Carbothermic reduction of Silica
In this process Silica powder and Carbon powder is heated in a special furnace under nitrogen atmosphere a temperature of 1300 to 1700.C so as to form silicon monoxide. Which is react with nitrogen to form silicon nitride.
The unreacted carbon is removed by oxidation by heating at 500.C in air. In this process highly sinterable silicon nitride powder with very high alpha phase content. Normally impurities like chlorine or carbon may be present in the final product.
To improve the sintering behavior we can add alumina or magnesia as impurities to certain level in the preparation stage itself.
To be contd…..
