Control of morphology and structure for β-Co nanoparticles from cobalt oxalate and research on its phase-change mechanism

•Nanoscale precursor β-CoC2O4⋅2H2O can be prepared by mechanical solid phase reaction.•Growth mechanism, morphology and crystal structure of β-CoC2O4⋅2H2O have been studied.•Internal energy reserves of precursor making it directly generate β-Co in the thermal decomposition reaction.•Martensitic transformation of Co has been studied.•The Co powder will inherit the morphology of its precursor.

The face-centered cubic crystal structure β-Co has excellent performance. As the main material to produce high toughness hard alloys and metal cermet, its morphology and structure will have an important impact on the performance of the alloy. This study, based on solid-phase reaction, starting from the crystal structure studied, discussed the effection of the mechanical solid-phase chemical reactions on the morphology of the cobalt precursor structure, researched the cobalt phase change mechanism, and presented a method to prepare nano β-Co. With H2C2O4⋅2H2O and Co(NO3)2·6H2O as raw materials, nano-crystalline cobalt oxalate powders with nearly spherical shape have been prepared by using solid-phase chemical reactions in high-speed ball milling, and then by decomposing at 400–450 °C, the target was prepared. The thermodynamical and IR analysis has been studied. The microstructure of the powders was characterized by XRD, SEM, TEM. It has been identified that a spherical, fcc structure, 100 nm β-Co powders was synthesized successfully, which confirmed the theoretical feasibility of this study.