Abstract
Adsorption of hydrogen on a clean niobium surface and the absorption of hydrogen into the bulk were investigated. The sticking probability of hydrogen on a clean niobium surface was found to be about 0.13. Evidence for a precursor surface adsorption state and subsequent diffusion into the bulk was found; the sticking probability is independent of temperature when the surface is clean but becomes temperature dependent at higher coverage. The solubility studies indicate ideal interstitial solution obeying Sievert’s law at concentrations of dissolved hydrogen below 0.1 at.% but show deviation from this ideal solution above 0.5 at.%. The heat of solution was found to vary from −16 to −10 kcal/mol. The resistivity of niobium depends on hydrogen concentration and also on temperature and time. The deviations from ideal solution agree with a hydrogen cluster model.
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