The hydrogen permeation through pure niobium metal was investigated using a gas permeation technique, focusing mainly on the measurements in a highly soluble hydrogen state. The hydrogen diffusion was found to be the rate-determining step for the hydrogen permeation reaction. However, the Sieverts law that the hydrogen solubility in a metal is proportional to the square root of hydrogen pressure, was no longer satisfied in the experimental condition of the temperatures of 473 K to 673 K and the applied pressures of 260 kPa at the inlet and 60 kPa at the outlet for hydrogen. This was mainly due to the presence of a large amount of soluble hydrogen in the metal under this condition. As a result, the measured apparent hydrogen permeability decreased monotonously with decreasing temperature in pure niobium. This was completely the reverse of the temperature dependence of the hydrogen permeability in the low solubility state where the Sieverts law was satisfied. It was stressed here that the permeation measurement of hydrogen in the high solubility state was indeed necessary for getting some performance data of metal membranes in practical use.
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Nambu et al. (2005) studied this question.
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