Research On The Preparation Of Ultrafine Nickel Powder By Chemical Vapor Deposition

With its excellent electrical, magnetic, catalytic and mechanical properties, ultrafine nickel powder is widely used in these fields such as catalyst, battery material, electrode of multi-layer ceramic capacitor, powder metallurgy and so on.In this study, the experimental conditions of synthesis ultrafine nickel powder by chemical vapor deposition were investigated. We not only designed but also improved the preparation apparatus, by which the ultralfine nickel powder could be prepared successively. The effects of carrier gas (N₂) flow, H₂ concentration, reaction temperature, H₂ flow rate, reactor structure and precursor (NiCl₂) evaporation temperature on the products were analyzed systematically through the experiment of single factor condition. The particle size, structure and morphology of the products were characterized by x-ray diffraction (XRD), scanning electron microscope (SEM), particle size analysis. We obtained the optimum experimental conditions through the optimization of process parameters. The results indicated that after the first-stage dehydrating for four hours under 135℃, NiCl₂·6H₂O was grinded, followed by the second-stage dehydrating for two hours under 250℃, and then six crystal water could be removed completely. The main influencing factors of powder morphology and particle size are carrier gas flow, H₂ concentration, reaction temperature, H₂ flow rate, reactor structure and precursor evaporation temperature, while the crystallinity mainly related to carrier gas flow rate, reaction temperature, reactor structure. When NiCl₂ evaporation temperature was 900℃, H₂ flow was 9.6 L/ h, carrier gas flow was 50 L/ h, H₂ concentration was 20%, reaction temperature was 1100℃, the nickel powder prepared in the reactor without space-limiting component was washed for five times with water and three times with ethanol, and deposited for two minutes in the soultion of ethanol to remove large particles, then the desirable powder, which has high purity, high crystallinity, small partical size (with 0.31μm average partical size), narrow particle size distribution, spherical or similar spherical morphology , could be obtained. Its specific surface area is 1.98 m²/g, oxygen content is 0.33%.The nickel powder prepared by chemical vapor deposition are of such excellent advantages as high purity, large specific surface area, high crystallinity, uniform and tunable particle size distribution, therefore, this method in the preparation of ultrafine nickel powder has wide application prospect in industry.