Preparation Of Ultrafine Spherical Liquid-phase Reduction Of Nickel Powder Method

Powders under1μm are called ultrafine powder in general. Ultrafine nickel powder has a great volume effect, surface effect and good electrical conductivity, so it was widely used in many application domains such as chemical energy materials, hard alloys, high temperature alloys, catalysts, electromagnetic shielding materials and aerospace domains. More and more researchers pay attention to it. A variety of preparation methods, such as gas phase method, solid phase method and liquid phase method, could be used when preparing ultrafine nickel powder. Owing to the advantages of convenient operation, high efficiency, good quality and appearance of products, reduction process of hydrazine has been adopted in this study. Under the condition of liquid phase, hydrazine hydrate(N2H4·H2O) was used as reductant, NiSO4·6H2O or NiCl2·6H2O as raw materials, defined amount of NaOH was added, different stirring ways were adopted in preparation of nickel powder. Properties of the powders were examined by characterization methods, such as scanning electron microscope (SEM), energy spectrum analysis (EDS), X-ray diffraction (XRD) and laser particle size analysis test.In this paper, the role of preparation process parameters such as reaction temperature, pH value, Ni2+ions concentration, N2H4-H2O/Ni2+mole ratio were discussed. Average particle size, morphology, dispersion, phase composition, reduction rate and time were easy influenced by those parameters. In order to acquire high purity ultrafine nickel powder with better surface morphology and smaller particle size under faster reaction rate and reduction rate, the better process parameters was obtained:Reaction temperature80℃, pH value of11, Ni2+ions concentration is0.5mol/L,[N2H4-H2O]:[Ni2+] is2-4. With the increase of temperature, reaction time required to shorten, reduction rate, the average particle size increase with the decrease of after first; Response should be under the condition of alkaline (pH>9), with the increase of pH value, reaction time required to shorten, reduction after rising first, average particle size increase with the decrease of after first, due to high pH reunion of nickel powder; With the increment of nickel ion concentration, reaction time required to reduce after the increase, reduction drop after first increases, the average particle size increases, high nickel ion concentration of nickel powder together; Dosage of reductant must be at least twice the nickel ion concentration, the reaction can more smoothly, with the increase of dosage of reducing agent, reaction time is reduced, the reduction rate increases, the average particle size is reduced, but high dosage of reducing agent due to reunion.The effect of stirring for reaction was discussed, found that, under the action of magnetic stirring, nickel powders were orientation arranged and coacervated; Under mechanical agitation, the particle morphology is neat, the spherical degree is high; Under the effect of ultrasonic, the reaction rate of nickel powder was speeded up, particle size was smaller and with good dispersion, but as a result of ultrasonic action, the morphology was not neat. What’s more, the effect of feeding mode on reaction was discussed, found that the mechanism and phenomenon of the reaction under different loading modes was different, different feeding way has certain influence on the experiment. The fastest reaction rate could be obtained when adding NiSO4solution to mixture of NaOH solution with hydrazine hydrate solution.