Influence of Aluminum and Mischmetal on Cyclic Response of Ca-Ni Based Alloys in Hydrogen with Oxygen as Impurity

Abstract

The additional effects of Mm and Al on the hydrogen desorption properties of CaNi₅ were studied from hydrogen absorption-desorption cycles in hydrogen containing 300 ppm O₂. It turned out that the hydrogen discharge ratio of Ca_1−xMm_xNi_5−yAl_x(x=0, 0.3 and y=0, 0.1) alloys decreased in the early cycles, but after that it gradually increased because of the self-restoring mechanism for the degradation of hydrogen discharge ratio. The self-restoration was slower in the case of the addition of both Mm and Al than in the case of the addition of Mm only.
Auger electron spectroscopy revealed that the content of Ca increased in the surface of allays exposed to 1200 Pa O₂. The addition of Al caused the structure just under the Ca-rich layer to be poor in Ca content.