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PRINCIPLES OF
CERAMICS
PROCESSING
Second Edition
JAMES
S
REED
New York State College of Ceramics
Alfred University
Alfred, New York
A Wiley-Interscience Publication
JOHN WILEY SONS, INC.
New York Chichester Brisbane Toronto Singapore
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This text
is
printed on acid-free paper.
Copyright
1995 by John Wiley Sons, Inc.
AIl rights reserved. Published simultaneously
in
Canada.
Reproduction
or
translation
of
any part
of
this work beyond
that permitted
by
Seetion
107 or 108 of
the 1976 Uníted
States Copyright Ael without the permission
of
the copyright
owner is unlawful. Requests for permission or further
information should be addressed to the Permissions Department,
John Wiley Sons, Inc., 605 Third Avenue, New York,
NY
10158-0012.
library 0 Congress CataJoging in Publication Data:
Reed, James Stalford, 1938-
Principies of ceramics processing I James S Reed.-2nd cd.
p cm.
Rev. cd. of: Introduction to lhe principies of ceramic processing.
1988.
A
Wiley-Interscience publicatíon."
Ineludes bíbliographical references and índex.
ISBN 0-471-5972 l-X
1
Ceramics.
I.
Títle.
II
Series: Reed, James Slalford, 1938
Introduclion to lhe principies of ceramíc processing.
TP807.R36 1994
666-dc20
94-20838
Printed in lhe Unitcd States of America
10 9 8 7 6 5 4 3 2 1
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PART II
CERAMIC RAW MATERIALS
ln studying ceramics processing
it is
necessary to be familiar with the types
of
r w
materiais available. Clay minerais which provide plasticity when mixed
with water; feldspar which acts as a nonplastic filler on forrning and a fluxing
liquid on firing; and sílica which is a filler that resists fusion have been the
backbone of the traditional ceramíc porcelains. Other silicate mineraIs are used
in
whitewares such as ceramíc tile therrnal shock-resistant cordierite products
and steatite electrical porcelains.
Silica aluminosilicates tabular aluminium oxide magnesium oxide cal
cium oxide and mixtures
of these mineraIs have long been used for structural
refractories. Alumina magnesia and aluminosilicates are now used in some
advanced structural ceramics. Silicon carbide and sílicon nitride are used for
refractory abrasive electrical and structural ceramics. Finely ground alumina
titanates and ferrites are the backbone of the electronic ceramics industry.
Stabilized zirconias are used for advanced structural and electrical products and
zircon zirconía and other oxides doped with transition and rare-earth metal
oxides are widely used as ceramic pigments. These materiais are commonly
prepared by calcining partic1e mixtures but some are now produced using
special chemícal techniques.
ln Chapter 3 the more common ceramic materiais produced
in
large tonnage
and widely used
in
ceramics are considered. Special materiais
of
exceptional
purity and homogeneity which are being developed for research and some very
advanced products are discussed
in
Chapter 4.
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CHAPTER 3
COMMON RAW MATERIALS
ln this chapter we briefly consider the nature o the starting materiaIs, tradi
tionally called raw materiaIs, that can be purchased from a vendor and received
at a manufacturing site. These materiaIs can vary widely
in
nominal chemical
and mineral composition, purity, physical and chemical structure, particle size,
and price. Categories o
raw materiais include
(1)
nonunjform crude
m a t ~ r i a l
froPlIlª ral deposits, (2)
r( fined
industrial mineraIs lhat have been benefiç,ͪted
til_remove m i n ~ a I i t n P u r i ~ É ' to sígnific3 ntly
i ~ r e a s e
the mineral purity ª. lJJ
p h y ' s i c a t ~ º l ' l s i s t t l . 0 , and (3) hjgh-tonnage industrial inorganic c h ~ _ r n i c ª l ~ J h ª t
llave
u l d e r g o n ~
extensive
c h e t n í ( ; _ ª L Q r º - t : ~ . s _ ~ Í l g . ª . 1 L ( n l 1 e m e n t
to significantly
~ g ~ . ' l < ~ ~ h e _ . chemical purityand i r n p ~ º - v ~ ~ h . e _ p.hysi.cª characterisliçs.
