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C L Y M I N E R L S I N T H E C E R M I C I N D U S T R I E S

by

T~OMAS W. SMOOT

Harbison-Walker Refractories Company, Garber Research Center,

Pittsburgh, Pennsylv~nla

ABSTRACT

Th0 physical, chemical and mineralogical characteristics of clays used in the ceramics

industries are briefly outlined. Clays used include ball clays, fireclays, high-alumina

clays of the diaspore and burley types, and three-layer types. The high temperature

phases and bonding characteristics are briefly reviewed as are the uses of these various

clays in the structural clay products, whitewares and refractories.

The importance of clays in the past for ceramics and, in particular, refractories is

reviewed and evaluated for future importance.

I N T R O D U C T I O N

The ceramic industries are the major users of clay. These industries used

about 70 percent of all clays marke ted in the crude or beneficiated form and

those marketed only as finished products

M inerals Yearbook,

1950-1958).

For convenience, this discussion will be based on three majo r divisions of the

ceramic industry, namely (1) structural clay products, (2) whitewares, and

(3) refractories. These three divisions depend primarily on clay as a major

raw material although other ceramic industries do use clays.

It is the purpose of this paper to outline the uses of the various clays

employed in these major divisions and briefly to characterize the clays

physically, chemically and mineralogically. An overall evaluation of the

industry-wide trends, particularly as related to the relative importance of

clays, is att empted.

I would like to acknowledge the advice and guidance given by the following

members of the Harbison-Walker Staff: J. Spotts McDowell, now retired;

H. G. Wilcox, qual ity control; and D. O. McCreight, Garber Resea rch Center.

S T R U C T U R A L C L A Y P R O D U C T S

The structural clay produc ts are in part referred to by the Bureau of Mines

as

heavy clay products

and include: (1) building brick, (2) sewer pipe, (3) drain

tile, (4) conduits, (5) structural tile, (6) lightweight aggregate, and (7) light-

weight clay block, as well as other products. Traditionally, many products

such as architectural ter racott~ and paving brick have been included in such

309

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31 TENTH NATIONAL CONFERENCE ON CLAYS AND CLAY MINERALS

p r o d u c t l i st s b u t t h e y n o w s e em t o b e a p a r t o f t h e h i s t o r y o f t h e i n d u s t ry .

M o s t o f t h e s e p r o d u c t s a r e s h a p e d b y a n e x t r u s i o n m e t h o d a l t h o u g h

r e l a t i v e l y fe w o f t h e m a r e p r e ss e d , h a n d - m o l d e d o r m a r k e t e d u n s h a p e d t o b e

i n c l u d e d i n o t h e r p r o d u c t s .

T h e c l a y s u s e d i n t h e s e p r o d u c t s c o v e r a w i d e r a n g e o f c h e m i c a l, p h y s i c a l

a n d m i n e r a lo g i c a l p r o p e r ti e s . O n e t h i n g t h a t a ll m u s t h a v e in c o m m o n ,

h o w e v e r , i s t h a t t h e y m u s t b e e a s i l y a c c e s s i b l e . I n a n y g i v e n a r e a , t h e

a c c e ss ib i l i ty o f a d e p o s it m a y p r o v e a l m o s t a s i m p o r t a n t a s th e b a s ic r e q u ir e -

m e r i t s r e g a r d i n g c h e m i c a l a n d p h y s i c a l p r o p e r t i e s .

V e r y f e w r e st r i c ti o n s a r e p l a c e d o n d e p o s i t s c o n s i d e r e d f o r u s e in t h e s e

p r o d u c t s . P r o b a b l y t h e m o s t i m p o r t a n t i s t h a t t h e c l a y be su i t ab l e fo r f o r m -

i n g . B r i e f l y l i s t e d b e l o w , i n d e c r e a s i n g o r d e r o f i m p o r t a n c e , a r e t h e s p e c if i ca -

t i o n s w h i c h , i d e a l l y , s h o u l d b e m e t b y r a w m a t e r i a l s u s e d i n m o s t s t r u c t u r a l

c l a y p r o d u c t s .

