FORMATION OF BETA'-SIALON IN THE AL-SIO2-N2 SYSTEM

Reaction processes which form beta'-sialon by reaction between SiO2 and Al in an N2 atmosphere up to 1440-degrees-C were studied by means of DTA and X-ray diffraction techniques. Stoichiometric mixtures of Al and SiO2 powders, for the oxidation-reduction reaction 4Al+3SiO2 --> 3Si+2Al2O3, and mixtures containing 50% Al in excess were used. With the stoichiometric mixture, as well as beta'-sialon, the X sialon phase and mullite were formed as minor constituents. In contrast, the mixture containing Al in excess produced as secondary phase a 15R sialon phase or "Y" phase. The addition of Al in excess made it possible to obtain a product enriched in beta'-sialon.