Study On Preparation Technology Of High - Density Spherical Micron Silver Powder

As a new type of functional powder materials, silver powders are widely applied in chemical industry, energy, electronics, medicine, aviation, metallurgy and other fields. Previous studies have confirmed that the properties and application of silver powders depend mainly on a series of physical properties of silver powders, such as the particle size, particle size distribution, morphology, dispersion, density, structure and etc. Especially in some special industries, such as silicon solar cell industry, to obtain highly dispersed dense spherical micro-sized silver powders with a narrow size distribution, is of great significance for improving the performance of solar cell. Therefore, controlled synthesis study of micron silver powders has important significance in theory and implementation.In this paper, micron silver powders were studied as the main research object. Two different reductant systems for preparation process of monodisperse spherical micron silver powder was studied by liquid-phase reduction method. The obtained silver powders were characterized by laser scattering particle analyzer, scanning electron microscope, tapping apparatus, differential thermal analyzer and X-ray diffractometer, respectively.With ammonium ferrous sulfate as reductant, the effects of mixing way of reactant, molar ratio of reductant to silver nitrate (nFe:nAg), silver nitrate concentration, reaction temperature and the amount of tween65(TW65) on the particle size of silver powders were investigated. The results show that silver particles obtained under the reactant mixing way of silver nitrate solution quickly dumped into reductant solution have the smallest particle size and narrowest size distribution, particle size of silver powders decreases first and then increases with the increase of nFe:nAg, particle size of silver powders also decreases first and then increases with the increase of silver nitrate concentration, particle size of silver powders increases with the increase of reaction temperature, particle size, uniformity and density of silver powders becomes smaller and better respectively after adding tween65. Based on the single factor experiments, the preparation process of silver powders deoxidize by ammonium ferrous sulfate was optimized by the response surface method. After the optimize design, two mathematical regression models of between the average particle size (tap density) and factors were obtained, and the optimum process conditions were determined through the models. The optimum process conditions were:mass ratio of TW65/AgNO3,1%; silver nitrate concentration,0.5mol/L; dosage of deionized water,80mL; stirring rate,343rpm; molar ratio of nFe:nAg,6:1; reaction temperature, room temperature; mixing way of reactant, silver nitrate solution quickly dumped into reductant solution. The silver powders obtained under the optimum conditions were monodisperse and spherical particles with high purity, narrow size distribution, the average particle size of2.5μm, apparent density of2.183g/cm3and tap density of5.108g/cm3.With ascorbic acid as reductant, the effects of type of dispersant, the amount of arabic gum, adding way of dispersant, mixing way of reactant, silver nitrate concentration, ascorbic acid concentration, pH value of reaction and reaction temperature on the properties of silver powders were investigated. Based on the single factor experiments, the preparation process of silver powders deoxidize by ascorbic acid was optimized by the response surface method. After the optimize design, two mathematical regression models of between the average particle size (apparent density) and factors were obtained, and the optimum process conditions were determined through the models. The optimum process conditions were:mass ratio of arabic gum/AgNO3,1%; silver nitrate concentration,0.5mol/L; ascorbic acid concentration, lmol/L; pH value,2; reaction temperature,17℃; the adding way of dispersant, half of dispersant added into ascorbic acid and silver nitrate solution respectively; the mixing way of reactant, reductant solution quickly dumped into silver nitrate solution. The silver powders obtained under the optimum conditions were monodisperse and spherical particles with high purity, high yield rate, the size distribution of0.5-1.8μm, the average particle size of1.01μm, apparent density of1.912g/cm3and tap density of4.012g/cm3.