Rhenium oxidation by steam at high temperature
Oxidation of metals, Vol. 61 (1/2), pp. 49-67.
We have studied the kinetics of rhenium oxidation, under flowing steam + argon mixtures, at atmospheric total pressure and steam partial pressure in the range 24-74 kPa, and at temperatures from 1600°C up to 2200°C. No regime change was observed in the temperature dependence of the oxidation rate, which shows that the chemical regime extents up to the highest temperature investigated. However, at 2025°C, the oxidation rate has been found to depend also on the gas mixture velocity, revealing that, for the conditions used, mass transport processes in the gas phase also act as a limiting factor. We thus encountered at high temperature a mixed control regime. We also observed at high temperature a strong dependence of the oxidation rate with the steam partial pressure. Thus, we suggest the mass transport limiting factor to be the steam diffusion through a volatile oxides gaseous layer above the rhenium surface.