Si₃N₄とMoとの反応の速度論

抄録

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 k_p 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.