (14), 1757–1759.

147. I. Caretti, R. Gago, J. M. Albella and I. Jimenez: ‘Boron carbides

formed by coevaporation of B and C atoms: ‘Vapor reactivity,

BxC12x composition, and bonding structure’, Phys. Rev. B, 2008,

77B, 174109-1.

148. W. J. Lackey, D. Rosen, C. E. Duty, D. L. Jean, S. N. Bondi and

T. N. Elkhatib: ‘Laser CVD system design operation, and

modeling’, Ceram. Eng. Sci. Proc., 2002, 23, (4), 23–33.

149. H. O. Pierson: ‘Handbook of chemical vapor deposition:

principles, technology and application’; 1992, Park Ridge, NJ,

Noyes Publications.

150. K. Osberg, N. Schemm, S. Balkir, J. I. Brand, S. Hallbeck and

P. Dowbent: ‘A hand-held neutron detection sensor system’, Proc.

Int. Symp. on ‘Circuits and systems’, Island of Kos, Greece, May

2006, IEEE, 1179–1182.

151. S. Lee and P. A. Dowben: ‘The properties of boron carbide/silicon

hetrojunction diodes fabricated by plasma-enhanced chemical

vapor deposition’, Appl. Phys. A, 1994, 58A, 223–227.

152. D. Byun, S. D. Hwang, P. A. Dowben, F. K. Perkins, F. Filips

and N. J. Ianno: ‘Heterojunction fabrication by selective area

chemical vapor deposition induced by synchrotron radiation’,

Appl. Phys. Lett., 1994, 64, (15), 1968–1970.

153. S. D. Hwang, D. Byun, N. J. Ianno, P. A. Dowben and H. R.

Kim: ‘Fabrication of boron–carbide/boron hetrojunction devices’,

Appl. Phys. Lett., 1996, 68, (11), 1495–1497.

154. B. W. Robertson, S. Adenwalla, A. Harken, P. Welsch, J. I.

Brand, P. A. Dowben, and J. P. Classen: ‘A class of boron –rich

solid state neutron detectors’, Appl. Phys. Lett., 2002, 80, (19),

3644–3646.

155. S. Adenwalla, P. Welsch, A. Harken, J. I. Brand, A. Sezer and

B. W. Robertson: ‘Boron carbide/n-silicon carbide heterojunction

diodes’, Appl. Phys. Lett., 2001, 79, (26), 4357–4359.

156. G. L. Harris and D. S. Parsons: ‘Method of producing boron

carbide from water alcohol solution of carbon source’, US patent

no. 3 885 022, 1975.

157. S. Mondal and A. K. Banthia: ‘Low temperature synthetic route

for boron carbide’, J. Eur. Ceram. Soc., 2005, 25, 287–291.

158. A. Sinha, T. Mahata and B. P. Sharma: ‘Carbothermal route for

preparation of boron carbide powder from boric acid-citric acid

gel precursor’, J. Nucl. Mater., 2002, 301, 165–169.

159. J. Economy and I. Matkowich: ‘Boron carbide fiber production’,

US patent no. 3 825 469, 1974.

160. S. Cihangir, C. Ergun, S. Yilmaz and F. C. Sahin: ‘Synthesis of

B4C/SiC composite from sugar based precursor’, Diffus. Defect

Data A, 2008, 283–286A, 268–272.

161. I. Yanase, R. Ogawara and H. Kobayashi: ‘Synthesis of boron

carbide powder from polyvinyl borate precursor’, Mater. Lett.,

2009, 63, 91–93.

162. A. M. Hadian and J. A. Bigdeloo: ‘The effect of time, temperature

and composition on boron carbide synthesis by sol-gel method’,

J. Mater. Eng. Perform., 2008, 17, (1), 44–49.

163. H. Konno, A. Sudoh, Y. Aoki and H. Habazaki: ‘Synthesis of

C/B4C composites from sugar–boric acid mixed solutions’, Mol.

Cryst. Liq. Crys. A, 2002, 386A, (1), 15–20.

164. I. Hasegawa, Y. Fujii, T. Takayama and K. Yamada: ‘Phenolic

resin–boron oxide hybrids as precursors for boron carbide’,

J. Mater. Sci. Lett., 1999, 18, 1629–1631.

165. M. G. L. Mirabelli and L. G. Sneddon: ‘Synthesis of boron

carbide via Poly vinylpentaborane precursors’, Am. Chem. Soc.,

1988, 110, (10), 3305–3307.