The c h o i ç ~ o f a raw material for a particular product wiI1 depend on material
~ o s t ,
t n - ª r k ~ f a c t ~ r s , '::.( ndor
~ e r y i c e s , technical processing 纺§jdera Í.Qns, and
t b ~ l l t i m a t e performance requirements and market price o the f i n i ~ h ~ r o d u c t
For products in which processing adds considerable dollar value, the cost o
the starting material
is
a relatively small component o the production costs.
Accordingly, a higher-quality and more expensive material may be acceptable
for microelectronics, coatings, fibers, and some high-performance products.
But the average cost
o
raw
materiais for building materiaIs and traditional
ceramics such as tile and porcelain must be relatively low. Cost-benefit con
siderations may suggest substitutions o materiaIs o lower cost that do nol
impair the quality, or altematively, a more expensive material, which may
be
more economically processed and/or which will increase the qualityand per
formance o the product.
5
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36
COMMON RAW MATERIALS
3.1
CRUDE M TERI LS
Many early ceramics industries were based near a natural deposit containing a
combination
of
crude minerais that could be conveniently processed into usable
produets. Construetion materiais such as brick and tile and some pottery items
are historical examples, and many are still identified by the regional name.
Some crude materiaIs are
of
sufficient purity to be used in heavy refraetories:
Crude bauxite, a nonplastic ore containing hydrous alumina mineraIs, clay
minerais, and mineral impurities such as quartz and feme oxides,
is
used in
producing some refractories. Today, however, most ceramics are produced
from more refined minerais.
3.2
INDUSTRI L MINER LS
Industrial minerais are used
in
large tonnages for producing construction ma
teriais, refraetories, whitewares, and some electrical ceramics. They are used
extensively as additives in glazes, glass, and raw materiais for industrial ehem
icals. Common examples are listed in Table 3.1.
Clays are produeed by the weathering
of
aluminosilieate roeks and sedi
mentation. Clay minerais are layer-type hydrous aluminosilíeates whieh ean be
\ e
~ 6 ' \ { o
TABLE 3.1
Starting
Materiais for Ceramics
P
,,-
c
Purity
Category (
Materiais
----------------------------- -------------------------
Crude materiais
Variable Shales, stoneware clay, tile ciay, crude
bauxite, crude kyanite, natural ball
clay, bentonite
Industrial minerais
85-98 Ball clay, kaolin, refined bentonite,
(99
quartz) pyrophyI1ite. tale, feldspar,
nepheline syenite, wollastonite,
spodumene, glass sand, potter s flint
(quartz), kyanite, bauxite, zircon,
rutile, chrome ore, caleined kaolin,
dolomite
Industrial inorganic
98-99.9
Calcined alumina (Bayer process),
chemicals
caleíned magnesia (from brines,
seawater), fused alumína, fused
magnesia, aluminum nítride, silícon
carbíde, silicon nitride, barium
carbonate, titania, calcined titanates,
iron oxide, calcíned ferrites,
zírconia, stabílized zirconia, calcined
zirconates
Special inorganic
>99.9
Various materiais (see Chapter 4)
chemicals
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INDUSTRI L MINER LS 7
dispersed into fine particles (Fig. 3.1). Kaolin is a relatively pure, white firing
clay eomposed principally
of
the mineral kaolinite I
2
Si
2
0s(OH)4 but contain-
ing other clay minerais, as indicated in Table 3.2, and a minor amount
of
impurity minerais sueh as quartz
Si0
2,
ilmenite
FeTi0
3, rutile
Ti02
and he-
matite Fe203 Ball day is a sedimentary clay of fine particle size eontaining
Fig. 3.1 Kaolin that is a) aggregated and b) dispersed into platelets.
