Reaction of Mo2C, W2C, WC and WC-Co with Oxygen at High Temperatures.

The reaction of molybdenum and tungsten carbides and WC-Co alloys with oxygen at pressures of 10** minus **4 to 40 mbar and temperatures of 1300 to 2100 K was gravimetrically determined and the formation of carbon monoxide was checked by measurements of partial pressure. Metallic surface layers are formed on the carbides when the reaction leading to the formation of carbon monoxide is fast. The growth rate of the metal layer depends on the diffusion of carbon in the metal. Volatile oxides form and evaporate from this layer and this, in turn, reduces the layer thickness. These two overlapping reactions finally reach a steady state with constant weight loss and constant metal layer thickness. The process can be described quantitatively by known data for the diffusion of carbon and for the vaporization rates of volatile oxides. Theoretical calculations and experiments results are in good agreement. The weight loss curves of the WC-Co alloys show additional effects due to the evaporation and/or oxidation of cobalt, especially at higher temperatures and oxygen pressures. Refs.