Silica Microspheres Silver Plating And Surface Preparation

Silver was a very important noble metal powder. And it is widely used in the conductive paste, conductive adhesive, antibacterial materials and other fields. In some special industries, such as the solar industry, to obtain high dispersive micron or sub-micron silver spherical was important to improve the performance of solar cells. The sub-micron spherical powder that coated silver on the surface, especially the coated relatively complete powders, could reduce the cost when instead of silver in certain circumstances. And the composite powders had the composite performance. So it was important to research electro less plating of silver on powders.In this paper, silica spheres as the substrate, coated silver on the surface of the microspheres by electroless silver plating, Main content of study was composed of preparation silica micro sphere and electroless plating of silver on silica micro spheres.To optimize the preparation of silica microspheres, the influence of some factors, such as the volume of ammonia, water, TEOS and ethanol on average particle diameter were discussed. The morphology, size and structure of silica microspheres were analyzed by scanning electron microscopy (SEM) laser particle analyzer and X-ray diffraction (XRD). The results show that the particle size of the silica microspheres increased with increasing amounts of ammonia. The particle diameter of microspheres would decrease when the amount of water increased. Increasing the concentration of TEOS could accelerate the hydrolysis reaction. Suitable temperature could help to keep the solubility of the ammonia in the solution, and the rates of nucleation and growth. Based on single factor experiment, the investigations of the interactive effects of average particle diameter (D50) was done using response surface methologoy. In the optimization, Design-Expert software was used to fit Central Composite Design (CCD) experimental data and quadratic regression model was developed for D50as response to the above parameters. Results showed that the optimal values of parameters of preparation of silica microspheres were as follows:ammonia6.5mL, water15mL, TEOS8mL and ethanol35mL.The D50were0.77μmby laser particle size analyzer and500-600nm by SEM.Silver-coated silica microspheres were prepared by electroless plating. A single factor analysis method was carried out to minimize the resistivity of silver-coated silica microspheres, by optimizing the reaction parameters such as the concentration of SnCl2, different added ways, the variety of reducer, concentration of main salt, etal. The results showed that the good coat of composite powder could be prepared, when the concentration of SnCl2was20g/L. Adding the ammoniacal silver solution with silica microspheres in it to the reducing agent solution, could obtain smaller resistance of silver-coated silica microspheres. The additives would ensure good dispersion, and reduce resistance of the powder. The suitable concentration of additive was2-3g/L.Based on single factor experiment, the investigations of the interactive effects of resistivity of composite powder was done using response surface methologoy. Results showed that the optimal values of preparation process of silver-coated silica microspheres by electro less plating were as follows:Loading of SiO2,3.5g; glucose,80g/L; Sodium tartrate,5g/L; Water,900mL/L; Ethanol,100mL/L; silver nitrate,25g/L; Amount of ammonia; Sodium hydroxide,2.5g/L; Water,1L;PVP,2-3g/L.The morphology, structure of composite powders was analyzed by XRD and SEM. Under optimal values, the crystallinity of silver coating was good and the surface of the composite powder was liked walnut-shaped. The electrical conductivity of composite powder was worse than the silver powder, but could be used with silver powder to enhance the conductivity. So it had a big gap to improve.