Research Of Preparing Silver Powders And Silver-copper Composite Powders With Liquid Phase Reduction Method

As a precious metal powder, ultrafine silver powder and silver series powder is widely used in light, electricity, magnetism, heat and catalysis areas. Silver powder and silver-copper composite powder is the basic functional materials used in electronic industry, the powder's quality and performance depends on its production process. In this paper, the preparation of ultrafine silver powders and silver-copper composite powders and the effects of various factors on the formation of them are studied, and the oxidation resistance and electrical properties of silver-copper composite powders are also tested and analysed.By adjusting the process factors, the controllable spherical high purity ultrafine silver powders that particle size is 0.5-2.0μm can be prepared with liquid phase reduction method. The effect of different reducing agents and surface protective agents on silver powders' morphology and particle size are tested. Using ascorbic acid (C6H8O6) and silver nitrate as raw materials, PVP as surface protection agents, we studied the effects of numerous process factors on silver powders'particle size and size distribution width, such as the reaction concentration, temperature, PH value, stirring rate and PVP dosage. Research results show that the particle size and size distribution width of silver powders increases as the concentration of C6H8O6 increases, and it decreases as PVP dosage and stirring rate increases; The particle size of silver powders increases first and then becomes smaller with the increase of AgNO3 concentration, and decreases with reduction temperature rises, however, the morphology of silver powders becomes irregular and the size distribution width of silver powders enlarges when temperature is above 60 degrees celsius. PH value is the important factor that impact the particle size and distribution of silver powders, in the range of 26.Silver-copper composite powders can be prepared with coprecipitation method, and it has oxidation resistance at room temperature. The silver-copper composite powders, which are prepared under the condition that the ratio of concentration of AgNO3 and CUSO4 is 1:1, having the morphology of mosaic-type massive particles. The silver-copper composite powders prepared under the condition of PVP dosage is 1.0[m(AgNO3)+m(CuSO4)] are well dispersed. The silver-copper composite powders, whose morphology is a large number of ultrafine silver particles embedded in the surface of copper particles, can be prepared when the concentration of C6H8O6 is 0.6mol/L. The particle size of silver-copper composite powders increases with the concentration of C6HgO6 increases; The particle size of silver-copper composite powders increases with the reduction temperature rises, and then decreases in small particle size range when the temperature continue rising; The particle size is influenced by PH value severely, and it first decreases and then increases with PH value increases.The silver-copper powders, of which the morphology is coated packing particles, can be prapared by adopted optimized process:T=70℃, PH=11, C(AgNO3):C(CuSO4)=1:1, the concentration of C6H8O6 is 0.6mol/L, and the oxidation temperature of the silver-copper powders comes to 285 degrees celsius,140 degrees celsius higher than pure copper powders, besides, the oxidation weight gain less, so it has good oxidation resistance; The volume resistivity of the conductive adhesive filled by the silver-copper composite powders, p(silver-copper powders)=1.26×10-3Ω·cm, which is significantly lower than the volume resistivity of copper powder-filled conductive adhesive p(copper powders)=3.52×10-3Ω·cm, close to the volume resistivity of silver powder-filled conductive adhesive p(silver powders)=8.45×10-4Ω·cm, hence, the silver-copper composite powders has good conductivity.