Optimisation of Heat Treatments for Oxynitride Glass-Ceramics

Nucleation and crystallisation of a Y-Si-Al-O-N glass containing 17 eq% N were studied using a two stage nucleation and growth treatment. Both classical and differential thermal analysis techniques were used and were found to be in close agreement. The results indicate that Tg+40K and Tc-2-40K to be the optimum nucleation and crystallisation temperatures respectively, with a maximum volume fraction of crystalline phases and a smaller crystal size. The major crystalline phases present are mixtures of different forms of yttrium disilicate and silicon oxynitride. The activation energy for the crystallisation process was found to be 834KJ/mol. The influence of sample specific surface on the devitrification mechanisms have been estimated and bulk nucleation has been proposed to be the dominant nucleation mechanism.