166. H. Wada, S. Ito, K. Kuroda and C. Kato: ‘The synthesis of boron

nitride and boron carbide by pyrolysis of boric acid/1,2,3-

prpanetriol condensation product’, Chem. Lett., 1985, 14, (6),

691–692.

167. J. G. Joseph: ‘Process for depositing boron carbide’, US patent

no. 3 480 467, 1969.

168. L. Shi, Y. Gu, L. Chen, Y. Qian, Z. Yang and J. Ma: ‘A low

temperature synthesis of crystalline B4C ultrafine powders’, Solid

State Commun., 2003, 128, 5–7.

169. Y. Gu, L. Chen, Y. Qian, W. Zhang and J. Ma: ‘Synthesis of

nanocrystalline boron carbide via a solvothermal reduction of

CCl4 in the presence of amorphous boron powder’, J. Am. Ceram.

Soc., 2005, 88, (1), 225–227.

170. C. Ronning, D. Schwen, S. Eyhusen, U. Vetter and H. Hofsass:

‘Ion beam synthesis of boron carbide thin films’, Surf. Coat.

Technol., 2002, 158–159, 382–387.

171. B. M. Todorovic, I. Draganic, D. Vasiljevic-Radovic,

N. Romdevic, M. Romccevic, M. Dramicanin and Z. Markovic:

‘Synthesis of amorphous boron carbide by single and multiple

charged boron ions bombardment of fullerene thin films’, Appl.

Surf. Sci., 2007, 253, 4029–4053.

172. M. Carlsson, F. J. G. Garcia, M. Johnsson: ‘Synthesis and

characterization of boron carbide whiskers and thin elongated

platelets’, J. Cryst. Growth, 2002, 236, 466–476.

173. R. V. Krishnarao and J. Subrahmanyam: ‘Studies on the

formation of whiskers and platelets of B4C and BN’, J. Mater.

Sci., 2004, 39, 6263–6269.

174. X. An, H. Zhai, H. Zhai, C. Cao and H. Zhu: ‘Synthesis and

characterization of boron carbide nanobelts’, Key Eng. Mater.,

2007, 336–338, (III), 2166–2168.

175. R. Ma and Y. Bando: ‘Investigation on the growth of boron

carbide nanowires’, Chem. Mater., 2002, 14, 4403–4407.



Pub

lishe

d by

Man

ey P

ublis

hing

(c)

IOM

Com

mun

icat

ions

Ltd

176. N. R. Thakkar and R. G. Reddy: ‘Thermal plasma processing of

boron carbide fine powders’, Mater. Sci. Technol. 2003 Meet.,

2003, 23, 47–60

177. J. L. He: ‘Carbon rich boron carbide in the eutectic product

synthesized by resistance heating of B2CN in graphite’, J. Alloys

Compd, 2007, 437, 238–246.

178. F. F. Lange: ‘Densification of powder compacts: an unfinished

story’, J. Eur. Ceram. Soc., 2008, 28, (7), 1509–1516.

179. L. S. Dole, S Prochazka and R H. Doremus: ‘Microstructural

coarsening during sintering of boron carbide’, J. Am. Ceram. Soc.,

1989, 72, (6), 958–966.

180. M. A. Kuzenkova, P. S. Kisly, B. L. Grabchuk and N. I.

Bodnaruk: ‘Structure and properties of sintered boron carbide’,

Powder Metall. Int., 1980, 12, (1), 11–13.

181. M. A. Kuzenkova, P. S. Kislyi, B. L. Grabchuk and N. I.

Bodnaruk: ‘The structure and properties of sintered boron

carbide’, J. Less Comm. Met., 1979, 67, 217–223.

182. B. L. Grabchuk and P. S. Kislyi: ‘Some features of the sintering

behavior of pure and technical boron carbide’, Sov. Powder

Metall., 1976, 15, (9), 675–678.

183. H. Lee and R. F. Speyer: ‘Pressureless sintering of boron carbide’,

J. Am. Ceram. Soc., 2003, 86, (9), 1468–1473.

184. R. F. Speyer and J. Lee: ‘Advances in pressureless densification of

boron carbide’, J. Mater. Sci., 2004, 39, 6017–6021.

185. X. Zhu, K. Lu and K. Nagarathnam: ‘Compaction of different

boron carbide powders using uniaxial die compaction and

combustion driven compaction’, J. Mater. Sci., 2009, 44, 414–421.

186. F. Thevenot: ‘Sintering of boron carbide and boron carbide-

silicon carbide two-phase materials and their properties’, J. Nucl.

Mater., 1988, 152, 154–162.

