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Preparation and characterization of cobalt–bismuth nano- and micro-particles

Abstract An attempt at the preparation and characterization of Co – Bi nano- and micro-particles is presented. Firstly, predetermined compositions were obtained by simultaneous precipitation from solutions containing Bi(NO3)3 · 5 H2O and Co(NO3)3 · × H2O. The precipitates were heated under oxygen flow and in air, and thereafter reduced to metals under hydrogen flow at 673 K. Correlation between the predetermined and the actual compositions of the products was found. Characterization of the precipitates was carried out employing X-ray diffraction, scanning and transmission electron microscopy. The dimensions of the particles vary from nano- to micro- scale sizes. It was found that face centered cubic cobalt (i. e. fcc-Co modification, that is metastable up to 695 K) is the predominant cobalt phase while the hexagonal close packed cobalt (hcp-Co) is only present in small amounts. Thermodynamic calculations have shown that the molar specific surface energy of the fcc-Co should be around 0.5 J m−2 less than that of the hcp-Co (3.2 J m−2), in order to make the small fcc-Co particles more stable than those of hcp-Co.