1. P l a s t i c e n o u g h f o r s h a p i n g

2 . D r y w i t h o u t e x c es si v e c r a c k in g a n d w a r p i n g

3 . H a v e l o w a n d w i d e v i t r i f ic a t i o n r a n g e

4 . L o w c a r b o n a t e c o n t e n t

5 . H a v e a s p r e a d i n p a r t i c l e s iz e

6 . C o n t a i n n o n - c l a y c o n s t i t u e n t s

T h e f i r s t t w o r e q u i r e m e n t s a r e s e l f - e x p l a n a t o r y . T h e l o w a n d w i d e

v i t r i f i c a t i o n r a n g e i s d e s i r a b l e f o r f a v o r a b l e u n i t f i r i n g c o s t a n d f o r e a s e o f

f ir in g . T h e l o w c a r b o n a t e c o n t e n t i s d e si r a b le f o r t w o r e a s o n s : 1 ) t h e f l u x i n g

a c t i o n o f c a r b o n a t e s t e n d s t o s h o r t e n t h e f ir in g r a n g e o r c a u s e l o c a li z e d f lu x

s p o t s a n d 2) C a O a n d M g O re s u l ti n g f r o m f ir in g o f c o m m o n c a r b o n a t e - b e a r -

i n g c l a y s w i l l h y d r a t e r a t h e r e a s i l y w i t h r e s u l ti n g d i s r u p t i o n t o t h e f i re d

p r o d u c t .

A s p r e a d i n p a r t i c l e s i z e t e n d s t o w i d e n t h e v i t r i f i c a t i o n r a n g e a n d a l s o

g e n e r a ll y p r o m o t e s a s t ro n g e r t e x t u r e t h a n is f o u n d i n a c l a y t h a t h a s a

n a r r o w r a n g e o f p a r t i c l e si ze s. T h is , e s p e c i a ll y i n c o n j u n c t i o n w i t h t h e n e x t

p o i n t a b o u t n o n - c l a y m i n e r a l s su c h a s q u a r tz , i s p a r t i c u l a r l y i m p o r t a n t i n

e x t r u d e d s h a pe s . I n a m i x c o n t a in i n g a g r e a t p r e d o m i n a n c e o f t w o - d im e n -

s i o n a l f la k y ) p a r t i c le s w i t h n e a r l y t h e s a m e p a r t ic l e s iz e , a f o r m i n g p r e s s u r e

m i g h t o r i e n t t h e p a r t i c l e s so t h a t p a r a l l e l z o n es o f w e a k n e s s w o u l d r e s u l t. I f

a r a n g e o f p a r t i c l e s iz e s i s a v a i l a b l e i n t h e c l a y f r a c t i o n a n d a v a r i e t y o f

t h r e e - d i m e n s i o n a l s h a p e s a r e s u p p l i e d b y n o n - c l a y m a t e r i a l s , t h e n t h e s e

p a r a l l e l p a t t e r n s a r e g e n e r a l l y d i s r u p t e d a n d a c l o s e -k n i t t e x t u r e i s f o r m e d

w h i c h i s e q u a l l y s t r o n g i n a l l d i r e c t i o n s .

I f t h e s a l e a b le p r o d u c t i s o n e t h a t d e p e n d s i n p a r t u p o n f i re d co l or , t h e n

e x c e ss iv e a m o u n t s o f i ro n c o m p o u n d s i n t h e c l a y a re h a r m f u l . T h i s i s o f

p a r t i c u l a r i m p o r t a n c e i n o n l y a f e w p r o d u c t s s u c h a s f ac e t il e a n d , t o a c e r t a i n

e x t e n t , f a c e b r i c k .

F r o m t h e s e q u a l i fi c a ti o n s , it i s a p p a r e n t t h a t a w i d e v a r i e t y o f m i n e r a l

a s s e m b l a g e s w i ll su ff ic e. E v e n s h a le s r ic h i n r e l a t i v e l y n o n p l a s t i e a n d i m p u r e

i ll it e s a n d c h l o ri te s , i f t h e y c o n t a i n e n o u g h n o n - c l a y m i n e r a l s a n d a r e

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CL Y ~V[INER LS IN TttE CER MIG INDUSTRIES

311

s u f fi c ie n t ly p l a s t i c f o r s h a p in g , a r e e m p l o y e d i n s t r u c t u r a l c l ay p r o d u c t s .

S u r f a c e d e p o s it s , e v e n t il l , w h i c h m i g h t c o n t a i n a h o d g e - p o d g e o f cl a y m i n e r a l s

i n c l u d i n g m o n t m o r i l l o n i t e s , a r e p r o f i t a b l y u s e d ( 1~ . E . G r i m , p e r s o n a l

c o m m u n i c a ti o n ) . S u c h c la y s c o m m o n l y h a v e l o w a n d c o m p a r a t i v e l y w i d e

v i t r if i c a t io n r a n g e s w i t h a l k a li c o n t e n t s i n e x c e ss o f 5 p e r c e n t . S u c h m i n e r a l

a s s e m b l a g e s c o m m o n l y a r e p l a s t i c e n o u g h f o r f o r m i n g a n d a r e e a s i l y f i r e d .