187. L. Levin, N. Frage and M. P. Dariel: ‘A novel approach for the

preparation of B4C-based cermets’, Int. J. Refract. Met. Hard

Mater., 2000, 18, 131–135.

188. N. Frage, L. Levin and M. P. Dariel: ‘The effect of the sintering

atmosphere on the densification of B4C ceramics’, J. Solid State

Chem., 2004, 177, 410–414.

189. K. A. Schwetz and W. Grellner: ‘The influence of carbon on the

microstructure and mechanical properties of sintered boron

carbide’, J. Less Comm. Met., 1981, 82, 37–47.

190. M. Bougoin and F. Thevenot: ‘Pressureless sintering of boron

carbide with an addition of polycarbosilane’, J. Mater. Sci., 1987,

22, (1), 104–109.

191. B. Y. Yin and L. S. wang: ‘Studies on activated sintering of jet

milled B4C powders’, Atom. Energy Sci. Technol., 2003, 37,

(Suppl.), 70–72, 76.

192. J. E. Zorzi, C. A. Perottoni and J. A. H. da Jornada: ‘Hardness

and wear resistance of B4C ceramics prepared with several

additives’, Mater. Lett., 2005, 59, 2932–2935.

193. T. K. Roy, C. Subramanian and A. K. Suri: ‘Pressureless sintering

of boron carbide’, Ceram. Int., 2006, 32, 227–233.

194. A. K. Suri and C. K. Gupta: ‘Studies on the fabrication of

aluminum bonded boron carbide rings’, J. Nucl. Mater., 1978, 74,

297–302.

195. H. R. Baharvandi, A. M. Hadian, H. Abdizade and N. Ehsani:

‘Investigation on addition of talc on sintering behavior and

mechanical properties of B4C’, J. Mater. Eng. Perform., 2006, 15,

(3), 280–283.

196. H. R. Baharvandi, A. M. Hadian, A. Abdizadeh and N. Ehsani:

‘Investigation on addition of ZrO2-3 mol% Y2O3 powder on

sintering behavior and mechanical properties of B4C’, J. Mater.

Sci., 2006, 41, 5269–5272.

197. L. Levin, N. Frage and M. P. Dariel: ‘The effect of Ti and TiO2

additions on the pressureless sintering of B4C’, Metall. Mater.

Trans. A, 1999, 30A, 3201–3210.

198. A. Goldstein, Y. Yeshurun and A. Goldenberg: ‘B4C/metal boride

composites derived from B4C/metal oxide mixtures’, J. Eur.

Ceram. Soc., 2007, 27, (2–3), 695–700.

199. C. H. Lee and C. H. Kim: ‘Pressureless sintering and related

reaction phenomena of Al2O3-doped B4C’, J. Mater. Sci., 1992,

27, (23), 6335–6340.

200. L. S. Sigl: ‘Processing and mechanical properties of boron carbide

sintered with TiC’, J. Eur. Ceram. Soc., 1998, 18, 1521–1529.

201. S. Prochazka and B. Lake: ‘Dense sintered boron carbide

containing beryllium carbide’, US patent no. 4005235, 1977.

202. G. Q. Weaver: ‘Sintered high density boron carbide’, US patent

no. 4 320 204, 1982.

203. S. Yamada, K. Hirao, Y. Yamauchi and S. Kanzaki:

‘Densification behaviour and mechanical properties of pressure-

less-sintered B4C-CrB2 ceramics’, J. Mater. Sci., 2002, 37, 5007–

5012.

204. S. Yamada, K. Hirao, Y. Yamachi and S. Knzaki: ‘Sintering

behaviour of B4C-CrB2 ceramics’, J. Mater. Sci. Lett., 2002, 21,

1445–1447.

205. R. F. Speyer and H. Lee: ‘Improved pressureless densification of

B4C’, Ceram. Trans., 2003, 151, 71–82.

206. B. Y. Yin, L. S. Wang and Y. C. Fang: ‘Sintering mechanism of

pure and carbon-doped boron carbide’, J. Chin. Ceram. Soc.,

2001, 29, (1), 68–71.

207. K. A. Schwetz, G. Vogt and K. S. Mang: ‘Process for the

production of dense sintered shaped articles of polycrystalline

boron carbide by pressureless sintering’, US patent no. 4 195 066,

1980.

208. N. Cho, K. G. Silver, Y. Berta, R. F. Speyer, N. Vanier and C. H.

Hung: ‘Densification of carbon-rich boron carbide nanopowder

compacts’, J. Mater. Res., 2007, 22, (5), 1354–1359.

