Study on nanometer ε-cobalt powder prepared by precipitation–hydrogen reduction in Co(II)–(NH4)2CO3–H2O system

Nanometer ε-cobalt powder was fabricated by liquid-phase deposition–hydrogen reduction method. Different precipitators were mixed with CoCl2 solution respectively to prepare the precursor of Co2(OH)2CO3 precipitation. Then the precipitation was washed, dried and hydrogen-reduced. Nanometer ε-cobalt powder was obtained. The characteristics of the precursor and cobalt powder from different precipitating agent were analyzed and compared. The precipitation mechanism of the Co-based precursor in Co(II)–(NH4)2CO3–H2O system was discussed and summarized for the first time. The results show that the use of (NH4)2CO3 as precipitating agent is conducive to preparing fine and uniform precursor and cobalt powder. Processing parameters of hydrogen reduction exert a great influence on particle size of cobalt powder: the lower reduction temperature, the finer the particle size, but the higher the oxygen content of cobalt powder. Close-packed hexagonal ε-Co powder with BET particle size less than 100 nm and oxygen content lower than 0.8 wt.% can be fabricated when reduction process was carried out at 400 °C. Moreover, the nanometer cobalt powders had spherical shape with good dispersibility.