Oxidation of beryllium-a scanning Auger investigation

Beryllium is considered to be a candidate material for the first wall of nuclear fusion plasma experiments, e.g. ITER. In this application, the interaction of beryllium with oxygen is important for two reasons. One aspect is the reaction of hot beryllium with air in case of a catastrophic leak, the other is the action of beryllium as a getter, binding oxygen impurities and thus helping to keep the level of contamination in the plasma low. We therefore investigated the interaction of beryllium with air at elevated temperatures up to 600 deg. C on a microscopic level, using a high resolution Auger electron microscope. At 390 deg. C, a thin protective oxide film is formed, while at 500 deg. C oxidation starts to enter into the grain boundaries, leading to the loosening of small particles of beryllium already at 600 deg. C. The expected diffusion of oxygen from the surface into the bulk has not been observed up to 390 deg. C, the highest temperature to be safely applied inside the Auger microscope. Exposure to hydrogen atmosphere showed no change up to 600 deg. C, exposure to hydrogen plasma resulted in an equilibrium thickness of the oxide layer, which is most likely due to impurities in the plasma. Thus, an operation of beryllium liners as a non-evaporable getter is not to be expected in this temperature range. Getter activity linked to the transport of beryllium from the liner to some deposition areas is, however, possible