209. A. Matsumoto, T. Goto and A. Kawakami: ‘Slip casting and

pressureless sintering of boron carbide and its application to the

nuclear field’, J. Ceram. Soc. Jpn, 2004, 112, (5), S399–S402.

210. R. N. J. Taylor: ‘Novel powder processing of sintered boron

carbide’, Key Eng. Mater., 2004, 45–48, 264–268.

211. R, Telle and G. Petzow: ‘Strengthening and toughning of boride

and carbide hard material composites’, Mater. Sci. Eng. A, 1988,

A105/106, 97–104.

212. K. T. Faber and A. G. Evans: ‘Crack deflection processes –

I. Theory’, Acta Metall. 1983, 31, (4), 565–576.

213. H. R. Baharvandi and A. M. Hadian: ‘Pressureless sintering of

TiB2–B4C ceramic matrix composite’, J. Mater. Eng. Perform.,

2008, 17, (6), 838–841.

214. VI. V. Skorokhod and V. D. Krstic: ‘Processing, microstructure

and mechanical properties of B4C–TiB2 particulate sintered

composites. I. Pressureless sintering and microstructure evolu-

tion’, Powder Metall. Met. Ceram., 2000, 39, (7–8), 414–423.

215. V. V. Skorokhod, M. D. Vlajic and V. D. Krstic: ‘Pressureless

sintering of B4C–TiB2 ceramic composites’, Mater. Sci. Forum,

1998, 282–283, 219–224.

216. V Skorokhod, M. D. Vlajic and V. D. Krstic: ‘Mechanical

properties of pressureless sintered boron carbide containing TiB2

phase’, J. Mater. Sci. Lett., 1996, 15, 1337–1339.

217. V. Skorokhod and V. D. Krstic: ‘Processing, microstructure and

mechanical properties of B4C–TiB2 particulate sintered compo-

sites. II. Fracture and mechanical properties’, Powder Metall.

Met. Ceram., 2000, 39, (9–10), 504–513.

218. M. D. Vlajic and V. D. Kristic: ‘Process for the production of

dense boron carbide and transition metal borides’, US patent

no. 5 720 910, 1998.

219. L. Sigl, H. Thaler and K. A. Schwetz: ‘Process for producing

bodies based on boron carbide by pressureless sintering’, US

patent no. 5 505 899, 1996.

220. B. Khazai and W. G. Moore: ‘composition and method for

producing boron carbide/titanium diboride composite ceramic

powders using a boron carbide substrate’, US patent no. 5 108

962, 1992.

221. C. Subramanian, T. K. Roy, T. S. R. Ch. Murthy, P. Sengupta,

G. B. Kale, M. V. Krishnaiah and A. K. Suri: ‘Effect of Zirconia

addition on pressureless sintering of boron carbide’, Ceram. Int.,

2008, 34, 1543–1549.

222. Q. Lin, P. Shen, F. Qiu, D. Zhang and Q. Jiang: ‘Wetting of

polycrystalline B4C by molten Al at 1173–1473 K’, Scr. Mater.,

2009, 60, 960–963.

223. C. H. Danny, J. P. Aleksander, A. A. Ilhan and E. S. William:

‘Processing of boron carbide-aluminum composites’, J. Am.

Ceram. Soc., 1989, 72, (5), 775–780.

224. P. Kewu, W. Wenyuan, X. Jingyu, T. Ganfeng and N. Fuhu:

‘Study on mechanical properties and fracture mechanisms of B4C–

CeB6/Al composites’, J. Rare Earth., 2007, 25, (suppl.), 77–81.

225. K. M. Taylor, N. Falls and R. J. Palicka: ‘Dense carbide

composite for armor and abrasives’, US patent no. 3 765 300,

1973.

226. S. Hayun, A. Weizmann, M. P. Dariel and N. Frage: ‘The effect

of particle size distribution on the microstructure and the

mechanical properties of boron carbide based reaction bonded

composites’, Int. J. Appl. Ceram. Technol., 2009, 6, (4), 492–500.

227. D. Mallick, T. K. Kayal, J. Ghosh, O. P. Chakrabarti, S. Biswas

and H. S. Maiti: ‘Development of multi-phase B–Si–C ceramic

composite by reaction sintering’, Ceram. Int., 2009, 35, (4), 1667–

1669.

228. Z. F. Chen, Y. C. Su and Y. B. Cheng: ‘Formation and sintering

mechanisms of reaction bonded silicon carbide–boron carbide

composites’, Key Eng. Mater., 2007, 352, 207–212.



