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pp.197-202
A novel route to prepare Nd-Fe-B magnetic particles by utilizing both spray drying and reduction/diffu- sion processes was investigated in this study. Precursors were prepared by spray drying method using the aqueous solu- tions containing Nd salt, Fe salt and boric acid with stoichiometric ratios. Precursor particles could be obtained with various sizes from 2 to 10 µm by controlling concentrations of the solutions and the average size of 2 µm of precursors were selected for further steps. After heat treatment of precursors in air, Nd and Fe oxides were formed through desalt- ing procedure, followed by reduction processes in Hydrogen (H2) atmosphere and with Calcium (Ca) granules in Argon (Ar) successively. Moreover, diffusion between Nd and Fe occurred during Ca reduction and Nd2Fe14B particles were formed. With Ca amount added to particles after H2 reduction, intrinsic coercivity was changed from 1 to 10 kOe. In order to remove and leach CaO and residual Ca, de-ionized water and dilute acid were used. Acidic solutions were more effective to eliminate impurities, but Fe and Nd were dissolved out from the particles. Finally, Nd2Fe14B magnetic particles were synthesized after washing in de-ionized water with a mean size of 2 µm and their maximum energy prod- uct showed 9.23 MGOe.
