Oxidation resistance of carbides in chlorine-containing atmospheres

High temperature oxidation resistance of various carbides was investigated in air and in chlorine containing environments. Thermogravimetric oxidation tests were performed on fine powders of Cr3C2, TiC, TiCN, and WC in N-2-20%O-2 and in N-2-20%O-2 containing 2000 vppm HCl in the temperature range of 200-800degreesC in order to clarify the effect of chlorine containing species on the oxidation resistance of these carbides. The presence of chlorine increased the oxidation rate and also shifted the starting temperature of the oxidation process towards lower temperatures. Cr3C2 was the most stable carbide in both atmospheres. Coarse Cr3C2 powder was isothermally exposed to air with and without addition of solid KCl. Solid KCl accelerated oxidation of Cr3C2 significantly. The oxide layer formed on Cr3C2 particles in presence of KCl was porous and brittle, whereas the oxide layer formed on Cr3C2 in air was dense.