I f t h e c l a y i s c h a r a c t e r iz e d b y c o n s i d e ra b l e b l o a t i n g u p o n f ir in g , i t c a n b e

u s e d f o r m a k i n g l i g h t w e i g h t a g g r e g a t e . S l ig h t b l o a t i n g c a n b e t o l e r a t e d i n t h e

c l a y s a s c a n a p p r e c i a b l e f i r in g s h r i n k a g e i f t h e s e t e n d e n c i e s c a n b e o f f s e t b y

a d d i t i o n o f n o n - c l a y m i n e r a ls t o t h e m i x .

I n r a r e c a s es , p l a s t i c i z e r s s u c h a s b a l l c l a y o r c e r t a i n m o n t m o r i l l o n i t e c l a y s

o r p l a s t i c i z i n g c h e m i c a l a d d i t i o n s c a n b e p r o f i t a b l y b l e n d e d w i t h l o c a l l y

a v a i l a b l e h a r d c l a y s t o i n c r e a se w o r k a b i l i t y . T h i s c a n o n l y b e j u s t if i e d ,

h o w e v e r , i f t h e c o s t o f p u r c h a s e , s h i p p i n g a n d b l e n d i n g i s s t il l l es s e x p e n s i v e

t h a n t h e c o s t o f i m p o r t i n g f i re d p r o d u c t s i n t o a n a r e a .

I n s u m m a r y t h e n , a t r e m e n d o u s r a n g e o f p h y s i c a l a n d c h e m i ca l p r o p e r t i e s

c a n b e t o l e r a t e d i n c l a y s u s ed b y t h e s t r u c t u r a l c l a y i n d u s t r y .

T H E W H I T E W A R E S I N D U S T R I E S

F o r t h i s d is c u ss io n , t h e w h i t e w a r e s i n d u s t r i e s a r e c o n s i d e r e d t o p r o d u c e

s u c h p r o d u c t s a s d i n n e r w a r e , s a n i t a r y w a r e , e l e c t r ic a l p o r c e l ai n , f lo o r a n d

w a l l t il e , a r t p o t t e r y , s p a r k p l ug s , a n d c h e m i c a l a n d r e f r a c t o r y p o r c e l ai n , a s

w e ll a s m a n y o t h e r p ro d u c t s . T h i s m a j o r d i v is io n c o n t a in s p r o d u c t s f o r m e d b y

a w i d e v a r i e t y o f m e t h o d s i n c l u d in g s l ip c a s t in g , j ig g e r in g , e x t r u d i n g , p o w e r

p r es si n g a n d h a n d m o l d i n g . M o st o f t h e p r o d u c t s m u s t b e m a d e f r o m w h i t e-

b u r n i n g m a t er ia l s. T h e g r e a t v a r i e t y o f p r o d u c t s , t h e i r v a r i e t y o f f o r m i n g

m e t h o d s , a n d s e rv i c e c o n d i ti o n s f o r t h i s d i v i s io n , a s s u re t h a t t h e r a w m a t e r i a l s

r e q u i r e m e n t s v a r y g r e a t l y , a l t h o u g h t h e y a r e li k e l y t o b e h i g h l y e x a c t i n g f o r

a n y g i v e n p r o d u c t .

M o s t o f t h e s e p r o d u c t s a r e c o m p o s e d o f a m i x t u r e o f k a o l in , b a l l c l a y a n d

g r o u n d n o n - c l a y m a t e r i a l s i n c l u d in g f e l d s p ar , q u a r t z , t a l c a n d o t h e r s. H i g h e r

a l u m i n a m a t e r i a l s s u c h a s k y a n i t e a n d s p e c i a l l y t r e a t e d k a o l i n s a r e b e in g

i n c o r p o r a t e d in s o m e o f t h e w h i t e w a r e p r o d u c t s s u c h a s ra d o m c s a n d e le c -

t r i c a l a n d r e f r a c t o r y p o rc e l ai n s . T h i s i n d u s t r y u s e s a b o u t t w o - t h i r d s o f a l l

d o m e s t i c a n d i m p o r t e d b a ll c l ay s , e v e n t h o u g h t h e y a r e u s ed o n l y i n p r o p o r -

