Fundamental And Technological Study On Preparation Of Ultra-fine Ni&co-based Powders By Solution Spray Methods

Transition-metals ultra-fine Ni&Co-based powders, including sole metal oxide powder, elementary powder and alloy powder used as catalyst in artificial diamond industy, are series of important functional materials with special microstructures and properties. These materials are widely used in national defense and sophisticated military industry, as well as modern key industries like electronic information, green power, petrochemical industry and high-grade ceramics. Nowadays, most of the investigations are focused on the new preparation methods of varies ultra-fine powders. In this paper, we find out a new preparation method to produce powders with controlled microstructure refinement, homogeneous chemical composition and outstanding macroscopic properties. The method moreover, once been found out, can overcome the old ones'shortcomings and meet the high demands of variety fine powders with excellent properties, which has great theoretical value and practical significance.The new technology to prepare the Ni&Co-based ultra-fine powders via solution spray methods is proposed in this paper. The apparatus for solution spray processing is designed and built. Fundamental and technological studies of this solution spray technology are discussed systematically. The highlights can be summarized as follows:1) According to the characters of new solution spray processing technology we used, a set of experimental apparatus applied in preparing ultra-fine powder is designed and established. By using this set of device, many non-ferrous metal powder materials can be obtained and the materials can be utilized recycling in closed system.2) The thermodynamics of the NiO powder preparation process by solution spray methods is analyzed and discussed. The pure ultra-fine NiO powders are prepared successfully via solution spray process using the special experimental device established by ourselves. The effects of temperature, kinds of carrier gas, solution concentration, spray pressure and solution system of solution spray routes on the resulting composition, microstructure and morphology of NiO powder are investigated. The results show that a sole NiO fine powder can be obtained at the inert carrier gas (nitrogen) and oxidizing carrier gas (air, oxygen); the temperature has effect on both the morphology size and the conversion ratio of the raw materials; the solution concentration and spray pressure have effect on the resulting particle size and mophology; the hollow NiO microspheres are easily obtained when using nitrate as solute and the porous-microspheres NiO powder are obtain when using sulfate as solute; the high-density sub-micron NiO powder are obtain while chloride as solute, but its size does not meet with ODOP mechanism which is recognized widely at the solution spray to product ultra-fine powder process. When choosing the preparation conditions at the temperature of 800℃, the solution concentration of 1.0 mol·L-1, spray pressure 0.10 MPa while air as carrier gas and nickel chloride as the solute, the resulting pure ultra-fine NiO powder shows cube morphology, uniform particle size of about 0.4μm and the apparent density value of 0.63 g/cm3, which contains 77.1%nickel,0.08%chlorine.3) The thermodynamics of cobalt oxide powder preparation process by solution spray technology are discussed. A sequential transformation rules is adopted to cobalt oxidize at solution spray process, and the pure ultra-fine CoO and Co3O4 powder are prepared successfully via solution spray-oxidation process using the special experimental device established by ourselves. The effects of reaction temperature and kinds of carrier gas on resulting Co3O4 powder were investigated systematically, the results show that the reaction temperature has significant effect on the composition, structure, morphology of the as-obtain specimen, and crystallization degree of the product can be improved when using compress oxygen act as carrier gas. The high purity ultra-fine Co3O4 powder was obtain successfully at the temperature of 750℃, the solution concentration of 2.0 mol·L-1 and spray pressure of 0.25 MPa while air as carrier gas. It is found that spray pressure, gas-liquid ratio, solution concentration all have effect on the remaining chlorine content of the sample. Incomplete reaction, the adsorption behavior to hydrogen chloride of powder and the reverse reaction can result in the reduction of raw material conversion. The chlorine content of the product can be reduce when using gas-solid separation process to take insulation measures.It is found that the Co3O4 powder prepared by spray-oxidation method show good capacitive properties depict, of which the specific capacitance is about 103.5 F·g-1. When using ethanol as additional solvent or the urea as additional reactant, or the non-oxidized gas as the carrier gas, the CoO is easy to form by solution spray-oxidation method. The octahedron high pure ultra-fine CoO powder with well crystalline are prepared successfully under the temperature of 900℃, the cobalt chloride solution concentration of 0.5 mol·L-1, the spray pressure of 0.08 MPa, high pure nitrogen as carrier gas, solution with a small amount of ethanol.4) The reaction conditions effect on the resulting Co powder prepared by solution spray route without hydrogen reduced while chloride cobalt as raw materials is investigated carefully. It is found that high purity nitrogen as carrier gas is suitable; ethanol can be used as an effective reducing agent in the preparation process of Co powder. The amount of ethanol in solution, the reaction temperature, solution concentration and spray pressure have important impact on resulting Co powder properties. The pure FCC structure Co powder has been prepared successfully under the condition of high purity nitrogen as carrier gas, the temperature of 800℃, ethanol:water solution (1:1, V/V), solution concentration of 0.5 mol·L-1 and spray pressure of 0.08 MPa. The results of Zeta potential test show that the Co powders have better dispersion property and stability. It is also found that there exists a sequential transformation rules at cobalt oxide reduction process in the preparation process of cobalt powder.5) The preparation experiments of catalyst powder such as Ni7Co3, Fe7Ni3, FeNi3 and Ni7oMn25Co5 by solution spray route without hydrogen reduced are carried out. The results show that the catalyst powder (Ni7Co3, Fe7Ni3, FeNi3, Ni70Mn25Co5) with varieties morphology (silkworm-like, cockles-spheres, urchin-like, squama-like) has been prepared successfully by solution spray technique via control appropriate reaction conditions and the cation of solution in stoichiometric proportion.6) The dynamics theory of NiO and Co3O4 powder preparation processes by spray technology are discussed. It is found that three consecutive steps with different kinetics mechanisms control the whole preparation process of NiO and Co3O4. Thre are namely as:the solute crystallization, dehydration and decomposition of the solute, crystal growth of the product. By adopting Doyle equation and Coats-Redfern equation Joint Inference in solute dehydration and decomposition steps of the dynamic mechanism, we obtain the dynamic equation to the all small stage respectively. The dynamic equations of the NiO and Co3O4 grain growth rate are provided.