Kinetics of Reaction of Si3N4 with Ni

The kinetics and the mechanism of the reaction of Si3N4 with Ni have been investigated. Using a powdered Si3N4-Ni mixture, the reaction rates were measured by means of a thermo-balance in Ar or N2 gas stream. Reaction products were examined by X-ray diffraction. The reaction of Si3N4 with Ni initiated after heating to about 800K. The reaction product layer was a Ni-Si solid solution below 1073K and nickel silicides above 1123K. The reaction rates and the reaction products were independent of the atmosphere. The initial rate was described by the linear rate law. The activation energy was 118kJ/mol. A chemical reaction may be considered as the rate-determining step. When the Ni particles were covered with the reaction product layer, the kinetics obeyed by the parabolic rate law. The formation of nickel silicide increased the rate constant abruptly. The activation energy changed from 171kJ/mol in a regeon of the Ni-Si solid solution to 214kJ/mol in the regeon of nickel silicide. The reaction rates of Si3N4 with Ni are probably controlled by the diffusion through the reaction layer.