t i o n s n e c e s s a r y t o p r o m o t e p l a s t i c i ty . T h e im p u r i t ie s , b o t h c h e m i c a l a n d

m i n e r a l o g i c a l , w h i c h a r e a l w a y s p r e s e n t i n b a l l c l a y s d i s c o u r a g e t h e i r u s e i n

e x c e s s i v e q u a n t i t i e s ( M e N a m a r a , 1 9 49 , p . 4 7 5 ) . B a l l c l a y s a r e n e c e s s a r y in

m o s t w h i t e w a r e s t h a t a r e c a s t b e c a u s e t h e y a r e r e a d i l y d i s p er s e d i n s l ip s ;

a n d i n m o l d e d p r o d u c t s t h e y a r e n e c e s s a r y f o r p l a s t i c i t y .

A l t h o u g h a c e r t a i n a m o u n t o f m o n t m o r i l l o n i te is g e n e r a ll y fo u n d i n b a h

c l ay s , t h e p r o p o r t i o n r a r e l y e x c e e d s 1 0 p e r c e n t . I n s o m e c as es , h o w e v e r ,

s o d i u m - m o n t m o r i ll o n i te s re p o r t e d l y h a v e b e e n a d d e d u p t o 15 p e r c e n t t o

o t h e r w i s e l o w p l a s t i c w h i t e w a r e m i x e s t o i n c r e a s e p l a s t i c i t y ( P o l u c k t o v a , 1 96 0,

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3 12 T ENT I I A T I O N A L C O : NF E R EN C E O N C L A Y S A N D C L A Y M I N E R A L S

p . 1 1 4). I t m u s t b e a s s u m e d t h a t t h e s e a d d i t i o n s p r o x y f o r s o m e o f t h e b a l l

c l a ys .

A s i n o t h e r b r a n c h e s o f t h e c e r a m i c i n d u s t r y , t h e t r e n d is t o w a r d t h e u s e o f

t r e a t e d o r b e n e f lc i a te d c la y s . S o m e o f t h e n e w w h i t e w a r e p r o d u c t s u s e

g r e a t e r p r o p o r t i o n s o f n o n - c l a y m a t e r i a l s s u c h a s s il li m a n i te a n d a l u m i n a .

C l a y s a r e s t i l l n e e d e d , h o w e v e r , t o p r o m o t e p l a s t i c i t y n e c e s s a r y f o r f o r m i n g

a n d t h e m u l l i t e a n d g l a s s y b o n d s n e e d e d f o r f ir e d s t r e n g t h .

T H E R E F R C T O R I E S I N D U S T R Y

T h e r e f r a c t o r i e s i n d u s t r y i n r e c e n t y e a r s h a s u s e d a c o n s i d e r a b le p r o p o r t i o n

o f t h e a n n u a l c l a y p r o d u c t i o n . I n 1 9 44 t h e r e f r a c t o r ie s i n d u s t r y a c c o u n t e d f o r

a b o u t 3 0 p e r c e n t o f t h e c l ay s u s e d

Minerals Yearboo/c,

1944) . W hi l e t h i s

p r o p o r t i o n d e c r e a s e d t o a b o u t 1 0 p e r c e n t i n t h e l a t e 1 9 5 0 s , i t r e p r e s e n t e d

o n l y a s l ig h t d e c r e a s e i n t o t a l t o n n a g e f r o m t h e 1 9 44 f ig u r e s

Minerals

Yearbook,

1957, 1958, 1959) .

T h e n u m b e r o f r e f ra c t o ri e s t h a t a r e b a s e d o n c l a y is lo n g. A n a b b r e v i a t e d

l i s t w o u l d i n c l u d e t h e s e m a j o r p r o d u c t s Modern Refractories Practice,

1 9 50 , p p . 2 0 - 2 2 ) : (1 ) f i r e c la y b r i c k - - a l l c l a ss e s ; (2 ) h i g h a l u m i n a b r i c k - - m o s t

c l a s se s ; (3 ) l a d l e b r i c k a n d a c i d p r o o f b r i c k ; (4 ) a l a r g e v a r i e t y o f m o n o l i t h i c

r e f r a c t o r i e s i n c l u d i n g e a s t a b l e s , p l a s t i c f i r e b r i c k , r a m m i n g a n d g u n n i n g

m i x e s ; (5 ) t r e a t e d c l a y s s o ld f o r s p e c i a l u s e s ; a n d (6 ) r e f r a c t o r y m o r t a r s .

