Petroleum-Derived Carbons - ACS Publications - American Chemical

24 Downloaded by UNIV OF CALIFORNIA SAN DIEGO on September 2, 2015 | http://pubs.acs.org Publication Date: April 14, 1986 | doi: 10.1021/bk-1986-0303.ch024

Carbon-Fiber-Reinforced Carbon Composites Fabricated by Liquid Impregnation Erich Fitzer and Antonios Gkogkidis Institut für Chemische Technik, Universität Karlsruhe, D-7500 Karlsruhe, Federal Republic of Germany

Although developed i n i t i a l l y for aerospace applica tions, carbon/carbon composites are now finding wider uses, e.g., in nuclear reactors, automobiles, metal– forming, and biomedical implants. This paper is con cerned with problems and choices in fabrication, including chemical vapor deposition, but focussing principally on liquid impregnation methods. High final heat treatment temperatures for the carbon fiber are desirable to realize good translation of fiber strength into the composite. "Soft" matrix precursors, e.g., coal-tar pitch, contribute to the composite modulus by alignment of the graphitic layers parallel to the fibers. Stress cycling can destroy the matrix by internal fracturing to fine dust, but this loss of matrix can be limited by a final resin impregnation to produce a hybrid matrix. The hybrid matrix composites have mechanical properties similar to those of polymer– matrix composites, but with reduced flammability. C a r b o n / c a r b o n composites f a b r i c a t e d by m u l t i p l e c y c l e s o f l i q u i d i m p r e g n a t i o n and r e c a r b o n i z a t i o n a r e a t y p i c a l example of modern petroleum d e r i v e d c a r b o n s . I n t h e 1975 ACS Symposium on P e t r o l e u m D e r i v e d Carbons ( 1 ) , papers were p r e s e n t e d on c a r b o n / c a r b o n com p o s i t e m a t e r i a l s formed by p y r o l y t i c i n f i l t r a t i o n p r o c e s s e s ( 2 ) o r by l i q u i d i m p r e g n a t i o n w i t h p e t r o l e u m p i t c h ( 3 , 4 ) , on f a b r i c a t i o n p r o c e s s e s f o r h i g h - m o d u l u s c a r b o n f i b e r s based on p o l y a c r y l o n i t r i l e (PAN) o r p i t c h p r e c u r s o r s (_5), and on t h e use o f c a r b o n m a t e r i a l s f o r t h e r m o s t r u c t u r a l (6_) as w e l l as b i o m e d i c a l a p p l i c a t i o n s (_7_). The p r e s e n t paper addresses t h e problems posed i n these e a r l i e r c o n t r i b u t i o n s from a new v i e w p o i n t , namely t h e development of a s u p e r i o r carbon m a t e r i a l t h a t r e a l i z e s more f u l l y t h e s t r e n g t h , s t i f f n e s s , and t h e r m a l p r o p e r t i e s i n h e r e n t i n t h e s t r o n g c h e m i c a l bonds o f carbon i n t h e g r a p h i t i c l a y e r ( 8 ) . Petroleum p r o d u c t s , as t h e c a r b o n p r e c u r s o r s f o r p i t c h - b a s e d carbon f i b e r s and f o r t h e carbon m a t r i x o f t h e c o m p o s i t e , have proved a d v a n t a geous f o r such s u p e r i o r carbon m a t e r i a l s . 0097-6156/86/0303-0346$09.50/0 © 1986 American Chemical Society

In Petroleum-Derived Carbons; Bacha, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

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Carbon Composites

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Downloaded by UNIV OF CALIFORNIA SAN DIEGO on September 2, 2015 | http://pubs.acs.org Publication Date: April 14, 1986 | doi: 10.1021/bk-1986-0303.ch024

