Si_3N_4とMoとの反応の速度論

概要

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The kinetics and the mechanism of the reaction between Si_3N_4 and Mo have been investigated in N_2 or Ar stream at temperatures from 1273 to 1573 K. Using a Si_3N_4-Mo powder mixture, the reaction rates were determined with a thermobalance, and the reaction products were examined by X-ray diffraction. The reaction between Si_3N_4 and Mo began after heating to about 1450 K in N_2 stream or about 1250 K in Ar stream. In Ar stream, MoSi_2 was also produced in addition to both Mo_3Si and Mo_5Si_3 which were the reaction products in N_2 stream, whereas Mo nitrides were not detected even in N_2. At higher temperatures and on prolonged heating, the silicide changed from Mo_3Si to MoSi_2 via Mo_5Si_3. The initial rate followed a linear rate law, and the rate constant k_1 in N_2 was smaller than that in Ar. Furthermore, the activation energies were 600 kJ/mol in N_2 and 344 kJ/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.
社団法人日本セラミックス協会の論文
1993-09-01