CATALYTIC EFFECT OF COBALT ON THE CARBURIZATION KINETICS OF TUNGSTEN

The kinetics of the gas-phase carburization of tungsten by methane were studied and found to be controlled by two surface reactions and a later diffusion limiting reaction. The two surface reactions were found to produce the compounds W2C and W2C-WC respectively. The diffusion limiting reaction produced only WC. Extensive carburization caused cracking of the tungsten material. Cobalt was found to form a thin film on each tungsten surface which was easily converted to eta-phase (Co3W3C) when carburization began. A model was proposed and kinetic equations were developed which predict the rate of reaction for both cylinders and powders. The reaction rate curves for the uncatalyzed reaction using the same equations was also developed. © 1979 American Society for Metals and the Metallurgical Society of AIME.