Bcc V-Fe alloys for the hydrogen separation membranes: Hydrogen solubility and global character of alloying effect

The membranes of V-alloys are a promising alternative to Pd-alloy membranes for ultrapure hydrogen extraction. The hydrogen solubility in V-xFe alloys (x = 3.5, 4.0, 7.1, 8.8, and 13.1 at. %) was experimentally investigated in the pressure range of 10 Pa to 1.2 x 10(6) Pa, temperature range of 250 degrees C-450 degrees C, and hydrogen concentration, H/M, range of 0.004-0.65. When used as an alloying element, Fe inhibited the hydrogen solubility in V in the same way as Pd does, but significantly stronger than other elements. Hydrogen dissolution in V-xFe alloys followed Sieverts' law considerably beyond the pressure range of diluted solution. The decrease in the hydrogen solubility constant caused by alloying V with Fe was found to be caused by an increase in enthalpy of hydrogen solution, whereas the pre-exponential factor remained the same as in pure V. In addition, the highest concentration of absorbed hydrogen that can be attained in the phase of hydrogen solid solution was virtually equal to that in pure V. These findings suggest that the effect of alloying V with Fe on hydrogen solubility has a purely global character: the interstitial sites in the bcc lattice of V-xFe alloys are equivalent, regardless of whether their adjacent environment contains Fe atoms.

Automated summary

The study investigates the solubility of hydrogen in V-xFe alloys and finds that Fe has a stronger inhibitory effect on the solubility compared to other elements. Hydrogen dissolution in V-xFe alloys follows Sieverts' law and the effect of alloying V with Fe on hydrogen solubility is mainly attributed to an increase in enthalpy of hydrogen solution.