High Pressure Oxidation of Metals: Tantalum in Oxygen

The temperature and pressure dependence of the reaction of tantalum in oxygen were investigated from 500° to 1000°C at pressures from 10 mm Hg to 600 psi total oxygen pressure. Tantalum was found to oxidize linearly under the above conditions. Three distinct regions of temperature dependence were found with different energies of activation. From 500° to 600°C the rate of oxidation of tantalum was found to be essentially independent of the oxygen pressure at the pressure investigated. The oxidation rate increases rapidly with an increase in pressure from 600° to 800°C. The dependence of the oxidation rate on the bulk concentration may be expressed by V = k′θ, where k′ is the specific rate constant and \(\theta=k_1C_{\text{O}_{2}}/(1+k_1C_{\text{O}_{2}})\), where k₁is the equilibrium constant for the adsorption of oxygen on tantalum.