Molybdenum and Tungsten Combined Oxidation by Dissociative Evaporation of Products during Refractory Oxides Crystal Growth from the Melt

The main chemical reactions and composition of gas and solid phases have been determined for the equimolar ratio Mo: W: O2 = 1: 1: 2 at T = 2400 K in the pressure range of 1-1 x 10-5 bar. It is established that the character of the main processes of combined oxidation depends significantly on the pressure and state of the oxidant (oxygen): at P > 7.52 x 10-5 bar, oxidation reactions involve mainly molecular oxygen, whereas atomic oxygen dominates at lower pressures. At P ≥ 0.424 bar, the solid phase contains not only Mo but also MoO2. At P = 1 x 10-5 bar, the concentration of lower Mo and W oxides and elementary Mo and W in the gas phase sharply increases, which can negatively affect the main crystallization units.