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38 COMMON R W MATERIALS
T ABLE 3.2 Clay Minerais
Mineral
Ideal Chemical Formula
Kaolinite Alz(SizOs)(OH)4
Halloysite
A1
2
(Si
2
0s)(OH)4 .
2H
2
0
Pyrophyllite Alz{Si
2
0sh(OHh
Montmorillonite
(Ali 67Nau33Mgo33)(SizOs)z(OHh
Mica
A1
2
K(Si ,.sAlosOsMOHh
Illite
Al
2
xMg,K,-x-
Source: After W. D. Kíngery, lntroduction
t
Ceramics 1st ed., Wiley
Interscíence, New York, 1960.
complex organic matter ranging down to a submicron size. BentonÍte
is
a
complex clay containing a relatively high proportion of the clay mineral mont
morillonite. Clays are used
in
whiteware formulations and aluminosilicate re
fractories to produce plasticity
in forming and resistance to deformation when
partial fusion occurs during firing.
Other layer-type hydrous silicates are Mg
3
Si
4
0
IO
(OHh
and pY Qphyllite
AI
Si
4
0
IO
(OHh, which are used extensively in compositions for ceramic tile,
cordierite, and steatite porcelain. Commercial grades contain impurities such
as calcite CaCO) or dolomite (Mg,Ca)C0
3
and other mineral impurities that
depend on the source.
Crushed and milled quartz SiO
z
derived from relatively pure deposits
of
sandstone
is
a granular silicate mineral used extensively
in
whitewares, refrac
tories, and glaze compositions (Fig. 3.2). Eelds.Qars composed of the minerais
albite NaAlSi
3
0
g
and microcline or orthodase KAlSi
3
0 g and nepheline syenite
containing albite, microcline, and nephelite KosNa15(Al,Si)20g are the prin
cipal fluxes used
in
whitewares and silicate glazes. Wollastonite
CaSi0
3
is used
in
some tile compositions and glazes. Petatite
lIAlSi
4
0
lO
and spodumene
LiAlSi
2
0
6
are used as a secondary flux and to redu ce the thermal expansion
of
the fired material.
Chrome ores composed principally
of
a complex solid solution of spinels
(Mg,Fe)(AI,Cr,Feh04 and impurities such as dolomite and magnesium silicates
are used
in
combination with calcined magnesia MgO
in
basic refractories.
~ ~ l l ~ CaQ produced by calcining limestone
CaC0
3
and calcined dolo
mite (Ca, Mg)O is bonded with tar and used for lining basic oxygen steel
fumaces. Beneficiated kyanite
AI
2
SiO
s
, bauxite, and zircon SiZr04 are also
used in refractory compositions. Milled zircon is also used as an opacifier in
glazes and
in
producing zircon pigments and is a precursor for zirconia
Zr02'
Calcined kaolin (Fig. 3.2) is used as a nonplastic filler in refractory mixes and
mortars.
The beneficiation
of
industrial mineraIs begins with crushing and grinding
to a smãiT enough size t liberate undesired mineral phases. Further beneficia
tion may indude settling and flotation to segregate mineraIs
by
density or size,
the separation of magnetic minerais using powerful electromagnets, blending
of different processing runs for consistency, and perhaps particle size classifi-
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40
COMMON RAW MATERIALS
DragUne
Sllo\lel
Water
Portable
Blunger
Pump
Wet
Screening
~ r i t
J
Chemical
Leachingor
Magnetlc
Centrifugai
Claaaiflcatlon
Slurry
Blending
and Storage
Slurry
Irom
Other Deposita
Separation
l
Grit
Surlace
Modification
Rotary
Vacuum
Filtration
pron
Drying
Pulverizing
1
Slurry
Spray
Hopper
Bagging
Tank Car Drylng
Car
BOl Car
or Truck
Fig. 3.3 Processing flow diagram for the beneficiation
of
kaolin.
Concentrated soIids are usually dried using a rotary
or
belt dryer
or
by spray
drying. Some materiaIs are calcined, and a hard aggregate is fonned. Dried
cake or calcined materiaIs may be pulverized or ground and then sized or air
elutriated before bagging or loading in hopper cars. Many fine materiais are
loaded and unloaded using pneumatic ftuidization and are stored at the plant
site in large sílos.
