Two-Step Hydrometallurgical Preparation of Ultrafine Cobalt Powders

A two-step hydrometallurgical method was carried out to prepare ultrafine cobalt powders for the first time. The products were characterized by scanning electron microscopy coupled with energy-dispersive spectrometry, X-ray diffraction, laser particle size analyzer, and inductive coupled plasma. The cobalt powders contained the hcp-cobalt phase and fcc-cobalt phase. The proportion of hydrazine hydrate used in the two steps was found to be essential for the size of cobalt powders. As the proportion of hydrazine hydrate changed from 1:4 to 4:1, an obvious mean size evolution was observed from 1000 to 300 nm. A transition state {[Co(NH₃)₆](OH) }⁽ was proposed to explain the preparation process of ultrafine cobalt powders.