Formation of Sm–Fe Intermetallic Compounds by the Reduction-Diffusion Process with CaH<SUB>2</SUB>

Abstract

In order to clarify the rate and mechanism of the formation of Sm–Fe intermetallic compounds by the reduction-diffusion (R-D) process, three kinds of experiments were carried out: (1) the reduction of pellets of Sm2O3 powder mixed with CaH2, (2) the R-D reaction for the pellets which were composed of Sm2O3, CaH2 and Fe (powder or wire) at 1300, 1400 and 1500 K, and (3) diffusion experiment by using Sm–Fe diffusion couples with Mo wire as a marker at 963 K.The reduction of Sm2O3 uniformly proceeded in the pellets; more than 90% of Sm2O3 was reduced at 1400 and 1500 K in a reaction time less than 1 ks, though about 80% at 1300 K at a reaction time of 1 ks. During the R-D reaction, a Sm2Fe17 layer was formed on the Fe surface. The thickness of the Sm2Fe17 layer grew according to a parabolic rate law at 1300 K. At 1400 and 1500 K, however, the Fe dissolved in a liquid Sm or Sm–Ca melt, since the reduction rate of Sm2O3 was high. The experiment with the diffusion couple revealed that Fe diffused faster than Sm in the SmFe2 layer.