The chemical action of oxygen on a heater during growth of refractory oxide crystals from melt

The behavior of the W-O₂ system has been investigated at 2400 K in the pressure range from 1 to 1 × 10^?5 bar. The chemical composition of the solid and vapor phases for the ratio W: O₂ = 1: 1 was calculated by minimizing the Gibbs free energy. It is shown that the only solid phase in the system is metallic tungsten (0.333–0.355 mol), whereas trioxide WO₃ dominates in the vapor phase; its concentration may reach 99%. It is concluded that providing an inert atmosphere in the growth chamber with a pressure of 1 bar decreases the concentration of atomic and molecular oxygen in the vapor phase and decreases its effect on the tungsten heater.