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 (C 2 H 5 ) 3 NBH 3 content. Nd-Fe-B intermediate phases were composed of small Fe 3 O 4 particles and Nd and Fe microcrystals encapsulated with nitriles . Fe 3 O 4 was reduced by BH 3 − into α-Fe as the (C 2 H 5 ) 3 NBH 3 content increased. After annealing, Nd-Fe-B oxide particles gradually agglomerated as the (C 2 H 5 ) 3 NBH 3 content increased, which affected the particle sizes after the reduction-diffusion step. Mixture of Nd 2 Fe 14 B and H 5 Nd 2 was obtained from precursors synthesized with 1.5 and 2.5 mmol of (C 2 H 5 ) 3 NBH 3 . Magnetic properties of these mixtures demonstrated soft magnetic phase characteristics. Relatively pure Nd 2 Fe 14 B nanoparticles with a coercivity of 5.09 kOe and magnetic energy product (BH max ) of 2.862 MGOe were obtained when (C 2 H 5 ) 3 NBH 3 initial content was 3.5 mmol. Exchange coupling nanoparticles of Nd 2 Fe 14 B, Fe 3 B and Fe 2 B were obtained with the coercivity of 3.787 kOe and (BH) max equal to 4.871 MGOe at (C 2 H 5 ) 3 NBH 3 content of 4.5 mmol.