3.3
INDUSTRI L INORG NIC CHEMIC LS
Important industrial ceramic chemicals include tabular and calcined aluminas,
magnesium oxide, silicon carbide, sílicon nitride, alkaline earth titanates, soft
and hard ferrites, stabilízed zirconia, and inorganic pigments. Extensive chem
ical beneficiation redu ces the content
of
accessary mineraIs and may increase
the chemicaI purity up to about 99.5 .
For
many materiaIs, the scale of op
eration is extremely Iarge, which aids in lowering the unit processing costs and
selling price.
Alumina AI
2
0
3
is the most widely used inorganic chemical for ceramics
(Table 1.2) and is produced worldwide in tonnage quantities for the aluminum
and ceramics industries using the Bayer processo The principal operations in
the Bayer process are the physical beneficiation of the bauxite, digestion (in
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INDUSTRIAL INORGANIC CHEMICALS
the presence of caustic soda NaOH at an eIevated temperature and pressure),
clarification, precipitation, and calcination, followed by crushing, milling, and
sizing (see Fig. 3.4). During the digestion, most of the hydrated aIumina goes
into soIution as sodium aIuminate:
ImpuritY SOlid) +
AI OHh solid)
+
NaOH solnl
(3.1)
Na+ solo) +
AI OH)4 solnl
+
ImpuritY sOlid)
and insoluble compounds of iron, silicon, and titanium are removed by settling
and filtration. After cooling, the filtered sodium aIuminate solution
is
seeded
with very fine gibbsite AI(OHh, and at the lower temperature the aluminum
hydroxide refonns as the stable phase. The agitation time and temperature are
carefully controlled to obtain a consistent gibbsite precipitate. The gibbsite
is
continuously classified, washed to reduce the sodium content, and then cal
cined. Material calcined at lIOO-1200°C is crushed and ground to obtain a
range of sizes (Fig. 3.5). Tabular aluminas are obtained by calcining to a higher
temperature, about 1650°C.
Magnesium oxide MgO of greater than 98% purity is prepared
by
precipi
tating magnesium hydroxide in a basic mixture of treated dolomite and natural
brines or seawater containing MgCl
2
and MgS
4
, followed by washing, filtra
tion, drying, and calcination.
Zirconia
Zr 2 of
99 purity is obtained by the caustic fusion
of
zircon
ZrSi
4
:
Chemical dissolving
of
the silicate
in
water simultaneously hydrolyzes the
sodium zirconate to hydrated zirconia. Zirconia is also produced
by
hot chlo
rination
of
zircon in the Presence of carbon, and the hydrolysis of the zirconium
tetrachloride product to fonn ZrOC1
2
• The ZrOCl
2
can be calcined directly
or
reacted with a base in water to fonn hydrous zirconia. Zircon may also be
dissociated to Zr 2 +
Si
2
by heating above 1750°C and the zirconium sep
arated by leaching with sulfuric acid:
Sílicon carbide SiC
is
produced in large tonnages using the Acheson process
by
reacting a batch consisting principally of high-purity sand and low-sulfur
coke at 2200-2500°C in an electric arc furnace.
Si
2
+
3C SiC
+
2CO gas)
(3.4)
The crystalline product is crushed, washed
in
acid and alkali, and then dried
after iron has been removed magnetically. Granular material is used
in
refrac
tories and bonded abrasives. Milled material chernically treated to remove
4
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I \ )
""
o
Fig. 3.4
The Bayer process for chemically refining bauxite into alumin
Inc., Pittsburgh, PA.)
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COMMON RAW MATERIALS
impurities introduced in millíng is used industrially for structural ceramics.
