Low-temperature nitride transformation reactions

This study illustrates a novel method of transforming between two refractory nitrides at temperatures well below their respective melting points. Silicon nitride (Si ₃N ₄) is an excellent thermal and electronic insulator, with applications in the microelectronic, automotive and technical ceramic industries. Thermodynamically, there is a significant decrease in the Gibb's Free Energy inherent in the transformation between Si ₃N ₄ and a number of refractory metal nitrides; however, these transformation reactions are limited in the pure state by a kinetic barrier at any temperature appreciably lower than the melting point of Si ₃N ₄ (∼2173 K). Results of this study illustrate the successful conversion of powdered amorphous Si ₃N ₄ to TiN. The transformation is made possible by a liquid phase present in a number of Ti-based alloys at temperatures in the vicinity of 800°C. Since both nitrides (SiN _x and TiN) are refractory, the presence of the liquid phase provides a high-diffusivity pathway, thus overcoming the kinetic barrier associated with the otherwise thermodynamically favorable reaction.