The reaction mechanism of formation of chemically synthesized Nd2Fe14B hard magnetic nanoparticles

• Published in: Journal of solid state chemistry 2012-02, Vol.186, p.224-230
• Main Authors: Deheri, P.K., Shukla, S., Ramanujan, R.V.
• Format: Article
• Language: English
• Subjects: Chemical synthesis; Chemical synthesis methods; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Ferrous alloys; Heat treatment; Iron; Magnetic materials; Magnetic nanoparticles; Magnetic properties; Magnetic properties and materials; Magnetic properties of nanostructures; Materials science; Mechanism of formation; Methods of nanofabrication; Nanoparticles; Nanopowders; Nanoscale materials and structures: fabrication and characterization; Oxides; Physics; Reduction; Reduction–diffusion (R–D) method
• ISSN: 0022-4596; 1095-726X
• DOI: 10.1016/j.jssc.2011.11.022

Nd2Fe14B based magnetic materials exhibit excellent magnetic properties and are widely used in many engineering applications. However, chemical synthesis of this compound is challenging. In this work, the formation mechanism of chemically synthesized Nd2Fe14B magnetic nanoparticles was studied. Nd, Fe and B precursors were converted to Nd–Fe–B oxide by the sol–gel method, reduction of these oxides by CaH2 resulted in Nd2Fe14B nanoparticles. Nd2Fe14B phase formation resulted from two competing reactions: (a) Nd2Fe14B phase formation by direct combination of NdH2, Fe and B, (b) Nd2Fe17 phase formation from NdH2 and Fe, followed by Nd2Fe14B phase formation by the reaction of Nd2Fe17 and B. Addition of boron to Nd–Fe–B oxide during reduction resulted in improved magnetic properties. The activation energy for Nd2Fe14B phase formation was found to be 365kJmol−1. The optimum heat treatment temperature and time for Nd2Fe14B phase formation were found to be 800°C and 90min, respectively. The kinetics, reaction mechanism and morphology of Nd2Fe14B magnetic nanoparticles synthesized by sol–gel followed by reduction–diffusion at 800°C. [Display omitted] ► The formation mechanism of Nd2Fe14B magnetic nanoparticles was studied. ► Nd2Fe14B phase formation occurs by two parallel competing reactions. ► Reaction of NdH2, Fe and B resulted in Nd2Fe14B phase formation. ► Nd2Fe14B phase can also be formed by the reaction of Nd2Fe17 and B. ► Maximum wt% of Nd2Fe14B phase was obtained at 800°C and 90min annealing.