A p p l i c a t i o n s o f Carbon/Carbon Composites The performance o f c a r b o n / c a r b o n composites became w e l l known t o the g e n e r a l p u b l i c by t h e r e p e a t e d s u c c e s s f u l l a n d i n g s o f t h e American space s h u t t l e s , i n w h i c h 2D c a r b o n / c a r b o n composites, r e i n f o r c e d t w o - d i m e n s i o n a l l y by a f i b e r web o r f a b r i c , a r e used f o r s t r u c t u r a l p a r t s t h a t a r e c r i t i c a l d u r i n g r e e n t r y , such a s t h e nose cap and t h e l e a d i n g edges o f t h e w i n g s ; s e e F i g u r e 1 (9) · Because o f i t s h i g h s t r e n g t h and i n f u s i b i l i t y even a t v e r y h i g h t e m p e r a t u r e s , as w e l l as i t s l o w d e n s i t y , carbon-fiberr e i n f o r c e d carbon i s most s u i t a b l e as d i s c b r a k e m a t e r i a l f o r s u p e r s o n i c a i r c r a f t such as t h e c i v i l i a n CONCORDE and n e a r l y a l l military jets; see F i g u r e 2. For this a p p l i c a t i o n , 2D carbon/carbon composites are preferred. The performance c h a r a c t e r i s t i c s o f d i s c m a t e r i a l s as t e s t e d by SEP F r a n c e a r e compared i n F i g u r e 3 (SEPCARB i s ^ t h e t r a d e name f o r c a r b o n / c a r b o n composites f a b r i c a t e d by S o c i é t é Europeene de P r o p u l s i o n ) . The high tolerable concentration of consumed energy i n the c a r b o n / c a r b o n brake d i s c s s h o u l d be noted ( 1 0 ) . In t h e near f u t u r e , i t i s planned t o r e p l a c e t h e c o n v e n t i o n a l a s b e s t o s b r a k e l i n i n g s f o r automobiles by m o d i f i e d c a r b o n / c a r b o n composites ( 1 1 , 1 2 ) . C a r b o n / c a r b o n m a t e r i a l s a r e c u r r e n t l y used i n t h e most c r i t i c a l parts of s o l i d - f u e l rocket engines. A test nozzle f o r the F r e n c h ARIANE r o c k e t i s shown i n c r o s s s e c t i o n a f t e r f i r i n g i n F i g u r e 4 t o demonstrate t h e undamaged s u r f a c e o f t h e 3D composite w i t h i n the throat of the nozzle (10). Carbon/carbon composites are also used as refractory components i n g a s - c o o l e d h i g h - t e m p e r a t u r e n u c l e a r r e a c t o r s , e . g . , i n t h e heat exchanger between t h e p r i m a r y and secondary h e l i u m cooling c i r c u i t s (13). Gas t u r b i n e s have been b u i l t w i t h b l a d e s made from c e r a m i c m a t e r i a l s and u s i n g l D - r e i n f o r c e d c a r b o n - c a r b o n c i r c u m f e r e n t i a l rings developed by DFVLR, S t u t t g a r t ( 1 4 ) (DFVLR = Deutsche F o r s c h u n g s - und V e r s u c h s a n s t a l t f u r L u f t und R a u m f a h r t ) ; s e e Figure 5. In t h i s a p p l i c a t i o n the carbon-carbon r i n g provides compressive p r e s t r e s s on t h e ceramic t u r b i n e b l a d e s , w h i c h a r e sensitive to tensile stress. A r e c e n t s u c c e s s f u l a p p l i c a t i o n o f c a r b o n / c a r b o n composites i s the t o o l f o r s u p e r p l a s t i c f o r g i n g o f t i t a n i u m i l l u s t r a t e d by F i g u r e 6; tubes up t o 1.5 m i n l e n g t h c a n be f o r g e d a t t e m p e r a t u r e s up t o 1000°C, thus o f f e r i n g a r a p i d a l t e r n a t i v e f a b r i c a t i o n t e c h n i q u e t o p r e s e n t p r o d u c t i o n methods, e . g . , r i v e t e d tubes ( 1 5 ) . Contact brushes f o r e l e c t r i c a l commutators, made w i t h c a r b o n f i b e r s and c a r b o n / c a r b o n composites ( 1 6 ) , a r e opening a n o t h e r new f i e l d o f application. F u r t h e r m o r e , p i s t o n s i n d i e s e l e n g i n e s have been proposed t o be made from c a r b o n / c a r b o n composites ( 1 7 ) . F i n a l l y t h e use of c a r b o n - f i b e r - r e i n f o r c e d carbon m a t e r i a l s f o r i m p l a n t a t i o n purposes i n human m e d i c i n e s h o u l d be m e n t i o n e d . One o f t h e most i m p r e s s i v e a p p l i c a t i o n s i s t h a t f o r h i p j o i n t s . I n F i g u r e 7 a s t a t e - o f - t h e - a r t h i p j o i n t made from a c o b a l t a l l o y w i t h a p o l y e t h y l e n e s o c k e t i s compared w i t h a d e s i g n concept employing a carbon-fiber-reinforced carbon stem i n a p o l y g r a n u l a r carbon socket. Such a stem d e s i g n o f f e r s t h e p o s s i b i l i t y t o approach c l o s e l y t h e femur s t r u c t u r e by a p p r o p r i a t e c o m b i n a t i o n o f 1 D - , 2D,

