On the mechanisms associated with the chemical reactivity of Be in steam

One safety concern surrounding beryllium as a plasma-facing material in a water-cooled Tokamak is steam interactions with hot beryllium and the production of significant quantities of hydrogen. We have tested several different product forms of Be with different densities and levels of porosity. Oxidation kinetics has been determined by measurements of hydrogen release with a mass spectrometer, volumetric measurements of the product gas and weight change of the sample. We discuss and compare with the literature the fundamental mechanisms and kinetics controlling the oxidation of Be in steam. Fully dense beryllium exhibits parabolic, linear and accelerating modes of oxidation as temperature increases from 450°C to 1200°C. The oxidation mechanisms and temperature trends are similar for other product forms. Oxidation rates are higher, however, when processing or annealing significantly increases the extent of interconnected porosity and consequently the effective surface area. The effective surface area as measured by BET surface analyses is a key parameter when comparing oxidation rates.