Effect of (C2H5)3NBH3 content on microstructure and properties of Nd-Fe-B nanoparticles prepared by chemical and reduction-diffusion method

This paper reports a novel chemical method to synthesize Nd-Fe-B magnetic nanoparticles. The fabrication mechanism of the particles have been studied through understanding formation of the corresponding intermediate phases as well as their microstructures after annealing and reduction-diffusion processes as function of the (C2H5)(3)NBH3 content. Nd-Fe-B intermediate phases were composed of small Fe3O4 particles and Nd and Fe microcrystals encapsulated with nitriles. Fe3O4 was reduced by BH3- into alpha-Fe as the (C2H5)(3)NBH3 content increased. After annealing, Nd-Fe-B oxide particles gradually agglomerated as the (C2H5)(3)NBH3 content increased, which affected the particle sizes after the reduction-diffusion step. Mixture of Nd2Fe14B and H5Nd2 was obtained from precursors synthesized with 1.5 and 2.5 mmol of (C2H5)(3)NBH3. Magnetic properties of these mixtures demonstrated soft magnetic phase characteristics. Relatively pure Nd2Fe14B nanoparticles with a coercivity of 5.09 kOe and magnetic energy product (BHmax) of 2.862 MGOe were obtained when (C2H5)(3)NBH3 initial content was 3.5 mmol. Exchange coupling nanoparticles of Nd2Fe14B, Fe3B and Fe2B were obtained with the coercivity of 3.787 kOe and (BH)(max) equal to 4.871 MGOe at (C2H5)(3)NBH3 content of 4.5 mmol. (C) 2018 Elsevier B.V. All rights reserved.