A m c a e r n i C h e m c a i lS o c e i t y L b i r a r y 1155 16th St., N.W.

In Petroleum-Derived Carbons; Bacha, J., et al.; Washington, 20036 ACS Symposium Series; American ChemicalO.C. Society: Washington, DC, 1986.

PETROLEUM-DERIVED CARBONS


348

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F i g u r e 1. The l e a d i n g edge ( L . E . ) of the wing, and the nose cap of the COLUMBIA space s h u t t l e (9_) a r e made of r e i n f o r c e d c a r b o n composites (RCC).

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F i g u r e 3. Comparative performance a i r c r a f t brakes ( 1 0 ) .

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F i g u r e 5. A t u r b i n e r o t o r made w i t h ceramic b l a d e s and a c a r b o n - c a r b o n composite r i n g t o w i t h s t a n d t e n s i l e s t r e s s e s (14) •




Carbon Composites


24.

F i g u r e 6. Above: a tool for the s u p e r p l a s t i c forging of t i t a n i u m , made e n t i r e l y from c a r b o n / c a r b o n composites (15). Below: a i r c r a f t exhaust m a n i f o l d formed from t i t a n i u m by s u p e r p l a s t i c forging with the carbon/carbon t o o l .


351


352


Reinforced Carbon Composite 1- D R E I N F O R C E M E N T (NECK: HIGHEST FLEXURAL STRESS) 2- D R E I N F O R C E M E N T (TRANSVERSEand LONGITUDINAL STRENGTH) 3- D R E I N F O R C E M E N T (INTRAMEDULLARY SCREW THREAD/ILSS) 1-D R E I N F O R C E M E N T (STEM: HIGH FLEXURAL STRENGTH)

F i g u r e 7. Comparison o f a c o n v e n t i o n a l h i p j o i n t fabricated from c o b a l t a l l o y s w i t h a j o i n t d e s i g n u s i n g carbon-fiberr e i n f o r c e d composites t a i l o r e d t o meet s p e c i f i c l o c a l s t r e s s requirements ( 1 8 ) .


24.



Carbon Composites

353

and 3 D - r e i n f o r c e d c o m p o s i t e s ( 1 8 , 1 9 ) . Some v a l u e s of f l e x u r a l s t r e n g t h and Young's modulus achievable by v a r i o u s types of c a r b o n / c a r b o n c o m p o s i t e s a r e shown i n F i g u r e 8 ( 2 0 ) . A wide range of s t r e n g t h and s t i f f n e s s i n v a r i o u s d i r e c t i o n s can be d e s i g n e d i n t o such t a i l o r e d m a t e r i a l s . The p r o p e r t i e s of t h e Co-Cr-Mo alloys t h a t a r e used f o r m e d i c a l i m p l a n t s a r e compared with m e c h a n i c a l d a t a f o r human bones t o demonstrate t h a t c a r b o n / c a r b o n composites a r e p r o m i s i n g c a n d i d a t e s f o r i m p l a n t a t i o n i n t h e f u t u r e .


