カルシウムによる混合希土酸化物の還元拡散反応

還元拡散法によるニッケル-ミッシュメタル系化合物の直接製造に関する研究 (第1報)

抄録

Aiming at the development of a less energy-consumptive process for producing hydrogen storag materials, an experimental study was carried out on the direct production of Ni-Rm (Rm: mixture of La, Ce, Pr and Nd) compounds from the mischmetal oxides by the reduction-diffusion (R-D) method. In the R-D process, a mischmetal oxide was reduced by metallic calcium at temperatures of 950, 1, 000 and 1, 050°C in the presence of nickel particles (size:-100, +200 mesh) and the reduced mischmetal elements diffused into the particles to directly form a Ni₅Rm compound.
An optical microscopic observation and an EPMA analysis of the reacted nickel particles revealed that three layers of Ni₄Rm, Ni₅Rm and Ni₅Ca were formed topochemically from outside to inside the particle, and that the Ni₅Ca layer was always sandwiched between the Ni₅Rm layer and the unreacted nickel core, suggesting that a reaction of the diffused mischmetal elements with Ni₅Ca to form Ni₅Rm, Ni₅Ca+ Rm=Ni₅Rm+ Ca, occurred. Volume fractions of the Ni₄Rm and Ni₅Rm layers, which were determined for the particles with an average diameter of 200 pm, using an image analyzer, were found to rapidly increase with the reaction time, and the unreacted nickel disappeared in 135, 55 and 45 minutes at 950, 1, 000 and 1, 050°C, respectively.
The experimental results were discussed based on the unreacted core model and a reactive diffusion mechanism, focusing on the role of Ni₅Ca which enhanced the rate of formation of Ni₅Rm.