Kinetics of Reaction between Si<sub>3</sub>N<sub>4</sub> and Cr in N<sub>2</sub> Atmosphere

Abstract

The kinetics and the mechanism of reaction of Si3N4 with Cr have been investigated in an atmosphere of N2. Using powder mixtures of Si3N4 and Cr, the reaction rates were measured by means of a thermobalance at temperatures from 773K to 1573K, and reaction products were examined by X-ray diffraction. Below 1423K, N2 gas reacted with Cr particles to produce Cr2N and CrN. Above 1473K, Cr nitrides were produced at the initial stage of the reaction, and a CrSi solid solution and Cr3Si were formed on the nitride layer at the late stage. The initial reaction followed the linear rate law. Below 923K, the activation energy was 35kJ/mol and the rate-determining step was the diffusion of N2 to the surface of the Cr partides. Above 973K, the activation energy was 202kJ/mol and the rate was probably mixed-controlled by the gaseous diffusion and the interfacial reaction. When the Cr particles were covered with the reaction products, the kinetics was described by the parabolic rate law. The activation energies were 148kJ/mol below 1273K and 305kJ/mol above 1323K. The solid State diffusion through the reaction layer may be considered as the rate-determining step.