F a b r i c a t i o n Processes

f o r C a r b o n / C a r b o n Composites

P r o c e s s e s f o r f a b r i c a t i o n o f c a r b o n / c a r b o n c o m p o s i t e s by " g a s - p h a s e i m p r e g n a t i o n " and by " l i q u i d - p h a s e i m p r e g n a t i o n " were d e s c r i b e d i n t h e 1975 Symposium ÇL). The vapor i m p r e g n a t i o n p r o c e s s was f i r s t used f o r f a b r i c a t i o n of the s p e c i a l a i r c r a f t b r a k e s r e q u i r e d f o r the commercial j e t CONCORDE, and i s s t i l l i n u s e , a l t h o u g h most new c a r b o n / c a r b o n p a r t s and even a i r c r a f t b r a k e s a r e now produced by t h e more e c o n o m i c a l p i t c h - i m p r e g n a t i o n p r o c e s s e s . The g a s - p h a s e impregnation process (in-pore deposition of p y r o l y t i c carbon) i s d i f f i c u l t t o p e r f o r m because of the tendency f o r pore c l o s i n g i n s t e a d of pore f i l l i n g . F i g u r e 9 shows t h e r e s u l t s of c h e m i c a l vapor i m p r e g n a t i o n (CYI) e x p e r i m e n t s w i t h S i C d e p o s i t i o n i n t u b e - l i k e model pores i n a p o l y g r a n u l a r g r a p h i t e body. SiC d e p o s i t i o n was used f o r b e t t e r r e c o g n i z a b i l i t y of the CV deposits. The tendency t o d e p o s i t i n the pore e n t r a n c e s can readily be u n d e r s t o o d if the o v e r a l l d e p o s i t i o n r a t e of the heterogeneous r e a c t i o n i s c o n t r o l l e d by the c h e m i c a l d e p o s i t i o n r a t e and n o t by t r a n s p o r t phenomena ( 2 1 ) . Transport c o n t r o l occurs mainly at the h i g h e r d e p o s i t i o n temperatures. I n F i g u r e 10 ( l e f t - h a n d s i d e ) e x p e r i m e n t a l r e s u l t s on p e n e t r a t i o n d e p t h i n p o l y c r y s t a l l i n e g r a p h i t e a r e shown by dashed l i n e s as a f u n c t i o n of d e p o s i t i o n t e m p e r a t u r e . The d e c r e a s e i n p e n e t r a t i o n depth can be p r e c a l c u l a t e d f o r v a r i o u s pore d i a m e t e r s i f t h e d i f f u s i o n b e h a v i o r of the gaseous s p e c i e s and t h e r a t e of the c h e m i c a l d e p o s i t i o n r e a c t i o n a r e known. For t h i s c a l c u l a t i o n t h e d i m e n s i o n l e s s Damkohler I I number ( i d e n t i c a l w i t h the square of t h e T h i e l e modulus) can be used as i n d i c a t e d i n t h e r i g h t - h a n d s i d e of F i g u r e 10. The r e s u l t s of p r e c a l c u l a t i o n a r e shown i n t h e l e f t - h a n d s i d e and i n d i c a t e t h a t the e x p e r i m e n t a l d a t a f i t t h e p r e c a l c u l a t e d d a t a q u i t e w e l l i f the d e c r e a s e s i n pore d i a m e t e r d u r i n g CVI a r e t a k e n into consideration (22-25). P o r e f i l l i n g w i t h o u t pore b l o c k i n g can more e a s i l y be a c h i e v e d by l i q u i d i m p r e g n a t i o n ; see F i g u r e 11 ( 2 6 ) . F u r t h e r m o r e , pore f i l l i n g can be improved by i m p r e g n a t i o n and c a r b o n i z a t i o n a t h i g h pressure. In r e c e n t y e a r s , we have performed s e v e r a l b a s i c s t u d i e s ( 2 7 - 2 9 ) of the l i q u i d i m p r e g n a t i o n p r o c e s s . The l i q u i d i m p r e g n a t i o n p r o c e s s f o r c a r b o n / c a r b o n c o m p o s i t e s i s s i m i l a r t o the i n d u s t r i a l f a b r i c a t i o n p r o c e s s f o r t h e h i g h density graphite electrodes required for ultra-high-power steel furnaces. F i g u r e s 12 and 13 show the a n a l o g i e s as w e l l as the differences between the two p r o c e s s e s . In b o t h cases, the heterogeneous s t r u c t u r e c o n s i s t s of two c o n s t i t u e n t s : (a) p r i m a r y c a r b o n , w h i c h i s i n t r o d u c e d as e l e m e n t a l c a r b o n d u r i n g t h e p r o c e s s s t e p of " g r e e n f a b r i c a t i o n , " and (b) secondary c a r b o n , formed by t h e r m a l d e g r a d a t i o n of t h e carbonaceous b i n d e r d u r i n g t h e p r o c e s s


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Petroleum-Derived Carbons - ACS Publications - American Chemical

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