High-Temperature Heterogeneous Reaction Kinetics of Tungsten Oxidation by CO2, CO, and O2

The high-temperature heterogeneous reaction rates of bulk tungsten are studied using thermogravimetric analysis in oxygen (02), as well as carbon dioxide (CO(2)) and carbon monoxide (CO) atmospheres. Isothermal reaction rates were determined at temperatures ranging from 1300 to 1700 degrees C. Constant system pressures of 1 atm were employed; however, O(2) and CO(2) partial pressures ranged from 0.152 to 3.8 torr and 7.6 to 64.6 torr, respectively. Using Arrhenius reaction rate kinetics, activation energies or the W-O(2) and W-CO(2) reactions were found to be 23.5 and 64 kcal/mol, whereas pressure exponents were determined to be 0.89 and 0.6, respectively. Oxidation rates were higher for O(2) than CO(2) under constant partial pressure conditions. Increasing CO concentration in the presence of constant CO(2) partial pressure was found to reduce reaction rates significantly, emphasizing the impact gas mixtures may have on heterogeneous reaction rates. The results imply chemical erosion rates of nozzles may be altered significantly by small perturbations in propellant formulations, and O(2) may play a nonnegligible role, even in very small quantities present in rocket motors.