|
Uses of ultrafine powders are closely related to the properties, and the properties, to a large extent, depend on their shapes and particle sizes. As a key material of micro-electronics industry, there are special requirements for the shape of ultra-fine silver powder. At present, Silver powders used are mostly of spherical morphology, which need to be milled into silver flake to improve their conductivity. Fibre silver powders can form conductive circuit nets, which improved the conductive properties effectively. A variety of ultra-fine metal powder materials with fibre morphology have been prepared by our research group, by coordination precipitation-thermal decomposition method. Based on these achievements, coordination precipitation-thermal decomposition method was employed to study the preparation of fibre silver powders by the writer.According to the law of conservation of mass and law of simultaneous equilibrium, the thermodynamic equilibrium mathematics model of Ag(Ⅰ)-C2O42--NH3-NH4+-H2O system is established, and the corresponding logarithms concentration of metal ions-pH value is also drawn firstly in this paper. Based on these diagrams, the range of pH value in the coordination precipitation process was determined. After physical and chemical conditions of solution’s effect on the morphology of precursor was researched, systematically, by the experiments. The optimized process conditions of preparing rod precursor were confirmed as:two-step reverse-feeding way of deposition agent, reaction temperature 60°, Ag+ concentration 0.4mol/L, pH value of 3.8 to 4.8, charging 30min, assembly time 30min, stirring rate 600r/min, PVP amount of m(PVP)/m(AgNO3)=0.1.The feasibility of silver obtained directly from oxalate silver salt by thermal decomposition and the stability of silver under the conditions of thermal decomposition were analyzed in this paper also, from thermal dynamic point of view. In addition, the effects of the precursor morphology, thermal decomposition temperature, thermal decomposition time and atmosphere on the final products were studied systematically also. The results showed that:in the VN2:VCO2=3:1 atmosphere, thermal decomposition temperature of 140℃, heating for 0.5h and time of heating preservation 2.5h, fine silver rod with specific surface area of 1.054m2/g, can be prepared with a good dispersion.
|