Sol-gel-based chemical synthesis of NdFeB hard magnetic nanoparticles

摘要

NdFeB nanoparticles were synthesized by a sol-gel method. Firstly, NdFeB gel was prepared by using citric acid and glycol as the gel, and the corresponding salts of Nd, Fe and boric acid. The gel was subsequently annealed under a high temperature condition to obtain NdFeB-oxide phases. Then NdFeB nanoparticles were yielded by reductive annealing of precursors. Microstructure, phase composition and magnetic properties were characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM) and vibrating sample magnetometer (VSM), and also differential scanning calorimetry (DSC) analysis was performed to determine the annealing temperature. At 400 degrees C, intermediate phases of Fe3BO5 and NdBO3 were formed and stable up to 600 degrees C; while at 800 degrees C, they would reacted in presence of oxygen to form NdFeO3 and B2O3. Nd2O3 and Fe2O3 were also formed at this temperature. SEM micrographs of reduced powders after washing process showed an average particle size below 100 nm in all the samples. VSM results showed the oxide powder formed at 800 degrees C had a coercivity of 1.55 kOe and a saturation magnetization of 1.08 emu/g. The powder synthesized by reduction of oxide powders at 800 degrees C had a coercivity of 1.02 kOe and a saturation magnetization of 14.17 emu/g.