Nd-Fe-B particles with reduced oxygen content and enhanced magnetic properties prepared through reduction-diffusion and novel washing process

The Nd-Fe-B particles with high (BH)max were obtained through a wet chemical method involving reduc-tion-diffusion (RD) and heptane ball milling. The phase purity, microstructure, and magnetic properties of the magnetic particles produced by RD can be affected by the washing process used. In this study, various washing processes, including wet ball milling (WBM) washing with ethanol or heptane and conventional washing with deionized water (DIW) were explored. The WBM washing method involves the low energy ball milling of RD powder in ethanol or heptane instead of several repetitions of water washing steps. This results in the production of Nd-Fe-B particles that exhibit enhanced morphology, phase purity, and magnetic properties when compared to those obtained through the standard DIW process. This is likely due to crushing agglomerates formed during the RD into uniform sized particles and efficient removal of by-products such as Calcium oxide and residual Calcium. In addition, WBM washing in heptane showed high magnetic properties, including a coercivity of 3.9 kOe, remanence of 135 emu/g, and magnetic energy density of 16.7 MGOe. This is thought to be due to the minimal oxidation of Nd-Fe-B particles and absence of an amorphous layer on the surface of the particles. The findings of this study could be useful to produce other high-performance magnetic particles using RD process.