Preparation Process And Mechanism Of Spherical Ultrafine/Nano Cobalt Powders

Spherical ultrafine/Nano cobalt powder is one of the key factors to the preparation of high performance nanocrystalline WC-Co carbide.In this thesis,Preparation process and mechanism of spherical ultrafine/Nano cobalt powders by hydrogen reduction of cobalt carbonate and calcium cobaltite were studied.Its major contents are as follows:Spherical ultraine cobalt powders prepared by hydrogen reduction of cobalt carbonate.1.The effects of pressure,surfactant and different solution system on the phase,morphology and particle diameter of CoCO₃ powder were studied during the preparation of CoCO₃.The results show that increasing the pressure is beneficial to the synthesis of CoCO₃,the average particle size of CoCO₃ powders decreases with increasing the content of surfactant?PVP?,while its morphology changed from irregular to square.Spherical CoCO3 powders were obtained in pure ethylene glycol solution.2.Ultrafine cobalt powder was obtained by hydrgen reduction using CoCO₃ as the precursors.The effects of reduction temperature and surfactant on particle size and morphology of cobalt powders were studied.The results show that the phases of cobalt powders were changed from?-Co to?-Co,the average particle size of cobalt powders decreases with increasing the content of surfactant,while its morphology tends to spherical.Precursor would be reduced to spherical cobalt powder with the mean particle size of 0.74?m after reduction at 700?for 2 h.Spherical Nano cobalt powders prepared by hydrogen reduction of calcium cobaltite.1.The effects of the ratio of CaO to CoO,the calcination temperature and the reduction temperature on particle size and morphology of cobalt powders were studied.The results show that the average particle size of cobalt powders decreases with increasing the weight ratio of CaO to CoO,but increases with the calcination temperature and reduction temperature.The spherical cobalt powders with the mean particle size of 84 nm are obtained when the weight ratio of CaO to CoO is 7:4 and the calcination temperature and reduction temperature are 1000?and 700?,respectively.2.The effects of refining mechanism of CaO cobalt powders during hydrogen reduction was studied.The results show that CaO regarded as the blocking agent can refine cobalt powders during the hydrogen reduction process.