Kinetics of Reaction between Si<sub>3</sub>N<sub>4</sub> and Mo

Abstract

The kinetics and the mechanism of the reaction between Si3N4 and Mo have been investigated in N2 or Ar stream at temperatures from 1273 to 1573K. Using a Si3N4-Mo powder mixture, the reaction rates were determined with a thermobalance, and the reaction products were examined by X-ray diffraction. The reaction between Si3N4 and Mo began after heating to about 1450K in N2 stream or about 1250K in Ar stream. In Ar stream, MoSi2 was also produced in addition to both Mo3Si and Mo5Si3 which were the reaction products in N2 stream, whereas Mo nitrides were not detected even in N2. At higher temperatures and on prolonged heating, the silicide changed from Mo3Si to MoSi2 via Mo5Si3. The initial rate followed a linear rate law, and the rate constant k1 in N2 was smaller than that in Ar. Furthermore, the activation energies were 600kJ/mol in N2 and 344kJ/mol in Ar. From a detailed analysis of the kinetic data, an interfacial reaction may be considered as the rate-determining step. At a late stage of the reaction, the kinetics apparently followed a parabolic rate law, and the rate constant kp and the activation energy were significantly changed, depending on the kind of Mo silicide formed as the reaction layer. These results suggest that the reaction rate is probably mixed-controlled by both a interfacial reaction and a solid state diffusion through the reaction layer.