Mass-Spectrometric Investigation of the Oxidation of Molybdenum and Tungsten

The oxidation of molybdenum and tungsten was investigated mass spectrometrically at temperatures between 1500° and 2600°K and oxygen pressures between 10—4 and 10—2 Torr. The principal products of oxidation were found to be the gaseous dioxide and trioxide, MO2(g) and MO3(g) (M=Mo or W). The trioxide is the more important species at low temperatures; the dioxide is the dominant product at high temperatures. Small amounts of polymeric oxides, (MO3)2(g) and (MO3)3(g) were formed at the lowest temperatures and highest oxygen pressures. The gaseous oxidation products are not in equilibrium with a solid surface oxide.