Study on Oxidation Behavior of (W,Mo)Si<sub>2</sub> Powders in Air at 400, 500 and 600°C

Abstract

The oxidation of (W,Mo)Si2 powders has been examined at 400, 500 and 600°C for 12.0 hours in air. It was shown that the low temperature oxidation resistance of (W,Mo)Si2 was worse than that of MoSi2, and they showed great changes in mass, volume and colour. At 500°C, the amount of volume expansion of (W,Mo)Si2 was as high as about 7~8 times and color changed from black to yellow after 4.0h with MoO3, WO3, (W,Mo)O3 and amorphous SiO2 as main reaction products. It took about 8.0h to obtain the same results for MoSi2. The mass gain and oxidation rate were relatively slower at 400°C and 600°C than that at 500°C. These were probably due to the lower oxidation rate at 400°C and the protective silica glass on surface of powders formed from the volatilization of MoO3, WO3 and (W,Mo)O3 at 600°C, which would restrain the diffusion of molybdenum from matrix to exterior and oxygen from outside to inside and the further accelerated oxidation.