S i l i c o l ' t : l i ~ r i d e Si
3
N
4
is prepared by reacting silicon metal powder with nitrogen
or a mixture of silica and carbon powders with nitrogen at a high temperature:
(3.5)
Silicon nitride and aluminum nitride powders may be produced by the car
bothermal process:
3Si0
2
+ 6C + 2N
2
(gas)
---
Si
3
N
4
+ 6CO gas)
(3.6)
Al
2
0
3
+ 3C + N
2
(gas) --- 2AIN + 3CO gas)
(3.7)
Aluminum nitride
is
also formed by dírect nitridation:
2AI solíd) +
N
2
(gas) ---
2AIN
(3.8)
The oxynitride SIALON is produced by the reaction of mixed powders of
silicon nitride, aluminum nitride, and alumina at a high temperature; the re
action is
(3.9)
The production of mixed metal oxides for e1ectronic ceramics such as barium
titanate BaTi0
3
, ferrites such as M11o.sZ11o.sFez04 and BaFe12019, mixed metal
oxide resistors, and ceramic colors such as doped zirconia involves the batching
and reaction of industrial inorganic chemicals, as is shown for the ferrite in
Fig. 3.6. The concentration of chemical dopants is carefully controlled. Soluble
material
is
sometimes removed
by
filtering before drying. Precursor industrial
chemicals for these compounds are commonly powders finer than a few microns
in size. Barium carbonate BaCO} and titania
Ti0
2
are commonly used for
preparing the titanates, and manganese carbonate
MnC0
3
,
zinc oxide ZnO,
hematite Fe203, and barium carbonate for the ferrites.
Titania
Ti0
2
is produced by the sulfate or chio ride processo
ln
the sulfate
process, ilmenite
FeTi0
3
is treated wíth sulfuric acid at 150-180°C to form
the soluble titanyl sulfate
TiOS0
4
:
After removing undissolved solids and then the iron sulfate precipitate, the
titanyl sulfate is hydrolyzed at
90°C
to precipitate the hydroxide TiO(OH)z:
(3.11 )
The titanyl hydroxide is ca1cined at about
lOOO°C
to produce titania
Ti0
2
• ln
the chloride process, a high-grade titania ore is chlorinated in the presence of
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RAW
MATERIALS ORYING OVEN
VACUUM CONVEYOR
CYCLONE
COLLECTOR
DIAPHRAGM
SLURRY PUMP
~ - A
BALL MILL
FAN
FILrER
AIR
LURRY
FEED
T N ~
AIR
..
HEATER
+
PRODUCT
-
PROOUCT
CART
Fig. 3.6 Preparatíon
of
calcíned manganese zínc ferrite
~
and spmy dried powdcr for processing. [From E.J. Moytl,
est E/ec. Eng. 7, 3-11 (1963).]
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46 COMMON RAW MATERIALS
carbon at 900-1000°C and the chloride TiCI
4
fonned
is
subsequently oxidized
to
Ti0
2
•
Barium carbonate BaCO) is the primary source
of
barium oxide BaO for
ceramícs. Barite ore, nominally BaS04, is reduced at a high temperature to
barium sulfide BaS which
is
water soluble. The reaction
of
an aqueous sulfide
solution with sodium carbonate Na2C03
or
carbon dioxide CO
2
produces a
barium carbonate precipitate which
is
then washed, dried, and ground.
The commercial iron oxide hematite ex-Fe20) used for preparing ferrites is
producedfrorn tilé-tlíennal decomposition
of
hydrated ferrous sulfate FeS04 .
