Abstract

The structural and magnetic properties were studied for recycling Nd–Fe–B powders from Nd–Fe–B sintered magnets sludge via reduction diffusion (RD) with calcium hydride (CaH2) particles. For comparison, traditional reducing agent calcium granules were applied to prepare recycled Nd–Fe–B powders. Finer particle size and better size distribution as well as lower impurity content are achieved by using CaH2 instead of Ca. In detail, the average particle size of the recycled Nd–Fe–B powder is reduced from 4.66 to 3.43 μm, and the bimodal distribution disappears. Moreover, the residual calcium content and oxygen content are reduced to about 0.080 wt% and 0.32 wt%.

As a consequence, the room-temperature magnetization of the CaH2-recycled Nd–Fe–B powder is increased to 146.30 emu/g, 6.8% and 33%, respectively, higher than that of Ca-reduced powder and the initial sludge. Further analysis indicates that CaH2 is able to reduce the sludge at lower temperature to fabricate well-dispersed, uniform recycled powder with high magnetization arising from a combination factors of its low melting point, low thermodynamic behavior, and the release of hydrogen during the reaction.