F i r e c l a y b r i c k a re s h a p e d i n a v a r i e t y o f w a y s . M o s t o f t h e m a r e p o w e r

p r e s s e d , m a n y a r e e x t r u d e d , a le s se r n u m b e r a r e s li p c a s t, a n d s o m e o f t h e

s p e ci al s h a p e s a r e h a n d m o l d e d . A l t h o u g h t y p i c a l l y t h e y a r e b u r n e d , a t l e a st

e x p e r i m e n t a l l y , s o m e h i g h c a l c i ne t y p e s h a v e b e e n p l a c e d i n s e r v ic e a s

u n b u r n e d p r o d u c t s . N a t u r a l l y , t h e m o n o l i t h ic p r o d u c t s , w h i c h m a y c o n t a i n

c a lc in e d g r o g c o m p o n e n t s , a re s ol d u n s h a p e d a n d u n b u r n e d . T h e s e m o n o -

l i t h i c l i n i n g s a r e e m p l a c e d d i r e c t l y i n t h e f u r n a c e b y a i r - r a m m i n g , g u n n i n g

o r c a s t i n g a n d a r e t h e n f i r e d i n p l a c e e i t h e r i n t h e f i r s t h e a t - u p o r p r i o r t o

s e r v i c e .

M o s t o f t h e s e r e f r a c to r y p r o d u c t s a r e m a d e f r o m c l ay s t h a t a r e ri c h in

k a o l i n i t e a n d f r o m t h e h i g h - a l u m i n a c l a y s w h i c h c a r r y d i a s p o r e , g i b b s i te ,

b o e h m i t e a n d o t h e r a l u m i n u m h y d r a t e s. T h e y d e p e n d u p o n t h e f o r m a t i o n o f

s il ic e o u s g l a ss e s, m u l l i te , o r c o r u n d u m , o r c o m b i n a t i o n s o f t h e s e , f o r th e i r

c e r a m i c b o n d s .

T h e A m e r i c a n S o c i e t y f o r T e s t i n g M a t e r i a l s r e c o g n i z e s m a n y c l a s s e s o f

f ir e c la y a n d h i g h - a l u m i n a b r ic k , b a s e d g e n e r a l ly o n t h e i r m e l t i n g b e h a v i o r

a n d a l u m i n a c o n t e n t s . T h e c l a s si f ic a t io n o f r a w m a t e r i a l s u s e d i n t h e s e

p r o d u c t s , h o w e v e r , is n o t s o w e l l e s t ab l i sh e d . F o r e x a m p l e , N o r t o n ( 19 49 ,

p . 2 7 ) r e c o g n i z e s a f i re c l a y a s a c l a y h a v i n g a P C E o f 1 9 o r h i g h e r . T h e c e r a m i c

i n d u s t r y h a s u s e d l o o s e c l a s s i f i c a t i o n s f o r f i r e c l a y s w h i c h i n c l u d e t h e f o l l o w -

i ng : ( 1 ) f l i n t a nd s e m i - f l i n t c l a ys , ( 2 ) p l a s t i c a nd s e m i - p l a s t i c c l a ys , ( 3 )

k a o l i n s , a n d (4 ) s il ic e o u s cl a y s . H i g h - a l u m i n a c l a y s , a l s o b r o a d l y c l a s si fi e d a s

f ir e c la y s , i n c l u d e d i a s p o r e c l a y s , b u r l e y c l a y s, a n d o t h e r t y p e s c o m m o n l y

f o u n d a s s o c i a t e d w i t h b a u x i t e s . F i r e e l a y s a r e a ls o lo o s e l y d e f in e d a s n o n -

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313

w h i t e - b u r n i n g c l ay s . T i le t e r m f i re c l ay i n c o m m o n u sa g e h a s s o m a n y

c o n n o t a t i o n s t h a t i t i s a l m o s t m e a n i n g l e s s .

T h e r e fr a c to r i n e ss o f l ad l e b ri c k w h i c h c a n n o t b e c o m p a r e d t o p r o d u c t s

m a d e f r o m p u r e k a o l i n i te d e p e n d s f o r t h e d e s ir e d p r o p e r t i e s u p o n a

s iz e a bl e p r o p o r t io n o f t h r e e -l a y e r c l ay m i n e r a ls t h a t e x p a n d u p o n h e a t i n g .

