Oxidation and volatilization of TZM alloy in air

The excellent high temperature strength and thermal conductivity of molybde num-base alloys provide attractive features for components in advanced magn etic and inertial fusion devices. Refractory metal-base alloys react readil y with oxygen and other gases, and molybdenum alloys are susceptible to los ses from highly volatile molybdenum trioxide (MoO3) species. Transport of r adioactivity by the volatilization, migration and re-depssition of MoO3 dur ing a potential accident involving a loss of vacuum or inert environment re presents a safety issue. We have experimentally measured the oxidation, vol atilization and re-deposition of molybdenum from TZM in flowing air between 400 degreesC and 800 degreesC. Calculations using chemical thermodynamic d ata for vapor pressures over pure MoO3 and a vaporization mass transfer mod el correlate well with the experimental data between 600 degreesC and 800 d egreesC. Partial saturation of(MoO3) gas species accounts for influences of flow rate at 700 degreesC. Some anomalies in oxidation rate below 650 degr eesC suggest that other phases, e.g., MoO2 or other non-stoichiometric oxid es may influence oxidation and volatilization processes under some limited conditions. (C) 2000 Elsevier Science B.V. All rights reserved.