Microwave-Based Chemical Synthesis of Co-Alloyed Nd-Fe-B Hard Magnetic Powders

Modern high-energy-product permanent magnets derive their superior properties from nanoscale interactions, which are a sensitive function of the crystal size. Further property improvements require novel synthesis techniques to control the crystal size. Hence, we report a cost-effective and facile technique, i.e., microwave-based synthesis, to produce Co-alloyed Nd-Fe-B-based magnetic nanostructured powder. Dedicated microwave synthesis equipment with an optical pyrometer attachment was used to synthesize mixed metal oxides, followed by reduction diffusion to produce Nd-FeCo- B magnetic nanoparticles. Nanosized mixed oxide powders were formed in a single-step combustion after ignition, which was completed within a few seconds. In the reduction diffusion process, a two-step reaction was observed. Co and Fe oxides were first reduced to Fe and Co as the temperature reached 350 degrees C. Nd oxide was partially reduced to NdH2 at 350 degrees C and finally to Nd when the temperature reached 740 degrees C, when the desired Nd-2(Fe, Co)(14)B phase was also obtained. This reaction sequence matched thermodynamic calculations. Microwave power played a crucial role in controlling combustion temperature, crystal size, and coercivity of the Nd-2(Fe, Co)(14)B nanoparticles. The coercivity of these nanoparticles increased from 4.6 kOe to 8 kOe as the mean crystal size increased from 20 to 60 nm. The saturation magnetization was 106 emu/g.