Development of Methods of Deposition of Discontinuous Nickel Coatings on Powders of AB5 Type Alloys

In the present work, the possibility to modify the surface of the intermetallic compound MmNi₅ (Mm — La_0.815Ce_0.185) by nickel during decomposition of nickel oxalate (C2O4Ni) either during reducing heating in hydrogen or during intensive grinding in a planetary ball mill was investigated. The phase composition and transformation of the alloy lattice depending on conditions were controlled by X-ray diffractometry. Reducing heating in hydrogen products and grinding products of mixtures of the alloy with nickel oxalate contain the second phase, namely, elemental Ni. In the case of milling with nickel oxalate, particles and clusters of the Ni phase were smaller, uniformly distributed on the surface of alloy particles, and did not form a continuous coating. The lattice volume remains unchanged for powders ground in vacuum or air and increases by 1% and 5% for those ground in Ar and H₂, respectively. It was made the assumption of the preferred location of hydrogen atoms between hexagonal planes along the axis c. After mechanical treatment, the discharge capacity of the MmNi₅ alloy increases by 20%, and the combination of grinding and coating by Ni does not enhance this effect. The catalytic activity of the alloy surface modified by Ni during grinding in Ar is higher than that after grinding in air by 10–15%.