Preparation Of Ag-Pd Alloy Powders And Ag-SnO₂composite Materials

Electronic paste is an important raw material in the electronics industry, and its conductive phase performance plays a decisive role to the conductivity and density of the film. Silver-palladium alloy powders have excellent electrical, thermal and thermoelectric properties, and they are mainly used for the preparation of electronic paste.70Ag-30Pd electronic paste is the commonly used for MLCC. Electrical contact material is a crucial material for electrical switches, and its performance determines their contact reliability and breaking capacity. Silver-tin oxide composite material with good resistance to arc erosion, high resistance to fusion welding and lower contact resistance, is a kind of ideal new nontoxic electrical contact materials.In order to meet the requirements of the electronic paste, in this work, the submicron-sized silver-palladium alloy powders were prepared by Liquid Chemical Reduction Method with silver nitrate and palladium nitrate as the raw materials, and the effect of synthesis process on the morphology, size, and size distribution of the silver-palladium alloy powders were studied. Through the optimization of reaction processes, the preparation of Ag-SnO2electrical contact materials by chemical precipitation with tin tetrachloride and silver nitrate as raw materials was studied to improve the distribution of SnO2as a second phase in the Ag matrix. Scanning electronic microscope(SEM) was used to characterize the morphology of the powders and the composite materials, and the phases were analyzed by X-ray Diffraction.Nearly spherical silver-palladium composite powders with good dispersion and300～800nm in particle diameter were prepared by reducing silver nitrate/palladium nitrate with hydrazine hydrate using a symmetrical dripping method with arabic Gum as the dispersant. These powers were changed into Ag70-Pd30alloys with smooth surface by suitable heat treatment. The particle size is increased to0.5-1μm by the heated treatment.Completely alloyed and nearly spherical Ag70-Pd30alloy powders with good dispersion and300-500nm in particle diameter were prepared by reducing silver nitrate/palladium nitrate with ascorbic acid. Polyvinylpyrrolidone was used as the dispersant in the symmetrical dripping process. The particle size of these powders were further increased to0.5～1μm after the heated treatment.Sn(OH)4colloidal solution was prepared by the hydrolysis of SnCl4solution at60℃, and the Ag-Sn(OH)4composite powders were produced by reducing silver nitrate in the Sn(OH)4colloidal solution by ascorbic acid. The Ag-SnO2composite materials with a tin oxide mass fraction of12%were fabricated by hot pressing. The SnO2particles are smaller in size and more evenly distributed in the silver matrix compared with the Ag-SnO2composite material obtained by the mechanical mixing method.