Hydrogen Permeation in V-Nb Alloys

Hydrogen permeation and diffusivity in V1−xNbx alloys (x = 0.25, 0.5 and 0.75) were investigated over a temperature range between 573 and 673 K. The alloy sheets surface-coated with Pd (100 nm) by ion-beam sputtering technique were subjected to the hydrogen permeation measurement with hydrogen pressures less than 3000 Pa. It was found that the hydrogen permeation is strongly suppressed especially at low hydrogen pressures; the hydrogen permeation is considered to be controlled by some surface processes. The V0.50Nb0.50 alloy showed the largest permeability 1.4×10−8 mol H2 m−1s−1Pa−1/2 at 673 K which is larger than that for pure Pd. The diffusivity which was determined from the fitting of the permeation curve decreases with the alloy concentration at both the Nb- and V-rich sides and takes a minimum value at x=0.75. The hydrogen potential obtained by a first-principles calculation showed that V atoms act as trapping centers for hydrogen in the Nb matrix and Nb atoms act as anti-trapping centers in the V matrix.