Classification of ceramics

What a ceramic is ?

From Greek word “keramos” (pottery, potter’s clay)

Inorganic nonmetallic materials obtained by the action of heat and subsequent cooling

Polycrystalline materials, single phase or multiphase (composites), sometimes with an amorphous component (glass)

Traditional ceramics

•Whitewares: tableware, cookware, sanitary ware, etc.•Refractories (kiln and furnace linings for steel and glass industry)•Structural clay products (floor & roof tiles, bricks, etc.)

Fabricated from clay, quartz, feldspar (earthenware) and kaolin (porcelain)

Technical/advanced ceramics

•Structural ceramics (mechanical properties: strength, toughness, hardness, creep resistance)•Functional ceramics (electric, magnetic, optical properties)

Structural ceramics

•Si3N4: bearing balls, cutting tools, heat exchangers, turbocharger rotors, parts of

gas turbines

•SiC: abrasives, disk brakes, pipes for corrosive liquids, ballistic armors

•WC, Ti(C,N): cermets, inserts for cutting tools

•B4C: neutron absorber in nuclear plants, ballistic armors, nozzles, abrasives

•Al2O3 (alumina): spark plugs, substrates, crucibles, furnace tubes, ballistic armors,

thermal insulation

•3Al2O3•2SiO2 (mullite) & Mg2Al3(Si5AlO18) (cordierite): catalytic converters, ceramic

filters

•ZrO2 (zirconia): knifes, watch cases, orthopedic implants, grinding media, thermal

barrier coatings

•UO2: nuclear fuel

•Ca10(PO4)6(OH)2 (hydroxyapatite): biomedical implants, artificial bone

Ceramic Si3N4 bearing parts

Radial rotor made from Si3N4 for a gas turbine engine The Porsche Carrera GT's

silicon carbide disk brake

Two Kyocera ceramic knives Ceramic body armour plates

Functionality Material Applications

Resistors SiC, MoSi2, LaCrO3 Heating elements for high temperature furnaces

Thermistors

(NTCR & PTCR)

Spinels

BaTiO3

Temperature sensors, self-regulating heating elements

Dielectrics with very low losses (r = 3 -10)

Al2O3, AlN, cordierite

Substrates for electronic circuits and chip packaging

Dielectrics for microwave applications (r = 30-80)

BaTi4O9, Zr(Ti,Sn)O4, BaMg1/3Ta2/3O3,

(Ba,Sr)TiO3,

MW resonators, filters and antennas for mobile communications and GPS devices, tunable MW devices

Temperature stable dielectrics (r 100)

CaTiO3, BaO-Nd2O3-TiO2

Capacitors with temperature-independent capacitance

Dielectrics with very high dielectric constant (r 3000)

BaTiO3 Multilayer ceramic capacitors

Piezoelectric ceramics Pb(Zr,Ti)O3 (PZT) Transducers, actuators and resonators

Pyroelectric ceramics Pb(Zr,Ti)O3 IR radiation detection and imaging

Functional ceramics

Functionality Material Applications

Ferroelectric ceramics

Pb(Zr,Ti)O3

SrBi2Ta2O9

Ferroelectric memories (FeRAMs)

Electrostrictive ceramics

PbMg1/3Nb2/3O3 -PbTiO3 (PMN-PT)

Actuators

Magnetic ceramics Spinels (Ni,Zn)Fe2O4

BaFe12O19

Y3Fe5O12 (YIG)

Inductors

Permanent magnets

Microwave devices (radars)

Ionic conductors Y:ZrO2 (YSZ)

Gd:CeO2

β-alumina

Electrolytes for solid-oxide fuel cells (SOFCs), oxygen sensors

Na-Batteries

Superconductors YBa2Cu3O7-x (YBCO)

MgB2

Superconducting cables for magnets

Transparent ceramics

Al2O3, MgAl2O4, Y3Al5O12 (YAG)

Phosphors, optical materials for lenses and laser systems, nose cones for heat-seeking missiles, high-pressure sodium street lamps

Optoelectronic materials

LiNbO3

PLZT

Waveguides, frequency doublers, voltage-controlled optical switches, modulators

Functional ceramics

Thick (left) and thick (right) substrates (alumina)

Pressed and extruded parts (alumina, mullite, zirconia)

Ferrites cores Microwave dielectric components

Microstructure of ceramics

Ceramic microstructures

SSS 99% Al2O3 – transparent fully dense (“ideal”) ceramic: grains + grain boundaries

SSS 99% Al2O3 - ceramic with residual porosity: grains + g.b. + pores

LPS 96% Al2O3 - dense ceramic with grain boundary glass phase: grains + glassy phase (CaO*SiO2) + 2 types of g.b.

Microstructural variables

Density - crystallographic (from unit cell parameters)- theoretical (zero porosity, takes into account real composition)- apparent (geometrical) density (< theoretical)- relative density = (apparent/theoretical)*100

Porosity- closed (only closed above 93% r.d.)- open (pore networks connected to the surface)- intragranular- intergranular

Grain size (simplest method: mean intercept length) Grain size distribution (monomodal, bimodal, abnormal grain growth) Grain shape (equiaxed, elongated, prismatic, columnar, tabular, platelets)

- aspect ratio (ratio longest/shortest size dimensions)

Extended defects (dislocations, stacking faults, twins, domain walls)

Second phase composition, shape and distribution

Texture (grains oriented in a preferential direction)

Intergranular porosity

Intragranular porosity

Y2O3:ZrO2 (PSZ) ceramicIntra- and intergranular porosity

Ba(Ti,Ce)O3 ceramicClosed (intragranular) and open (itergranular channels) porosity

Types of porosity

Equilibrium shape of grains. Hexagons (2D) and truncated octahedron (3D)

gb

gbgb

120°

Shape of grains and pores

Concave pore Convex pore Irregular pore associated with a hard agglomerate

Grain size distributions and abnormal grain growth

1450°C/2 hEquiaxed grains with monomodal distribution

1500°C/2 hSome large elongated grains appear: onset of AGG

1550°C/2 hBimodal distribution related to AGG

Mg0.1Al1.8Ti1.1O5 ceramics

FractographyPolished surface

Cross-sections of Ba(Ti,Zr)O3 ceramics

Grain pull-out

Revealing microstructure

Chemical etching

Si3N4

Fully-dense alumina

Thermal etching

SiC

Revealing microstructure

Er-doped BaTiO3

Solid grain Solid grain

Vapour

After polishing

After thermal treatment

Coated Co:WC:Ti(C,N) cermets

Optical microscopy in polarized light

Revealing microstructure

Spectrum In stats. O Ti Ba Ce Total 1 Yes 23.43 9.37 58.72 8.48 100.00 2 Yes 22.41 2.77 41.71 33.11 100.00

Scanning electron microscopy using backscattered electrons (BEI)

Al2O3-(Zr,Y)O2 compositeThe darker phase is alumina

Ba(Ti,Ce)O3 ceramic containing Ce-rich inclusions

Secondary phases in Er-doped BaTiO3

White phase: Er2Ti2O7

Dark gray phase: Ba6Ti17O40

Revealing microstructure