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 1573K. 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 1450K in N
2 stream or about 1250K 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
k1 in N
2 was smaller than that in Ar. Furthermore, the activation energies were 600kJ/mol in N
2 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.
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