As a basic study for the application of the reduction-diffusion (R-D) process to the production of Sm₂Co₁₇ type magnet materials, reduction reactions of Sm₂O₃ and ZrO₂ by matallic Ca, and the effects of requisite elements for the materials on the reactions were investigated by the differential thermal analysis. When Sm₂O₃ or ZrO₂ alone was reduced, the reduction reaction began immediately after the fusion of Ca as has been reported for the case of the reduction of Nd₂O₃ by metallic Ca. When they were reduced in the presence of the requisite elements, however, Cu has a distinct effect to lower the reduction rate of Sm₂O₃, the reason of which has been attributed to the gradual formation of a Cu-Ca melt necessary to cause the reduction and also to the decrease in Ca activity due to the melt formation.
A Sm₂O₃ block prepared by arc-melting Sm₂O₃ powder was reduced by Ca vapor to study the effect of CaO formed on the block during the reduction reaction. It has been found that the CaO layers formed on the Sm₂O₃ block were porous and did not obstruct the passage of Ca vapor. The formation mechanism of the porous CaO layers has been discussed and compared with the formation mechanism of dense CaO which plugs pores in a porous rare earth oxide pellet. Further, it has been concluded that, in the actual R-D process, the reduction reactions of rare earth oxides may not be hindered by the formed CaO.