急冷凝固(Ni0.6Nb0.4)70Zr30 アモルファス合金の水素透過性に対する表面被覆元素の影響

Abstract

The effect of surface coating element on hydrogen absorption and permeation of the (Ni0.6Nb0.4)70Zr30 amorphous alloy membrane was investigated. As a result, it was found that the Ni-coated sample exhibited a much slower hydrogen absorption rate than the Pd-coated sample. However, both types of sample showed same hydrogen absorption content after saturation. The Pd-coated sample showed hydrogen permeation one order of magnitude larger than Ni-coated sample. The pressure dependence of permeation flux was also investigated and it was found that the rate controlling factor of hydrogen permeation in the Pd-coated sample and in the Ni-coated sample was hydrogen diffusion in the alloy and surface reaction, respectively. It was also found that the permeability of the samples with Ni and Pd on the upper-side (retentate side) and the lower-side (permeate side) surfaces, respectively, was smaller than that of the Pd-coated samples, comparing those two types of the sample having the Pd coating layer on the lower-side surface of the membrane. This is because the hydrogen concentration gradient in the sample with Ni and Pd on the upper-side and the lower-side surfaces, respectively, is smaller than that in the Pd-coated sample due to the smaller solubility of hydrogen in the Ni coating layer than in the Pd coating layer. Furthermore, it was found that the element deposited on the lower-side surface of the membrane affected the promotion of hydrogen permeation more significantly than that on the upper-side surface. In this study, the hydrogen permeation of the sample with Ni coated on the lower-side surface of the membrane was much smaller than that with Pd on the lower-side surface. This observation suggests that the recombination of two H atoms and emission of H2 molecules from the lower-side surface can be the significant barrier to hydrogen permeation. Therefore, it was concluded that the hydrogen concentration gradient in the matrix membrane and the reaction on the lower-side surface affected the hydrogen permeability of the membrane sample.