Synthesis Of Micron-sized Spherical Silver Particles For Conductive-paste

In this paper, Liquid Chemical Reduction Method was used to prepare micron-sized spherical silver particles used for conductive paste.In the experiment, it’s studied that the influences of reactant, pH value of solution, the way and the speed rate of mixing, the species and the concentration of the disperser, the concentration of the reactants, on the morphology and the particle size of silver powders. The growth processing of the silver powders was also discussed in the work. The products’ chemical compositions was detected by EDS, the morphology was observed by SEM, the structure was characterized by XRD, the particle size was analyzed by microscopic method or laser light scattering, and the loose density and the tap density were tested according to the Chinese Standard in point. Finally, micron-sized, sphere-like silver powders used for conductive pastes were prepared by optimizing the technological conditions.The experiment results indicated:it is easier to get high-purity, well dispersed, micron-sized or sub-micron-sized, sphere-like silver powders with ascorbic acid as reducer than hydrazine hydrate or formaldehyde. Ascorbic acid being reducer, the morphology and the size of the silver particles were influenced a lot by the pH value of the solution. As the pH increases, the sphere shape of the silver particles gets better, the surface gets rougher, and the mean particle size reduces. About pH=2～4, there is a key change of the morphology and the growth mechanism of silver powders. The pH less than the point, silver particles grows up depends mainly on the crystallization; and the final particles appears regular polyhedron, and even flaky, caky, like branches and leaves; and the surface is relatively smooth, the density is relatively high. The pH greater than the point, silver particles grows up depends mainly on the coalescence; and the final particles appears spherical; and the surface is relatively rough, the density is relatively low. In addition, the way and the speed rate of mixing, the species and the concentration of the disperser, and the concentration of the reactants, have different effects on the morphology and the size of silver powders. The optimum technological conditions was as follows:reducing silver nitrate by ascorbic acid, silver nitrate concentration of0.083～0.3532mol/L, mole ratio of reducer to oxidant of2-0.58:1, pH value of the solution of1.0～1.5, gum Arabic as dispersant, mass ratio of gum Arabic to silver nitrate of0.053:1, mixing through symmetrically dropping for30--40min.The silver powders prepared at the optimum technology can meet the prosperity requirements of conductive paste. The yield was98.88%～99.18%. The products was high-purity, sphere-like, surface-smooth, well dispersed, and the mean particle size was1.16～1.19μm, the loose density was2.0～2.1g/cm3, the tap density was4.0～4.3g/cm3. Expanding test proved that the process was stable enough to be used for expanded production.