In order to elucidate the rate and mechanism in producing Nd-Fe-B magnetic materials by the R-D process, kinetic experiments in a temperature range between 1, 200K and 1, 400K were conducted for pellets composed of Nd2O3 powder, Fe wire of 200μm in diameter and CaH2.
The fractional reduction of Nd2O3 obtained by an X-ray intensity of diffraction increased with time nearly parabolically. The reduction proceeded slowly and it may take about 2 hours to complete the reaction even at 1400K. During the R-D process at 1, 300K, the Nd2Fe17 layer was formed on the surface of Fe wires and the layer thickness obeyed the parabolic rate law, showing that the diffusion of Nd in the Fe wire controlled the rate. However, the higher temperature of 1, 400K or longer reaction time caused dissolution of Fe in the Nd melt.
