High energy product Nd-Fe-B sintered magnets produced by wet compacting process

High energy product ((BH)_max) Nd-Fe-B sintered magnets can be produced by the wet compacting process. In the wet process, the milled powders are mixed in a mineral oil to the slurry and the slurry was compacted in the magnetic field. In order to improve the alignment of powders, some lubricants were added to the slurry for the reduction of friction between grains and/or the dispersion of grains. At first, a surface-active agent of nonion type was examined, with the result that the residual magnetization (Br) was increased by 0.02 T with the improvement of the grain alignment, while the coercivity (N_cJ) decreased by 0.1 MA/m. The chemical structures of lubricants were studied to reduce the decrease of H_cJ and the requirements for suitable lubricants were found out. By the addition of the methyl oleate, the high performance magnets with (BH)_max=409 kJ/m³ (51.4 MGOe), Br=1.46 T (14.6 kG), H_cJ=1.20 MA/m (15.1 kOe) were obtained in mass-production