The high-temperature heterogeneous reaction rates of bulk tungsten (W) were studied using thermogravimetric analysis in steam (H2O) and hydrogen (H2) atmospheres. Reaction rates were determined at isothermal conditions for temperatures ranging from approximately 1100 to 1700°C. Constant system pressures of 1 atm were employed; however,H2Opartial pressures ranged from 3.04 to 51.3 torr. Using Arrhenius reaction rate kinetics, the activation energy of the tungsten-H2O oxidation reaction was calculated to be 51 kcal=mol, while theH2Opressure exponent, or reaction order, was determined to be 0.82. Increasing concentrations of H2 were found to exponentially reduce the desorption rates of the tungsten oxides involved in the oxidation reaction. Addition of H2 slightly reduced the apparent activation energy of the reaction as well, indicating a stronger inhibiting effect at higher temperatures. The derived oxidation rates indicate that, under most rocket motor conditions, corrosion of tungsten nozzles are most likely limited by gas-phase diffusion of oxidizers to the nozzle surface and/or lack of available reaction sites (i.e., surface area limited or pressure independent).
All Science Journal Classification (ASJC) codes
- Aerospace Engineering
- Fuel Technology
- Mechanical Engineering
- Space and Planetary Science