T h u s i t c a n b e s e e n f r o m t h e s e v a r i o u s c l a s si fi c at io n s o f c la y s u s e d i n

r e fr a c to r ie s t h a t a v a r i e t y o f m i n e r a l a s s e m b l a g e s o r m i x t u r e s a r e u s ed . T h e

r e q u i re m e n t s h o w e v e r a r e s u c h t h a t t h e m a j o r c l a y m i n e r a l is k a o l i n it e i n

a s so c i at io n w i t h a l u m i n u m h y d r a t e s a n d q u a r t z . I n r e l a t io n t o o t h e r i n d u s t r ie s

u s i n g c la y s t h e c l a y s u s e d i n r e f r a c to r i e s m u s t b e r e l a t i v e l y f r e e f r o m a l k a l i e s

a n d f r o m c o m p o u n d s o f i ro n t i t a n i u m o r a l k a li n e e a r th s .

I n a d d i t io n t o t h e r e f r a c t o r y p r o d u c t s t h a t c o n t a in c la y s a s t h e i r m a j o r

r a w m a t e r ia l s n u m e r o u s o t h e r r e f r a c t o r y p r o d u c t s i n c o r p o r a t e c l a y s a s

m i n o r o r t r a c e c o n s t it u e n t s. T h e s e i nc l ud e s o m e v e r y h i g h - a ] u m i n a p r o d u c t s

m a n y b a si c r e f ra c t o r ie s b a s e d o n c h r o m e o r e a n d m a g n e s i a a n d a n u m b e r o f

s p e c ia l r e f r a ct o r i es . A l t h o u g h r e f r a c t o r y c l ay s a r e e m p l o y e d in m a n y o f t h e s e

a p p l i c a ti o n s t h e c l a y s a r e b e i n g u s e d f o r o n e o r m o r e s p e c ia l r e a s o n s . C l a y s

o f h i g h p u r i t y a n d s p e c i a l l y g r o u n d o r o t h e r w i s e t r e a t e d c l a y s a r e o f t e n u s e d

t o in c r e a s e p l a s t i c i ty a s p r e s si n g a i d s t o i n c re a s e g r e e n a n d d r i e d s t r e n g t h o r

t o p r o m o t e f ir ed b o n d s .

C l a y s o f h i g h p u r i t y a n d s p e c i a ll y t r e a t e d k a o l i n s a r e u s e d in s o m e o f t h e s e

a p p l i c a t i o n s . B a l i c l a y s a n d b e n t o n i t e s m a y b e e m p l o y e d . T h e r e a s o n f o r

u s i n g t h e s e c l a y s a s p l a s t ic i z e r s a n d p r e s s in g a i d s a r e o b v i o u s . T h e c l a y s a r e

a l so u s e d a s c o m p o n e n t s t o a i d d i s p e r s io n in s li p s t h a t a r e n o t b a s i c a l l y c l a y

s li ps . T h e i r u s e s a s h i g h - t e m p e r a t u r e b o n d s h o w e v e r a r e n o t q u i t e s o

o b v i o u s .

I n h i g h - a l u m i n a m i x e s w h e r e c o r u n d u m a n d m u l l i t e a r e t h e n o r m a l f i r e d

p h a s e s c l a y s u s e d a s b o n d i n g a g e n t s m a y y i e l d c r i s to b a l i t e a n d g l a ss i n

a d d i t io n t o m u l li te . T h e m u l l it e s u p p li e d b y t h e f ir ed c l ay m a y b e i m p o r t a n t

i n t h a t i t s i n t e r g r a n u l a r p o s i t i o n c a n p r o m o t e a f i r m e r b o n d . I n b a s i c r e f r a c -

t o ri es c l ay s m a y b e u s e d t o f o r m m a g n e s i u m a l u m i n a t e s p in e ls f o r st e ri te

o r o t h e r s i l i c a t e s a s f i r e d b o n d s .

R e c e n t l y t h e r e h a s b e e n a t r e n d t o w a r d g r e a t e r u s e o f m o n o l i t h i c r e f ra c -

t o r y l in i n g s. M o n o l i th i c r e f r a c to r i e s s in c e t h e y a r e i n e s se n c e f o r m e d d u r i n g

i n s t a ll a t io n m a y r e q u i r e a h ig h e r d e g r e e o f p l a s t i c i t y o r g r e a t e r u n f i re d

s t r e n g t h t h a n t h e i r c o m p a r a b l e f ir e d c o u n t e r p a r t s . T h e s e d if f e re n t r e q u i r e -

m e n t s a r e o f t e n s a t is f a c to r i ly m e t b y t h e a d d i t i o n o f s m a l l a m o u n t s o f cl a y s

