Abstract

A novel route to prepare Nd-Fe-B magnetic particles by utilizing both spray drying and reduction/diffusion processes was investigated in this study. Precursors were prepared by spray drying method using the aqueous solutions containing Nd salt, Fe salt and boric acid with stoichiometric ratios. Precursor particles could be obtained with various sizes from 2 to 10µm by controlling concentrations of the solutions and the average size of 2µm of precursors were selected for further steps. After heat treatment of precursors in air, Nd and Fe oxides were formed through desalting procedure, followed by reduction processes in Hydrogen (H_2) atmosphere and with Calcium (Ca) granules in Argon (Ar) successively. Moreover, diffusion between Nd and Fe occurred during Ca reduction and Nd_2Fe_14B particles were formed. With Ca amount added to particles after H_2 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, Nd_2Fe_14B magnetic particles were synthesized after washing in de-ionized water with a mean size of 2µm and their maximum energy product showed 9.23 MGOe.

• Keywords: Magnetic materials;Nd-Fe-B magnetic powder;Magnetic properties;Reduction/diffusion process;Washing;