Hydrogen permeation characteristics of V–Ni–Al alloys

We prepared a series of V–(15−x)Ni–xAl (0.09⩽x⩽4.5) alloys by arc melting and investigated their hydrogen permeation characteristics using palladium-coated disk samples. In x⩽0.9 alloys, precipitates of the sigma phase were observed in the matrix of the bcc phase. In alloys with higher Al content, a single bcc phase was observed. The hydrogen permeability increased in parallel with the Al content at temperatures higher than 473 K. The hydrogen permeability of the V–10.5Ni–4.5Al membrane was 6.29×10−8 mol H2 m−1 s−1 Pa−1/2 at 623 K, or about twice that of the V–15Ni membrane. The hydrogen diffusivity was only weakly dependent on the Al content, hence the increase in the hydrogen permeability in parallel with the Al content was concluded to be mostly due to the increase in hydrogen solubility. The hydrogen permeability of the V–10.5Ni–4.5Al membrane decreased to 59% of the initial value during a permeation test conducted for 102 h. However, a subsequent baking treatment with air introduced into the permeation system resulted in a complete recovery of the hydrogen permeability to the initial value.