s o m e o f w h i c h w o u l d n o t m e e t t h e p r e s e n t d e f in i ti o n o f r e f ra c t o r y c l a y . A

h y p o t h e t i c a l e x a m p l e m i g h t b e t h e u s e o f a c l a y o f l o w r e fr a c to r i n e ss b u t

h i g h p l a s t i c i ty i n a g u n n i n g c a s ta b l e to p e r m i t s a t i s f a c t o r y e m p l a c e m e n t in

a s h o r t p er i o d o f t i m e w i t h a m i n i m u m o f w a s t e. M a n y m o r e e x a m p l e s c o u ld

b e c it e d b u t i t is h o p e d t h a t t h o s e m e n t i o n e d h e r e i n d i c a t e t h e c o n s i d e r a b le

v a r i e t y o f t h e u s es o f c la y s in t h e r e f r a c to r i e s i n d u s t r y a n d t h e i r i m p o r t a n c e

t o t h e i n d u s t r y .

A b r i e f l o o k a t s o m e r e c e n t s t a t is t i c s o n t h e p r o d u c t i o n a n d s a le is i n

o r d e r . T h e s e s t at i st i c s w h e n r e l a t e d t o t h o s e a m o u n t s u s e d in t h e c e r a m i c

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314 T E N T H N A T I O N A L C ON I~E RE BT CE O:N C L A Y S A N D C L A Y

MINER LS

industries, tend to show the influence of some of the recent trends on the

clay market and, further, give some basis for a look into the future importance

of clays in ceramics. It should be noted, however, that the statistics reported

for the 1940 s and early 50 s ma y n ot have been as comprehensive as those

that have been published more recently.

R E C E N T T R E N D S O F C L A Y U S E I N T H E C E R A M I C

I N D U S T R I E S

I n t h e p a s t d e c a d e t h e a m o u n t o f c l a y s p r o d u c e d a n d s o l d i n t h e U n i t e d

States has shown an increase. The dual classification of produ ed and sold is

necessary, for in many cases, tremendous tonnages of clays are produced

5

O

o ~ o

co

o

20

. J

IO

R

P = O D U C ~ ] ~ , A ~ O L D

CLAY USED BY

CERAMIC INDUSTRIES I i

-~:

~ 1 I ~ / ~

9 ~ : \ ~

9

~ - ~

1 9 4 4 1 9 5 0 19 51 1 9 5 2 1 9 5 ~ 1 9 5 4 1 9 5 5

/

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s

. 1

1 9 5 6

t i

1 t l I

/ / :

l i

1 9 5 7 1 9 5 8

FIGURE 1.---Total clays produced and sold, used by the ceramics industries and by the

refractories industry; 1944 through 1958.

which are sold only as finished products. In other cases, crude clays are sold

as the finished product.

Figure 1 shows the relationships between annual clay production and the

amount of clays used by the ceramics industries as well as the portion used

by the refractories industry for the years 1944 and 1950 through 1958. The

1944 production figures were chosen because (1) they are representative of

the early 40 s and (2) 1944 was the first year in which the data included total

amounts of clays used by industry. It was unfortunate that the early 1940

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C L A Y M I N E R A L S I N T H E C E R A M I C IN D U S T R I E S

315

figures were not broken down so that the data for the ceramic industries

could be analyzed. There was, in tha t period, a tremendous mid-war pea k of

use by the refractories industry at th e same time as a fractional structural clay

production. Table 1 has been compiled to show the average tonnages for the

years 1944, 1945 and 1946. This table shows the total clays used by industry,

the totals used in ceramics and the proportion of the total used in ceramics in

general and refractories in particula r for the middle 1940 s and 1950 thr oug h

1958.

Table 1 and Fig. 1 show a tremendous jump in total production from the

middle 40 s to the 50 s. This jump in tot al is also reflected in the jump in

tonnage of clay used b y the ceramics industries. It is also evident, however,

tha t the a moun t of clay used annually by the refractories industr y was abou t

the same in the 40 s as it was in the 50 s. This reflects improved efficiency in

the use of refractories.

70

:L 65 PER CENT OF TOTAL USED IN ALL CERAMIC INDUSTRIES

o 2

t

1944 195 1951 1952 1953 I9 54 1955 1956 1957 1958

FIG~JRE 2.--Proportion of clays produced and marketed, used by all ceramic industries

and the refractories industry; 1944 and 1950 through 1958.

Figure 2 shows the proportion of the annual clay production used b y the

ceramic industries as a whole and the refractories industry in particular for

the same years. The considerable decrease in percentage of total clays used

by the refractories industry while the tonnages remain about the same gives

an idea of the general growth of the ceramics industries.

