Study On The Preparation Of Flake Silver Powders

Spherical or sphere-like were prepared by Liquid chemical reduction method, with hydrazine hydrate as reductant and PVP as surface-protection reagent. Flake silver powders with low loose density were also prepared by ball milling method, and a new type composite grinding aid agent was used in the experiments. SEM was used to characterize the morphology of silver powders, the structure was analyzed by XRD, the particle size distribution was analyzed by centrifugal sedimentation method, and the loose density was tested by hopper method. Influences of reaction temperature, concentration of AgNO3, adding time, agitating speed and surface protection reagent on the mean particle size of silver powders were studied in this paper. The optimum reaction condition was determined: reaction temperature is 20℃, concentration of AgNO3 is 0.35 mol/L, concentration of reductant is 2.1mol/L, adding time is 40min, agitating speed is 1000rpm, mole ratio of reductant to AgNO3 is 6 : l , and weight ratio of surface protection reagent to AgNO3 is 0.9. Under this condition, spherical or sphere-like, evenly distributed silver powders were generated. The experiment results indicated: the product particle size was influenced a lot by the reaction temperature, AgNO3 concentration, adding time, agitating speed and weight ratio of surface protection reagent to AgNO3. Among them the particle size increased with the increase of the AgNO3 concentration, but decreased with the increase of the reaction temperature and weight ratio of surface protection reagent to AgNO3. Considering the purity of the products, the optimum weight ratio of surface protection reagent to AgNO3 is 0.9. The XRD curves indicate that the ultimate product is cubic silver and crystallized well. Ball milling parameters were decided by orthogonal experiments. The factors of the ball gradation, ratio of ball to powder, rotational speed and milling time were analyzed with loose density and morphology of flake as check index. The composite grinding aid agent is much better than that of the single aid agent. The optimum usage of the composite grinding aid agent was 1.5%. The sequence of the factors was determined by orthogonal experiments: ball gradation, milling rotational speed, ball milling time, and ratio of ball to powder. The optimum ball milling parameters were determined: ball gradation is 1:2:4,rotational speed rate is 170rpm, ratio of ball to powder is 20:1 and milling time is 15h.