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 (Si₃N₄) 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 Si₃N₄ 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 Si₃N₄ (~2173 K). Results of this study illustrate the successful conversion of powdered amorphous Si₃N₄ 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.