X-RAY DATA FOR NEW Y-SI-AL-O-N GLASS-CERAMICS

Since the 1970s an increasing number of crystalline oxynitrides have b een observed as gr ain boundary phases in sialon ceramics. In particul ar, the well-known four- and five-component phases in the Y-Si-Al-O-N system have been accepted as the total picture in this system and the potential for new phases has not been considered. However, with furthe r development of sialon glasses and glass ceramics, post-preparative h eat-treatment has revealed a number of previously uncharacterised crys talline phases occurring particularly at temperatures below 1200 degre es C. Three such phases are discussed, I-w, Q and D, all of which have been observed previously by other researchers but without X-ray diffr action data, Q-phase occurs in some rare earth as well as yttrium sial on systems. All these phases can be produced only within a limited tem perature range and are critically dependent on starting como position and heat-treatment temperature, so the present data will complement th ose already existing for devitrified sialon glass products, with poten tially more phases yet to be identified. (C) 1997 Elsevier Science Lim ited.