Refractory metallization of green ceramic
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processing characteristics: 1) In p o s t f i r e d m e t a l l i z a t i o n , the s i n t e r i n g p r o c e s s is optimized for a d h e s i o n s t r e n g t h of the m e t a l l i zation; w h e r e a s , 2) In c o f i r e d m e t a l l i z a t i o n , the s i n t e r i n g p r o c e s s is optimized for c e r a m i c d e n s i f i c a t i o n . A c o f i r e d m e t a l l i z a t i o n may have oxidizable m e t a l additives c o m p l e t e l y l e a c h e d from it into the c e r a m i c and, thus, fail to p e r f o r m its objective at the i n t e r face. The s a m e i s t r u e for other g l a s s additives which r e a c t r e a d i l y with the c e r a m i c . C o n v e r s e l y , if the g l a s s y phase in the c e r a m i c wets well to the m e t a l , then the g l a s s m a y be leached f r o m the c e r a m i c into the m e t a l l i z a t i o n t h e r e b y coating the m e t a l p a r t i c l e s . This i s u n d e s i r a b l e since p r o b l e m s in plating a n d b r a z i n g to the m e t a l l i z a t i o n would occur. The e x p e r i m e n t a t i o n to d e t e r m i n e a p p r o p r i a t e m e t a l lizing on " g r e e n " a l u m i n a was d i r e c t e d t o w a r d the use of pure m e t a l s without oxidizable c o m p o n e n t s . Also, b e c a u s e m a n y c e r a m i c types a r e to be m e t a l lized, it i s i m p o r t a n t that the p r o c e s s be e a s i l y t r a n s f e r a b l e from one c e r a m i c s y s t e m to the next. F o r a given c e r a m i c to be m e t a l l i z e d , the c o m p o s i t i o n and s i n t e r i n g range is fixed; thus, the m e t a l l i z a t i o n should be designed to cofire with the c e r a m i c . In the design of the m e t a l l i z a t i o n to fit d i f f e r e n t c e r a m i c types, chemical bonding as a comprehensive approach a p p e a r s difficult. T h u s , specific effort was d i r e c t e d toward a m e c h a n i c a l bond and s e v e r a l a s s u m p t i o n s were m a d e : 1) S t r e s s e s at the i n t e r f a c e of the c e r a m i c and m e t a l m u s t be m i n i m i z e d . 2) I n t e r f a c e s t r e s s e s a r e m i n i m i z e d by m a t c h i n g the s h r i n k a g e of the c e r a m i c with that of the metal. 3) Shrinkage of the m e t a l l i z a t i o n may be c o n t r o l l e d at a given s i n t e r i n g condition by v a r y i n g the p a r ticle size of the m e t a l . 4) M e c h a n i c a l i n t e r l o c k i n g of the m e t a l in the cer a m i c s u r f a c e i s a n e c e s s a r y condition for good bond. 5) Matching s h r i n k a g e s of c e r a m i c and m e t a l l i z a t i o n would allow c o n t r o l of c a m b e r , a d e s i r a b l e feat u r e in m e t a l - c e r a m i c c o m p o s i t e s . This r e p o r t i n v e s t i g a t e d in detail the s y s t e m of c o m m e r c i a l l y pure a l u m i n a * and t u n g s t e n m e t a l l i z a t i o n . *AlcoaA-16 alumina. VOLUME 1, MARCH 1970-685
S t u d i e s c o n d u c t e d on o t h e r c e r a m i c s and p u r e e l e
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