| Thermodynamics of preparation of ultrafine nickel powders using polyol reduction was studied and plotted theφ-pH diagram of Ni-EG-H2O. The reaction path was predicted according to theφ-pH diagram. The effects of the factors on nickel powders morphology were systematically investigated. Infrared spectroscopy(IR), X-ray diffraction(XRD), scanning electron microscopy(SEM) and BET method were employed to identify the oxidation distribution and characterize the nickel powders of crystal phase, morphology and particle size.Preparation of ultrafine nickel powders from nickel hydroxide reduced by ethylene glycols was studied in this paper. It was shown that the reaction could complete within 4 hours. The particle size increased with prolonging the reaction time. Higher or lower water content of precursor decreased the reaction rate. PVP showed little effects on the reaction rate and the particle size. It could improve the sophericity of nickel powders shape and agglomeration. The concentration of NaOH increased the reaction rate and induced the nickel crystal to form hcp-nickel powders. The content of hcp-nickel powders was increased from 0.96% to 3.04% while concentration of NaOH changed from 10g/L to 60g/L. Compared with no-adding nucleation agent, the reaction rate was more quickly and powders with the particle size of 0.163μm were prepared when AgNO3 was added into reaction system. The optimum conditions were as follows: reaction time 4 hours, water content of precursor 60%, molar ratio of Ni(OH)2 to EG 0.02 and suitable PVP and NaOH. Spherical ultrafine nickel powders within 300nm of particle size were prepared.Preparation of ultrafine nickel powders from nickel oxalate reduced in ethylene glycols was studied. Compared with reaction of Ni(OH)2, the reaction of NiC2O4 could complete within 3 hours. Ni(OH)2 was reduced to cubic nickel powders and NiC2O4 was reduced to hexagonal nickel powders. The content of hexagonal nickel powders increased from 33.6% to 45.1% with the molar ratio of NiC2O4 to EG decreasing from 0.025 to 0.01. PVP could ameliorate the nickel powders shape and agglomeration by the chemical bonding between PVP and surface nickel atoms. The content of hexagonal nickel powders first decreased from 43.3% to 19.1%, and then it increased from 19.7% to 25.2% with increasing the concentration of NaOH. Nucleation agent of AgNO3 could accelerate the reaction rate and decrease the particle size. The content of hexagonal nickel powders decreases from 19.1% to 17.4% with adding nucleation agent. The content of hexagonal nickel powders about 45.1% could be obtained under the following conditions: reaction time 3 hours, molar ratio of NiC2O4 to EG 0.01, 5.0g/L PVP and 80.0g/L NaOH.The useness of EG was different in two systems of preparation. EG was reductant in the first system. It was either reductant or solvent in the second system.The oxidation products of ethylene glycol and oxalate ions in solution were identified by IR and XRD were CO32-. The result was in accord with the prediction of theφ-pH diagram.
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