Densification of Silicon Nitride: Effect of Chlorine Impurities

The effect of chlorine impurities on the densification of hot‐pressed silicon nitride has been simulated by the addition of chlorine (H 2 PtCl 6 6H 2 O) to the starting powders. The presence of chlorine retards the α‐β phase transformation during hot‐pressing. Microstructurally, it is found that the chlorine is incorporated in the inter granular noncrystalline phase. In the Y 2 O 3 hot‐pressed material, the chlorine appears to prevent the Y 2 Si 2 O 7 phase from crystallizing.