The influence of hydrogen in the nitriding gas on the strength, structure and composition of reaction-sintered silicon nitride

The influence of hydrogen in a “static” and “flowing” nitriding gas on the mechanism of formation, composition, structure and mechanical properties of reaction-sintered silicon nitride has been investigated. Using previously developed structural and compositional models describing the progressive formation of silicon nitride, it is suggested that hydrogen enables a high partial pressure of silicon monoxide to be maintained at the early stages of nitridation, thus promoting the rapid development of a continuous skeletal network of silicon nitride with resultant high strength. The mechanisms of formation, composition, structure and mechanical properties of silicon nitride formed from one type of silicon compact under a variety of nitriding conditions are compared, and the significance of the nitriding atmosphere in determining properties is demonstrated.