Effects of surface impurity layers on the hydrogen permeability of vanadium

Surface impurity layers were found to reduce the hydrogen permeability of vanadium by a factor of several hundred over the temperature range from 200 to 8500C. These impurity layers formed during hydrogen permeation studies that were carried out over periods of approximately 1500 h under conditions where the ultimate vacuum ranged from approximately 10-5 to 10-8 torr. Studies using Auger, ion microprobe, and nuclear microprobe methods showed that the major impurity elements on the surface of contaminated vanadium samples were oxygen and carbon. The depth of penetration of oxide into the vanadium due to diffusion was found to be in excess of 10 μm. Hydrogen permeation rates determined for surface-oxidized vanadium samples appeared to have a half-power dependence on upstream hydrogen pressure. The implications of these results with respect to the use of vanadium as a structural or clad material in fission and fusion reactors are discussed. (Auth.)