As have all other industries that use clay, the ceramic industries have gone

to the use of greate r proportions of the more highly refined and specially

trea ted clays. Along with this trend, there has been a clearly discernable

increase in the dollar value per unit of clay. This not only reflects added

production cost but also added quality. Murray (this Volume) has given some

idea of the tremendous differences in kaolins marketed . Many of the clays

available for use now bear little resemblance to their parent materials.

In the refractories industries, the trend is toward specialization, with a

specific refractory designed for a single and very particular application.

Missile launching pads, for instance, must be able to withstand conditions

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3 6 T E N ~ N A TIO N AL C O N F ] ~ E N C E ON C L A Y S A N D C L AY M I NE R AL S

9

9

co

~o

o ~ ~ o

~

~o

~

o

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~ L A Y M I I ~ E R L S IN T H E C E R M I G I N D U S T R I E S

3 1 7

t h a t f o r m e r l y d i d n o t e x i s t . I n o t h e r f i e l ds , r e f r a c t o r y c o a t i n g s h a v e b e e n

c a l l e d f o r t o p r o t e c t m e t a l p a r t s w h i c h f o r m e r l y w o u l d h a v e b e e n c a p a b l e o f

w i t h s t a n d i n g t h e s e r v i c e c o n d i t io n s . I n a n o t h e r i n s t a n c e , a s m a l l s p e c i a l t y

g l as s p r o d u c e r m i g h t w a n t a s p e c ia l ly m a d e m e l t i n g p o t . M a n y o f t h e s e

s p e c i a l i t e m s , o f c o u r se , a r e d e v e l o p e d f i o m r e f r a c t o r y c l a y b a s e d m a t e r i a l s ;

o t h e rs m u s t r e l y o n o t h e r r e f r a c t o r y m a t e r i a l s s u ch a s b a s i c o r h ig h p u r i t y

o x i d e c e r am i c s . O t h e r b r a n c h e s o f t h e i n d u s t r y c o n t i n u e t o u s e l a r g e t o n n a g e s

o f c la y e a c h y e a r w i t h n e w c l a y p r o d u c t s b e i n g d e v e l o p e d t o o f fs et d is c o n -

t i n u e d u s e o f o u t m o d e d p r o d u c t s .

I n s u m m a r y , i t n o w a p p e a r s t h a t t h e c e r a m i c in d u s t r i e s w i l l c o n t in u e t o

u s e t h e l a r g e s t p r o p o r t i o n o f t h e a n n u a l c l a y p r o d u c t i o n . A l t h o u g h t h a t

p r o p o r t i o n m a y n o t g r e a t l y c h a n g e , i t w i l l r e p r e s e n t a n i n c re a s e o f t o t a l c l a y

p r o d u c t i o n a n d n o t a d i s e e r n a b l e d e c r e a s e i n t h e u s e o f c la y s i n c e r a m i c s .

R E F E R E N C E S

M c N a m a r a , E . P . ( 1 9 4 9 ) C e r a m i cs v . 3 C l a y P r o d u c t s a n d W h i t e w a r e s : P e n n s y l v a n i a

Sta te Col lege , S ta te Col lege , Pennsy lvan ia .

M i n e r a l s Y e a r b o o k (19 44 ) U .S . B u re a u o f Mine s, D iv i s io n o f Min e ra l s, U .S . G o v t .

Pr in t ing Off ice .

M i n e r a l s Y e a r b o o l z (1950-1958) U.S . B ure au o f Mines, Div is ion o f Minera ls , U.S . G ovt .

Prinbing Office .

M o d e r n R e f r a c t o r y P r a c t i c e (1 95 0) 3 r d e d . , H a r b i s o n - W a l k e r R e f r a c to r i e s C o m p a n y ,

P i t t s b u r g h , P e n n s y l v a n i a , 43 9 p p .

M u r ra y , 1 4. H . (19 6 2) In d u s t r i a l a p p l i c a t io n s o f k a o l in : T h i s v o lu me .

Norton, F. 14. (1949) R e f r a c t o r i e s : 3 rd e d . , M c Gra w -Hi l l , Ne w Y o rk , 7 82 p p .

Po luek tov a , E . F . (1960) U.S .S .R . Pa t en t No . 86 , pp . 111-116 , a lso , C h e m . A b s t r a c t s :

v. 55, no. 14, col . 13779 c , 10 Ju ly 1961.