7H
2
0 or by the precipitation
of
hematite and goethite ex-FeZ03 . H
2
0 from an
oxygenated sulfate solutíon containing dispersed iron metal. The size and shape
of the ultimate crystals of FeZ 3 are very dependent on the pH, temperature,
time, and impurities during precipitation. Zinc oxide ZnO
is
produced by roast
íng a concentrate
of
the mineral sphalerite ZnS in air. Manganese carbonate
MnC0
3
is derived from manganese sulfate MnS04
When thennally reacting titanates and ferrites, the temperature, time, and
atmosphere musibe adequate pennlTdecomposition ofihe carbonate and
promote interditfusion
of
the reactants through the reaction product that may
be several microns
in
thickness (Fig. 3.7). The time dependence of the relative
amount x
of
reactant
A
of radius rA transfonned into reaction product is given
by the Carter equation:
Kt
[I
+
(z
l xf í3 + (z
1)(1
X 2í3
=
Z + 2(1
z) ---, (3.12)
rÃ
where K is the apparent rate constant and z is the volume
of
product fonned
from a unit volume of reactant A. * The effect of temperature T is commonly
as
Out
Mixed Powder
Reaction
Fig. 3 7 Model for mixed powder reaction when particles are well dispersed, indi
cating maximum diffusion length for reaction
is
controlled by radius of reactanl particle.
*H. Schmalzried,
Solid State Reactions,
Academic Press. New York, 1974.
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INDUSTRIAL INORGANIC CHEMICALS 7
expressed by the Arrhenius relation and
o
exp
T
(3.13)
where
o
is the limiting rate constant that depends on the diffusion path length
and
is
the apparent activation energy for diffusion. The reaction
is
a function
of
both time and temperature, but temperature has a greater influence on the
rate. The time for total reaction eliminating the reactants varies directly with
the maximum size of agglomerates
or
segregated material in the batch. When
reacting micron-size oxide powders, thermal processing at a temperature in
excess
of
1200°C is commonly requisite, as is shown in Fig. 3.8 for the
formation
of
spinel
MgA1
2
0
4
•
Q t h ~ r i n l 1 ' ) Q I ª ~ ~ , : : a r i a b l e s
affecting solid-state reactions during calcining are
the
º a r t i c l ~ ) ; i z e
distributions of the reactants, the mixedness of the reactants,
the comJX)sition and flowQLgases-l the depth
a n d t u r n . o v ~ Q f _ l . a t e . , i : l l ,
and
e n d - º 1 ~ f 1 1 i c
a ~ : t ~ ~ ~ ~ ~ r m i c e _ f f e c t s . Sintering during calcination produces par
100
75
*
c:
o
50
~
c:
I I)
(.J
c:
o
u
25
OL-____ ____
900 1000 1100 1200
1300
1400
Temperature OC)
Fig. 3 8 The fonnation of spinel MgAl
2
0
4
from the solíd-state reaction of micron
size MgO and
o:-AI
2
0]
powder as a function of the reactíon temperature for a constant
reaction time of 8 h.
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SUGGESTED READING
Radiation
! ! ! ! !
Hot Gas Flow .....
Mlxlng
r--.. ....:.. ...-<c
l :><r<o I>
- T ra n ala
tlon
Refractory
Support
Thermal
Conductlon
Fig. 3.10 Thermal transport, gas flow, and particle movement during rotary calcina
tion and solid-state reaction.
SUMM RV
Few ceramics are produced today using crude raw materiais. Industrial minerais
are refined physically to reduce the concentration of undesirable mineral im
purities and to produce a particular particle size distribution; water-soluble
impurities are removed by washing. Industrial inorganic chemicals used to
produ ce the majority of technical ceramics are chemically processed on a large
scale to improve both the chemical and the mineral purity; the calcined product
containing hard aggregates is commonly milled to disperse the aggregates and
obtain a product
of
controlled size distribution. Mixed-oxide industrial chem
icals are commonly produced by calcining a mixture of these industrial chem
icals. The completeness
of
the reaction and unifonnity
of
the product depend
on the particle size and mixedness of the reactants and the time, temperature,
and atmosphere and their unifonnity during calcination. Different lots
of
pro
cessed materiais are blended to maintain a higher levei
of
unifonnity.
SUGGESTED RE DING
1.
Magnus Ekelund and Bertil Forslund, "Carbothermal Preparation
of
Silicon Ni
tride: Influence of Starting Material and Synthesis Parameters," J Am. Ceram.
Soc. 75(3), 532-539 (1992).