Pub

lishe

d by

Man

ey P

ublis

hing

(c)

IOM

Com

mun

icat

ions

Ltd

229. J. Y. Liu, C. P. Zou, W. S. Zha, G. H. Liu, J. Lan and Q. H. Feng:

‘Effect of sintering temperature on microstructure and compres-

sive strength of B4C–AlSi eutectic alloy’, Nucl. Power Eng., 2008,

29, (2), 58–60, 104.

230. M. Aizenshtein, I. Mizrahi, N. Froumin, S. Hayun, M. P. Dariel

and N. Frage: ‘Interface interaction in the B4C/(Fe–B–C) system’,

Mater. Sci. Eng. A, 2008, A495, 70–74.

231. I. Mizrahi, A. Raviv, H. Dilman, M. Aizenshtein, M. P. Dariel

and N. Frage: ‘The effect of Fe addition on processing and

mechanical properties of reaction infiltrated boron carbide-based

composites’, J. Mater. Sci., 2007, 42, 6923–6928.

232. M. K. Aghajanian, A. L. McCormick, B. N. Morgan and A. F.

Liszkiewicz: ‘Boron carbide composite bodies, and methods for

making same’, US patent no. 0 169 128 A1, 2006.

233. S. Hayun, D. Rittel, N. Frage and M. P. Dariel: ‘Static and

dynamic mechanical properties of infiltrated B4C–Si composites’,

Mater. Sci. Eng. A, 2008, 487, 405–409.

234. G. T. Burns, G. A. Zankm and J. A. Ewald: ‘Preparation of high

density boron carbide ceramics with preceramic polymer binders’,

US patent no. 5 545 687, 1996.

235. K Hirao, S. Sakaguchi, Y Yamauchi, S Kanzaki and S Yamada:

‘Boron carbide based sintered compact and method for prepara-

tion thereof’, US patent no. 0063583, 2008.

236. P. F. Jahn: ‘Use of alumina alone or with silica as sintering aid for

boron carbide’, US patent no. 3 632 710, 1972.

237. B. Y. Yin and L. S. Wang: ‘Study on physical properties of hot-

pressing sintered B4C ceramic’, Atom. Energy Sci. Technol., 2004,

38, (5), 429–431.

238. M. S. Koval’chenko, Yu. G. Tkachenko, L. F. Ochkas, D. Z.

Yurchenko and V. B. Vinokurov: ‘Densification kinetics of boron

carbide in hot pressing’, Sov. Powder Metall. Met. Ceram., 1987,

26, (11), 881–884.

239. I. T. Ostapenko, V. V. Slezov, R. V. Tarasov, N. F. Kartsev and

V. P. Podtykan: ‘Densification of boron carbide powder during

hot pressing’, Sov. Powder Metall. Met. Ceram., 1979, 18, (5),

312–316.

240. R. Angers and M. Beauvy: ‘Hot-pressing of boron carbide’,

Ceram. Int., 1983, 10, (2), 49–55.

241. G. I. Kalandadze, S. O. Shalamberidze and A. B. Peikrishvili:

‘Sintering of boron and boron carbide’, J. Solid State Chem.,

2000, 154, 194–198.

242. B. Champagne and R. Angers: ‘Mechanical properties of hot-

pressed B-B4C materials’, J. Am. Ceram. Soc., 1979, 62, (3–4),

149–153.

243. K. Hirao, S. Sakaguchi, Y. Yamauchi, S. Kanzaki and S. Yamada:

‘Boron carbide based sintered compact and method for prepara-

tion thereof’, US patent no. 0 059 541 A1, 2005.

244. V. Skorokhod, Jr and V. D. Krstic: ‘High strength-high toughness

B4C–TiB2 composites’, J. Mater. Sci. Lett., 2000, 19, 237–239.

245. H. Hofmann and G. Petzow: ‘Structure and properties of reaction

hot-pressed B4C–TiB2–W2B5 materials’, J. Less Comm. Met.,

1986, 117, 121–127.

246. J. Deng, J. Zhou, Y. Feng and Z. Ding: ‘Microstructure and

mechanical properties of hot-pressed B4C/(W,Ti)C ceramic

composites’, Ceram. Int., 2002, 28, 425–430.

247. D. Jianxin and S. Junlong: ‘Microstructure and mechanical

properties of hot-pressed B4C/TiC/Mo ceramic composites’,

Ceram. Int., 2009, 35, 771–778.

