Abstract
A comparison has been made of the microstructure in β′(SiAlON) ceramics sintered with an Sc 2O 3 densifying aid with that of β′ ceramics previously fabricated with Y 2O 3. A parallel study has been made of glasses in the Sc 2O 3Al 2O 3SiO 2 system and of variations in the crystallization products with the addition of nitrogen. The purpose of this study was to explain the crystallization behaviour of the matrix glass in β′ ceramics. Crystallization of the matrix in β′ ceramics as thortveitite (ScSi 2O 7) and a silicon-substituted form of (Sc, Al) 2O 3 may be rationalized with a similar behaviour for the bulk glasses which contain a maximum nitrogen solubility (about 8 at.% N). The temperature of the Sc 2O 3Al 2O 3SiO 2 eutectic, on which sintering liquids are based, is higher than in the related Y 2O 3 system. This is the basis for the improved high temperature oxidation of β′ ceramics containing Sc 2O 3.
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