Dilatometry of pitch-anthracite mixes for carbon
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PITCH
a n t h r a c i t e m i x e s a r e u s e d to m a k e m o n o l i t h i c linings f o r e l e c t r o l y t i c c e l l s u s e d in a l u m i n u m p r o duction. D i l a t o m e t r y of t h e s e m i x e s is i m p o r t a n t in u n d e r s t a n d i n g the o r i g i n of c r a c k s f o r m e d when t h e s e m i x e s a r e b a k e d b e c a u s e c r a c k s can l e a d to p r e m a t u r e f a i l u r e of the c e l l l i n t n g s . l A c o n s i d e r a b l e l i t e r a t u r e e x i s t s on the b a k i n g d i l a t o m e t r y of c o a l s 2 and b r i q u e t t e d c o a l s . 3 However, v e r y l i t t l e h a s b e e n w r i t t e n about p i t c h m i x e s c o n t a i n i n g carbon aggregates. For coke-pitch mixtures prebaked to 500~ Bowitz and S a n d b e r g 4 found s l i g h t e x p a n s i o n followed b y s h r i n k a g e b e t w e e n 500 and 1000~ Nakam u r a and A t l a s s s t u d i e d d i f f e r e n t i a l t h e r m a l a n a l y s i s and d i l a t o m e t r y of b i n d e r - c o k e m i x t u r e s h e a t e d f r o m r o o m t e m p e r a t u r e . F o r m i x t u r e s containing p i t c h b i n d e r s , they r e l a t e d m a x i m u m c o n t r a c t i o n to p e r i o d s of g r e a t e s t d e v o l a t l l i z a t i o n . F o r r e s i n b i n d e r s , the r e l a t i o n to DTA was m o r e c o m p l e x . A r e c e n t r e p o r t d e s c r i b e s in g r e a t e r d e t a i l the d i l a t o m e t r y of r e s i n - c o k e mlxes.6 R e s u l t s a r e r e p o r t e d h e r e of an i n v e s t i g a t i o n of the d t l a t o m e t r y of p i t c h - a n t h r a c i t e m i x e s a s they a r e heated from room temperature.
of the o u t e r tube. Beneath the s a m p l e tube, but not in c o n t a c t with it, was a c a r b o n r o d r e s t i n g on a r i n g n e a r the top of the s u p p o r t tube. A t h e r m o c o u p l e e x tended to within 6 m m of the top s u r f a c e of the c a r b o n r o d . The t h e r m o c o u p l e was c o n n e c t e d to a p r o g r a m c o n t r o l l e r that r e g u l a t e d the h e a t i n g r a t e of the f u r n a c e . M o v e m e n t of the top of the s a m p l e was t r a n s m i t t e d b y an 8 m m q u a r t z e x t e n s i o n r o d , 430 m m long, with a 29 m m d i a m foot r e s t i n g on the s a m p l e . The upper end of the e x t e n s i o n r o d p u s h e d a g a i n s t a d i a l
Table I. Aggregate Sizings
Anthracite Tyler Screen Size +4 -4+8 -8+14 -14+28 -28+48 -48+100 -100+200 -200
A
B
C
D
17.6 21.4 25.3 12.1 9.5 6.5 7.6
25.5 13.6 15.4 10.3 10.9 8.8 4.4 11.1
34.0 10.4 11.3 4.8 4.5 5.1 7.1 22.8
12.2 10.7 13.9 17.8 15.7 12.0 8.4 9.3
MATERIALS In the p r e l i m i n a r y t e s t s , the g r e e n m i x c o n s i s t e d of an a n t h r a c i t e a g g r e g a t e c a l c i n e d at l l 0 0 ~ with 12 p c t b i n d e r m a d e of 1 95 weight r a t i o b l e n d of c o k e - o v e n p i t c h e s having s o f t e n i n g p o i n t s of 110 and 40~ c u b e i n - a i r - o r - w a t e r ( C o m p
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