| Nanocrystalline Nd-Fe-B powder was prepared by a new R-D process using fine spray-dried precursors. For this process, Ca reduction that is the most important step for the formation of hard magnetic Ne2Fe14B was performed in powder state instead of conventional cake state. When the calcium-reduced powder was washed to remove the byproduct CaO in distilled water, NH4Cl solution, and alcohol, respectively, a violent exothermic reaction was occurred except for alcohol. This violent exothermic reaction resulted in partial decomposition of Nd2Fe14B to soft magnetic Nd2Fe17Bx. Consequently, magnetic properties of the powder washed in distilled water or NH4Cl solution were considerably reduced mostly due to such phase decomposition by the increase of reaction temperature. |
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