Cobalt Metal Powder As Raw Material To The Preparation Of Cobalt Tetroxide New Technology

The cobalt oxide powder is usually prepared by thermal decomposing of cobalt oxalate precursors, and conventional process to product cobalt oxalate precursor is the liquid phase precipitation raction between solubled cobalt salts and oxalic acid or ammonium oxalate. The final performance of cobalt oxide is directly affected by the particle size and morphology of cobalt oxalate precursor. This paper proposes a new method which employs metal cobalt powder as materixal to prepare cobalt oxalate precursor. This method is based on the analysis of the standard free energy and influencing factors of the reaction. Cobalt oxide is finally prepared by thermal decomposition of the cobalt oxalate precursor.The powders prepared by the new method were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), laser particle size analyzer, thermogravimetrie-differential thermal analysis (TG/DTA).The results show that the needle-like cobalt powder was obtained by the solid-liquid reaction between metal cobalt powder and oxalic acid, and the diameter and length to diameter ratio of the needle-like cobalt oxalate powder can be controlled by changing reaction condition. The mass transfer of cobalt powder in the solid-liquid reaction can be described by the size unchanged shrinking core model, which find that the mass transfer process is controlled by chemical reaction, the activation energy is:Ea=26.335KJ/mol. The process parameters of needle-like cobalt oxalate prepared by cobalt powder and oxalic acid were studied. The results indicate that the length to diameter ratio of cobalt oxalate was closely related to reaction temperature, concentration of cobalt powder, stirring speed and so on. And the particle size and morphology of the product were also effected by whether adding nitric acid, hydrochloric acid and other inorganic acid or not. The length to diameter ratio of cobalt oxalate crystals will increase by adding a certain amount of nitric acid, and decrease by adding a certain amount of hydrochloric acid. Needle-like cobalt oxalate powder with an average diameter of 0.170μm and a length to diameter ratio of 46 was obtained under processing parameters followed:reaction temperature=50℃, n(H2C2O4):n(Co)=2.5:1, and the nitric acid concentration of 0.05 mol/LCO3O4 powder can be received by thermal decomposing of cobalt oxalate at a temperature higher than 287℃. Calcination temperature and holding time have a greatly effection on the formation of Co3O4 powder. When the temperature is 400℃or 600℃, calcination time is lh or 3h, the powder's morphology can be extended the cobalt oxalate precursor's. When the temperature is higher than 600℃or the holding time lasts more than 3h, the Co3O4 powder occurred serious sintering phenomenon.