2. Julie M. Schoenung, "Analysis
of
the Economics
of
Silicon Nitride Powder Pro
duction,
Am. Ceram. Soco Buli. 70(1), 112-116 (1991).
3. Martin R. Houchin, David H. Jenkins, and Hari N. Sinha, "Production
of
High
Purity Zirconia from Zircon, " Am. Ceram. Soco Buli. 69(10),1706-1710 (1990).
4.
L.
D. Hart, Alumina Chemicals The American Ceramic Society, Westerville, OH,
1990.
49
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50 COMMON RAW MATERIALS
5.
H. Okada, H. Kawakarni, M. Hashiba, E. Miura, Y. Nurishi, and T. Hibino,
"Effect of Physical Nature
of
Powders and Firing Atrnosphere on ZnAI
2
0
4
For
rnation," J.
Am. Ceram. Soe.,
68(2), 58-63 (1985).
6. Materiais o Advaneed Ceramies and Tradítíonal Ceramics, Cerarnic Industry
Magazine, Corcoran Publishers, Solon, OH, 1985.
7.
Proeess Míneralogy o Ceramic Materiais, Wolfgang Baurngart et aI., Eds., EI
sevier, New York, 1984.
8. Kirk-Othmer, Eneyclopedia o Chemieal Teehnology, Wiley-Interscience, New
York, 1983.
9. Betty L Milliken, "Color Control in a Pigrnent Manufacturing
Plant,"
Am. Ce
ramo
Soe. Buli., 62(12), 1338-1340 (1983).
10. T. Nornura and T. Yarnaguchi, "Ti0
Aggregation and Sintering of BaTiO] Ce
rarnics,"
Am. Ceram. Soe. Buli.,
59(4), 453-455, 458 (1980).
II. F. H. Norton, Fine Ceramies, Krieger, Malabar, FL, 1978.
12. W.
D. Kingery, H.
K.
Bowen, and D. R. Uhlrnann,
Introduetion 10 Ceramics,
2nd ed, Wiley-Interscience, New York, 1976.
13.
W. E. Worrall, Clays and Ceramie Raw Materiais, Halsted Press Div., Wiley
Interscience, New York, 1975.
14. Rex W. Grirnshaw, The
Chemistry and Physies
o
Clays and Other Ceramie Ma
t e r i a L ~ Wiley-Interscience, New York, 1971.
15.
Annual Ceramie Industry Data Book, Cahners, Boston, MA.
16.
Ceramic Source,
Arnerican Cerarnic Society, Colurnbus, OH.
PROBLEMS
3.1
Categorize the materiais in the following pairs of starting materiais as
crude material, industrial mineral,
or
industrial inorganic chemical and
expIain your assignment: bauxite-Bayer process alumina, kaolin-calcined
kaolin, calcined alumina-calcined kaolin, silicon carbide-silicon nitride,
and titania-barium tÍtanate.
3.2 When fonning a compound by a solid-state reaction, does the completion
of
the reaction depend on the average or the maximum particle size?
Explain. Does the aggregation
of
the starting materiais influence the re
action?
3.3 Write the chemical reaction for the hydrolysis
of
sodium zirconate which
folIows the reaction in Eq.
(3.2).
3.4 State several reasons why a pigment calcined in an open crucible in a
gas-fired kiln may differ in color from the sarne pigment batch fired in a
closed sagger in an electric fumace.
3.5
Construct a processing f10w diagram for the formation
of
BaTiO) powder.
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EXAMPLES
3.6
Why are hard powder aggregates commonly formed in a solid-state re
acted batch of material?
3.7 Calculate the amount
of BaC0
3
and
Ti0
2
required to produce 1 kg
of
BaTi0
3
·
3.8 Calculate the amounts of
Si0
2
, C
and N
2
required to form 1 kg of SbN
4
.
3.9
Write the nominal reaction equation for the formation of doped barium
titanate Bal xMxTi03 on heating a mixture of BaC0
3
•
MS0
4
• and Ti0
2
powders. Illustrate the diffusion paths.