248. S. Yamada, K. Hirao, Y. Yamauchi and S. Kanzaki: ‘B4C–CrB2

composites with improved mechanical properties’, J. Eur. Ceram.

Soc., 2003, 23, 561–565.

249. T. Vasilos and S. K. Dutta: ‘Low temperature hot pressing of

boron carbide and its properties’, Am. Ceram. Soc. Bull., 1974, 53,

(5), 453–454.

250. D. Jianxin: ‘Erosion wear of boron carbide ceramic nozzles by

abrasive air-jets’, Mater. Sci. Eng. A, 2005, A408, 227–233.

251. B. Mu, L. Tang, H. Zhang, W. Yan, T. Yin and T. Zhang:

‘Influence of the rare-earth oxide on the properties of boron

carbide ceramics’, Powder Metall. Technol., 2008, 26, (3), 187–191,

195.

252. B. Mikijelj, G. Victor and K. A. Schwetz: ‘Lightweight boron

carbide materials with improved mechanical properties and

process for their manufacture’, US patent no. 0 010 391 A, 2007.

253. T. Maruyama and S. Onose: ‘Fabrication and thermal conductiv-

ity of boron carbide/copper cermet’, J. Nucl. Sci. Technol., 1999,

36, (4), 380–385.

254. T. Jiang, Z. Jin, J. Yang and G. Qiao: ‘Investigation on the

preparation and machinability of the B4C/BN nanocomposites by

hot-pressing process’, J. Mater. Proc. Technol., 2009, 209, 561–

571.

255. T. Jiang, Z. Jin, J. Yang and G. Qiao: ‘Wear resistance of silicon

infiltrated B4C/BN composites’, Mater. Lett., 2008, 62, 4559–

4562.

256. S. Yamada, K. Hirao, Y. Yamauchi and S. Kanzaki: ‘Mechanical

and electrical properties of B4C–CrB2 ceramics fabricated by

liquid phase sintering’, Ceram. Int., 2003, 29, 299–304.

257. M. S. Koval’chenko, Yu. G. Tkachenko, V. V. Koval’chuk, D. Z.

Yurchenko, S. V. Satanin and A. I. Kharlamov: ‘Structure and

properties of hot-pressed boron carbide base ceramics’, Sov.

Powder Metall. Met. Ceram., 1990, 29, (7), 523–526.

258. C. H. Jung and S. J. Lee: ‘Machining of hot pressed alumina-

boron carbide composite cutting tool’, Int. J. Refract. Met. Hard

Mater., 2005, 23, 171–173.

259. B. Y. Yin and L. S. Wang: ‘Study on mechanical strength of the

hot-pressing sintered boron carbide’, Atom. Energy Sci. Technol.,

2004, 38, (6), 522–525.

260. www.atozofmaterials.com

261. B. Matchen and D. Robertson: ‘Boron carbide ballistic armour

modified with chromium and/or boron’, US patent no. 3 729 372,

1973.

262. S. Tuffe, J. Dubois, G. Fantozzi and G. Barbier: ‘Densification,

microstructure and mechanical properties of TiB2-B4C based

composites’, Int. J. Refract. Met. Hard Mater., 1996, 14, 305–310.

263. G. Petzow, H. Hofmann and K. Weiss: ‘Process for the

preparation of carbide-boride products’, US patent no. 4 670

408, 1987.

264. K. F. Cai, C. W. Nan, M. Schumecker and E. Mueller:

‘Microstructure of hot pressed B4C–TiB2 thermoelectric compo-

sites’, J Alloys Compd, 2003, 350, 313–318.

265. A. Li, Y. Zhen, Q. Yin, L. Ma and Y. Yin: ‘Microstructure and

properties of (SiC,TiB2)/B4C composites by reaction hot pressing’,

Ceram. Int., 2006, 32, 849–856.

266. J. H. Han, S. W. Park and Y. D. Kim: ‘Reaction synthesis and

mechanical properties of B4C-based composites’, Mater. Sci.

Forum, 2007, 534–536, 917–920.

267. M. Yokouchi: ‘Effect of Mo content on mechanical properties of

B4C(W,Mo)B2 hard material’, J. Jpn Soc. Powder Powder Metall.,

1999, 47, (1), 23–29.

268. M. Yokouchi: ‘Effect of B content on mechanical properties of

B4C(W,Mo)B2 hard material’, J. Jpn Soc. Powder Powder Metall.,

2001, 48, (7), 660–664.

