Mechanism of High Temperature Reaction between Si<SUB>3</SUB>N<SUB>4</SUB> and Fe Powders

The kinetics and mechanism of the reaction of Si3N4 with Fe were investigated. Using powdered Si3N4-Fe mixture, the reaction rates were measured by means of a thermobalance at temperatures from 1373 to 1673 K in Ar or N2 gas stream. The reaction products were examined by X-ray diffraction.The reaction of Si3N4 with Fe was initiated after heating to about 1350 K. The reaction product changed from Fe-Si solid solution to Fe silicide Fe3Si, as the reaction proceeded. The reaction rates and the reaction products were independent on the atmosphere. The kinetics obeyed the nearly parabolic rate law. The formation of Fe3Si increased the rate constant abruptly. The apparent activation energy was 533 kJ/mol in the region of Fe-Si solid solution. The reaction rates of Si3N4 with Fe are probably mixed-controlled by both the interfacial reaction and the diffusion through the reaction layer.