3.10 Substitute the Arrhenius relation into the Carter equation and comment
on the dependence
of
amount reacted on increasing time and increasing
temperature.
3.11 Make a sketch similar to Fig. 3.7 for the formation
of
ZnFe204 from the
reaction
of
Fe203 and ZnO.
EXAMPLES
xample
3 1
Contrast the mineralogícal structure of the kaolin and mont
morillonite families
of
clay minerais.
Solution The kaolin minerais include kaolinite, nacrite, dickite, and halloy
site, and kaolinite is the most abundant and important. The kaolin minerais are
two-Iayer mineraIs. The disilicate layer with the composition Si
2
0
S
has Si
tetrahedrally coordinated with
O
bonds. The second layer has the composition
AI
2
(OH)6 and is called the gibbsite layer. The
AI
atoms are octahedrally co
ordinated with
O
bonds common to both layers and -OH within the layer.
Partial substitution of AI
H
for Si
4
in the octhedral layer and Mg
2
and Fe
2
in the tetrahedral layer commonly occurs when formed and the basal plane is
negatively charged. Chemisorbed alkalis and
Ca2+
occur for charge neutrality.
The resultant octahedrallayer is distorted and this weakens the bonding between
the structural units. Slight differences of the stacking of the units produces the
particular types of clay minerais.
The montmorillonites are three-Iayer minerais having a gibbsite sheet sand
wíched between two disilicate layers. The parent mineral is pyrophyllite. Iso
morphous cation substitution produces related minerais. Partial substitution of
Mg
2
for
A1
3
in
the octahedrallayer with surface adsorbed alkali for charge
neutrality produces montmorillonite. One-fourth substitution of AI
H
for Si
4
in the tetrahedral layer causes the surface alkali to e strongly bonded, and the
material mica is produced. Significant substitution in both layers, as is indicated
in
Table 3.2, produces the mineral iIIite. When Mg
2
completely replaces AI
H
in the gibbsite layer, the mineral is talco
5
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52 COMMON
R W
MATERIALS
~
E
Water
'arers
o
c1
O ~ 1 4 1
~ I ~ 1 1 1 y;tl oo
~ 1 1 5
o \
~
I
J - ~
.
aOo ~
d ~ D
H a f l o y ~ . t e
MOOimçr O'-'ite
Ch one
Hyórated) (Hydril ed}
@(OH) () Si-AI
l i)
AI-Mg
Example 3.1 Layer structures of clays and related mineraIs (spacing indicated is in
angstroms). [From W. D. Kingery, H.
K.
Bowen, and D. R. Uhlmann, lntroduction
t Ceramics
2nd ed., Wiley-Interscience, New York, 1976; after
R
E. Newnham and
G
W Brind1ey,
Acta Cryst. 9
759-764 (1956); 10, 88 (1957).]
fx mple 3.2
Compare and contrast the processing
of
ceramic grade sílica
and Bayer process aIumina.
Solution The operations
of
crushing, grinding, and classification are invoIved
in the production
of
both materiaIs. The big difference in the processing
of
the
alumina is major chemical refining: the chemicaI dissoIving
of
the aluminum
constituents
of
the bauxíte, the chemical precipitation
of
gibbsite, the washing
of the precipitate, and the calcination
of
the precipitate in the Bayer processo
fx mple 3.3
Explain why the dispersion of aggregates and aggIomerates in
reactant materiais and the uniform mixing
of
reactants are essentiaI
to
obtain a
uniform product from a solid-state reaction technique.
Solution As is indicated by the Carter equation and Fig. 3.7, the time to
produce a particular amount
of
reaction product depends directly on
r K
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EXAMPLES 5
Dispersion
of
aggregates will reduce the maximum reaCtant size r
A
which is
especially important because the dependence is on the square
of
the size. In-
creasing temperature increases the rate constant
K.
A higher temperature or time will be required to complete the reaction in
poorly mixed microscopic regions where the effective
rA
is large. Aggregate
in
precursors may not be completely reacted and may have a different grind-
ability than the majority of the product.