High temperature oxidation of tungsten wires in water vapor-argon mixtures

The high temperature oxidation of tungsten wires in free convection was measured in water vapor-argon atmospheres in the temperature range between 2450 and 3000°K and in the H2 O partial pressure range between 3.39 × 10-5 and 1.82 × 10-4 atm at 0.789 atm total pressure. The rate of the reaction generally decreases with increasing temperature at constant bulk water vapor pressure. This dependence is similar to that previously measured in O2-argon and CO2-argon atmosphere. The overall oxidation reaction is gas transport controlled as demonstrated by supplemental measurements at 0.395 atm total pressure. A volatile oxide counter diffusion model, which has been previously proposed to explain the oxidation in O2-and CO2-argon, is in good agreement with H2O-argon experiments. A comparison of the present results with the previous experiments shows that the model is in agreement with the relative magnitude of the oxidation rates measured in the three oxidizing atmospheres.