Abstract
In relation to the joining of silicon nitride ceramics to metal, the kinetics of reaction between Si3N4 and W has been investigated in Ar and N2 at temperatures from 1473 to 1673 K. Using an Si3N4-W powder mixture, the reaction rate was determined with a thermobalance, and the reaction products were examined by X-ray diffraction. The reaction between Si3N4 and W started at 1473 K in Ar, but not in N2. Tungsten nitride was not detected regardless of the atmosphere. Tungsten suicide W5Si3 was produced only in Ar, and it changed to WSi2 at higher temperature and on prolonged heating. The initial rate obeyed the linear rate law and the activation energy was 278kJ·mol-1. The rate-determining step is considered to be the chemical reaction at the interface between Si3N4 and W. At a late stage of reaction, the kinetics followed the parabolic rate law and the activation energy was 281kJ·mol-1. The reaction rate is probably controlled by the solid-state diffusion through the product layer.