269. O. N. Grigor’ev, V. V. Kovalchuk, O. I. Zaporozhets, N. D. Bega,

B. A. Galanov, E. V. Prilutskii, V. A. Kotenko, T. N. Kutran and

N. A. Dordienko: ‘Synthesis and physicomechanical properties of

B4C–VB2 composites’, Powder Metall. Met. Ceram., 2006, 45, (1–

2), 47–58.

270. P. A. D. S. L. Cosention, C. A. Costa, J. B. De Campos and R. R.

De Avillez: ‘Hot pressing of boron carbide using metallic carbides

as additives’, Ceram. Eng. Sci. Proc., 2008, 28, (5), 135–141.

271. D. Jianxin and S. Junlong: ‘Sand erosion performance of B4C

based ceramic nozzles’, Int. J. Refract. Met. Hard Mater., 2008,

26, 128–134.

272. T. Jiang, Z. Jin, J. Yang and G. Qiao: ‘Property and

microstructure of machinable B4C/BN nanocomposites’, Key

Eng. Mater., 2008, 368–372, (1), 936–939.

273. Z. Panek: ‘The synthesis of SiC-B4C ceramics by combustion

during hot-pressing’, J. Eur. Ceram. Soc., 1993, 11, 231–236.

274. J. J. Petrovic, K. J. McClellan, C. D. Kise, R. C. Hoover and

W. K. Scarborough: ‘Functionally graded boron carbide’, Ceram.

Eng. Sci. Proc., 1998, 19, (4), 387–393.

275. K. S. Singhal and B. P. Singh: ‘Sintering of boron carbide under

high pressures and temperatures’, Ind. J. Eng. Mater. Sci., 2006,

13, (2), 129–134.

276. T. L. Hans: ‘Hot isostatic pressing of ceramic powders to dense

ceramic parts’, Ind. Heat., 1984, 51, (1), 39–40, 42.

277. T. L. Hans: ‘Dense ceramic parts hot pressed to shape by HIP’,

Mater. Sci. Res., 1984, 17, 571–582.

278. P. Larsson, N. Axen and S. Hogmark: ‘Improvements of the

microstructure and erosion resistance of boron carbide with

additives’, J. Mater. Sci., 2000, 35, 3433–3440.

279. N. Cho, Z. Bao and R. F. Speyer: ‘Density-and hardness-

optimized pressureless sintered and pot-hot isostatic pressed B4C’,

J. Mater. Res., 2005, 20, (8), 2110–2116.

280. N. Cho: ‘processing of boron carbide’, PhD thesis, School of

Materials Science and Engineering, Georgia Institute of

Technology, Atlanta, GA, USA, 2006.

281. R. F. Speyer and E. A. Judson: ‘New process makes complex-

shaped armor a reality’, Am. Ceram. Soc. Bull., 2006, 85, (3), 21–

23.



Pub

lishe

d by

Man

ey P

ublis

hing

(c)

IOM

Com

mun

icat

ions

Ltd

282. K. A. Schwetz, W. Grellner and A. Lipp: ‘Mechanical properties

of HIP treated sintered boron carbide’, Inst. Phys. Conf. Ser.,

1986, 75, 413–426.

283. K. A. Schwetz, L. S. Sigl and L. Pfau: ‘Mechanical properties of

injection molded B4C-C ceramics’, J. Solid State Chem., 1997,

133, 68–76.

284. M. H. Bocanegra-Bernal: ‘Hot isostatic pressing (HIP) technology

and its applications to metals and ceramics’, J. Mater. Sci., 2004,

39, (21), 6399–6420.

285. F. Zimmerman and J. Toops: ‘Hot isostatic pressing (HIP)

technology’, Ind. Heat., 2006, 73, (8), 71–74.

286. T. Fujikawa, Y. Manabe, M. Yoneda, S. Kofune and T. Nakai:

‘Recent trends of HIP equipment technology in Japan’, ASME

Publ. PVP, 2004, 473, 27–31.

287. S. H. Yoo, K. M. Sethuram and T. S. Sudarshan: ‘Apparatus for

bonding a particle material to near theoretical density’, US patent

no. 5 989 487, 1999.

288. B. Klotz, K. Cho, R. J. Dowding and S. D. Sisson:

‘Characterization of boron carbide consolidated by the plasma

pressure compaction (P2C) method in air’, Ceram. Eng. Sci. Proc.,

2001, 22, (4), 27–34.

289. B. R. Klotz, K. C. Cho and R. J. Dowding: ‘Sintering aids in the

consolidation of boron carbide (B4C) by the plasma pressure

compaction (P2C) method’, Mater. Manuf. Process., 2004, 19, (4),

631–639.

