Abstract
Nd-Fe-B alloy powder was granulated by a spray drying method using an organic binder in order to improve the powder flowability during feeding and compacting. In this experiment, the organic binder consisted of poly(methyl methacrylate) (PMMA) and di-n-butyl phthalate, and 1, 4-dioxane as a solvent was used in granulating process, to suppress the residual moisture content in granulated powders and the reaction of alloy powders with its moisture, which result in marked degradation in powder characteristics and magnetic characteristics, respectively. By increasing the additional polymer content, powder characteristics were improved. However in comparison with the case of aqueous binder consisted of poly(vinyl alcohol) (PVA) and plasticizer, powder characteristics lowered slightly because of lower tensile strength of PMMA than PVA. In the case of PMMA the residual moisture contents in granulated powders were much smaller than those of PVA, independently of additional polymer content. The residual oxygen contents of green bodies after debinding were also smaller than those obtained using PVA. By using PMMA the magnetic characteristics (remanences and maximum energy product) of sintered magnets were improved remarkably, as compared with those of PVA. These facts mean that the high magnetic characteristics would be caused by both using low tensile strength polymer and restraining oxidation reaction of alloy powders.
