Metal cobalt powder is a promising material added in steels for cutting tools, alkaline rechargeable batteries or heterogeneous catalysis and others for fabrication of abrasion strengthened composites. The final mechanical performance of composites is affected by the size of cobalt powder, which is closely dependent on the use of cobalt oxalate precursor. Developments of size controlled preparation methodologies are of great interest in materials chemistry. Previous works have revealed that the size of powders can be controlled through addition of some organic surfactants in preparation or by homogeneous precipitation methods. However, the former has a difficulty of separation and the latter has a shortcoming of low yield. In this study, the cobalt oxalate particles were prepared by precipitation using CoCl₂ and (NH₄)₂C₂O₄ solutions. Meanwhile a pulsed electromagnetic field (PEMF) was applied to the reaction system to improve the size of these particles. The effects of PEMF on the size of cobalt oxalate particles were investigated, and the mechanism model of interaction between PEMF and reaction system was established. The phase structures of products were characterized by X–ray powder diffraction (XRD). Packing density instrument and Laser Particle Size Analyzer were used to measure the sizes of obtained cobalt oxlte powders. Thermal decomposition was performed using TG–DSC thermogravimetric analyzer. The results indicate cobalt oxaldate ( β–CoC₂O₄·2H₂O) particles are formed of the packindensity of 0.393 g/cm³ and the average diameter of 3.5403 μm at PEMF voltage of 800 V. Compared with the paticles prepared without PEMF treatment, the packing density and average diameter decrease by 26.95% and 60.13%, respectively. The results of cobalt oxalate thermolysis show that products prepared from cobalt oxalate with and without PEMF both are β–Co particles. The average diameter of cobalt powders prepared from cobalt oxalate precursor with PEMF is decreased by 71.18% compared with that without PEMF.

This paper offers a simple and rapid separation technique for preparing lower cost cobalt powders, which would be susceptible for industrial application.