290. N. Frage, S. Hayun, S. Kalabkhov and M. P. Dariel: ‘The effect

of Fe addition on the densification of B4C powder by spark

plasma sintering’, Powder Metall. Met. Ceram., 2007, 46, (11–12),

533–538.

291. Y. Kodera, N. Isibashi, T. Imai, T. Yamamoto, M. Ohyanagi,

U. Anselmi-Tamburini and Z. A. Munir: ‘Spark plasma sintering

of less-crystallized boron carbide with defects’, Ceram. Trans.,

2006, 194, 101–111.

292. C. B. Wang, S. Zhang, Q. Shen and L. M. Zhang: ‘Investigation

on reactive sintering process of boron carbide ceramics by XRD’,

Mater. Sci. Technol., 2009, 25, (6), 809–812.

293. S. Zhang, R. Yang, Q. Shen, C. B. Wang and L. M. Zhang:

‘Synthesis and densification of B-C ceramics by spark plasma

sintering’, J. Syn. Cryst., 2007, 36, (3), 672–674.

294. D. M. Hulbert, D. Jiang, U. Anselmi-Tamburini, C. Unuvar and

A. K. Mukherjee: ‘Experiments and modeling of spark plasma

sintered, functionally graded boron carbide-aluminum compo-

sites’, Mater. Sci. Eng. A, 2008, A488, 333–338.

295. Y. Ling, C. Ge, J. Li and X. Bai: ‘Processing and characterization

of B4C/Cu graded composite as plasma facing component for

fusion reactors’, J. Univ. Sci. Technol. Beijing, 2003, 10, (1), 39–43.

296. D. Agrawal: ‘Microwave sintering of metals’, Mater. World, 1999,

7, (11), 672–673.

297. A. Goldstein, R. Ruginets and L. Geifman: ‘Carbide matrix

composites by fast MW reaction-sintering in air of B4C–SiC–Al

mixtures’, Ceram. Int., 2008, 35, (3), 1297–1300.

298. I. Bogomol, T. Nishimura, O. Vasylikiv, Y. Sakka and P. Loboda:

‘Microstructure and high-temperature strength of B4C–TiB2

composite prepared by a crucibleless zone melting method’,

J. Alloys Compd, 2009, 458, (1-2), 677–681.

299. C. Zhang, X. Huang, Y. Yin, F. Xia, J. Dai and Z. Zhu:

‘Preparation of boron carbide-aluminum composites by non-

aqueous gelcasting’, Ceram. Int., 2009, 35, 2255–2259.

300. W. M. Goldberger, A. K. Reed and R. Morse: ‘Synthesis and

characterization of HSC silicon carbide’, Proc. Conf. Silicon

Carbide ’87, (ed. J. D. Cawley), 93–104; 1987, Westerville, OH,

The American Ceramic Society.

301. M. Steinbruck, A. Meier, E. Nold and U. Stegmaier:

‘Degradation and oxidation of B4C control rod segments at high

temperatures’, Institut fur Materialforschung, Programm

Nukleare Sicherheitsforschung, Forschungszentrum Karlsruhe

GmbH, Karlsruhe, Germay, 2004.

302. M. Steinbruck: ‘Oxidation of boron carbide at high temperatures’,

J. Nucl. Mater., 2005, 336, 185–193

303. H. Steiner: ‘Modelling of boron carbide oxidation in steam’,

J. Nucl. Mater., 2005, 345, 75–83.

304. R. Zehringer, H. Kunzli and P. Oelhafen: ‘Oxidation behaviour of

boron carbide’, J. Nucl. Mater., 1990, 176/177, 370–374.

305. D. Radev and Z. Zahariev: ‘Oxidation stability of B4C–MexBy

composite materials’, J. Alloys Compd, 1993, 197, 87–90.

306. O. N. Grigorev, T. V. Dubovik, N. D Bega, V. A. Kotenko, V. M.

Panashenko, V. I. Lyashenko, A. A. Rogozinskaya and L. I.

Chernenko: ‘Sintered ceramics based on boron nitride and

carbide’, Powder Metall. Met. Ceram., 2007, 46, (1–2), 46–50.

307. J. Rodel, A. B. N. Kounga, M. Weissenberger-Eibl, D. Koch,

A. Bierwisch, W. Rossner, M. J. Hoffmann, R. Danzer and

G. Schneider: ‘Development of a roadmap for advanced ceramics:

2010–2025’, J. Eur. Ceram. Soc., 2009, 29, 1549–1560.



Documents

Synthesis and Consolidation of Boron Carbide- A Review