抄録
An experimental study was carried out on the reactive diffusion in the Ni-La binary alloys for providing a fundamental knowledge of the reduction-diffusion (R-D) method to directly produce powders of nickel-rare earth compounds RNis for use of hydrogen storage materials.
Phase relationships were investigated at temperatures above 1, 100K and in the concentration range of nickel above 60 mol%, using reactive diffusion and metallographic methods. New compounds of LaNi4 and La2Nis5 were found in the process of reactive diffusion. Peritectic reactions relating to these compounds were L+LaNis→LaNi4 at 1, 408K, L+LaNi4→La2Ni7 at 1, 373K and L+LaNi3→La2Ni5 at 1, 153K. Solubility limit of a LaNis solid solution was determined by an EPMA analysis, and the maximum solubility was 82.4-85.6mol% Niat 1, 543K.
Interdiffusion coefficient D of the LaNi5 compound was determined in the temperature range from 1, 423 to 1, 503K, using a diffusion couple, and was given as D/m2·ES-1=1.02×10-1·Eexp (-294 kJ·Emol-1/RT) with activation energy of 294 kJ·Emol-1 (R: gas constant).
Diffusion experiments using a diffusion couple of Ni/CaNi5/Ni-La melt were carried out to investigate a role of the CaNis thin coating layer on the surface of the metallic nickel, which drastically enhanced the reactive diffusion to form the LaNi5 compound.
