Silver Tin Oxide Composites

The development, qualities, applications and technics of the contact materials was reviewed in this paper and the development trends of contact material and the problems for all kinds of it to be solved are present as well. As the substitute of AgCdO, Ag/SnO₂ is the studying hotspot of contact materials and it should have broader foreground in application.With AgNO₃ and Na₂SnO₃ as raw materials ,citric acid, oxalic acid and sulfurous acid as reducing agents, different morphological silver tin oxide contact materials with different granularity SnO₂ and different density Ag/SnO₂ was synthesized by controlling the hydrothermal and post treatment conditions. The hydrothermal conditions were chosen based on the analysis of the form and electrode voltage of citric acid and oxalic acid in the water.The results show that irregular Ag/SnO₂ powder has been synthesized when citric acid was used as the reducing agent. Round Ag/SnO₂ powder was fabricated while oxalic acid was used as the reducing agent. Flake Ag/SnO₂ powder was fabricated when with sulfurous acid as the reducing agent. The particles of the resultant Ag/SnO₂ powder were very small and SnO₂ couldn't be observed on the surface of the samples by SEM. The characteristic peaks of SnO₂ were indistinctness in the XRD. EDX analysis shows that SnO₂ is dispersed homogeneously in the Ag base, Ag and SnO₂ had the possibility of bond.The theoretic calculation shows that Sn⁴+ is precipitated completely when the pH values of the solution ranges from 2 to 9. The loss of C₂O₄²-is the least when pH>6 with oxalic acid as the reducing agent and the pH value should keep above 9.8 when the sulfurous acid was used as the reducing agent.For the aftertreatment of Ag/SnO₂, the tabletting time, sintering time and the sintering temperature influence the density of Ag/SnO₂ distinctly.The optimal post treatment conditions are as follows: tabletting time 8 minutes, sintering time 3h, sintering temperature 750°C The metallographic examinations show that SnC>2 with very small particle size was dispersed homogeneously in the Ag matrix and the performances of Ag/SnO2 powders synthesized by the hydrothermal method should be better than those synthesized by powder metallurgical methods and other methods based on the optimization design principle. The growth of the SnO2 crystal is abnormal in the sintering process, but in the 110 plane. And with the rising of temperature, SnO2 will be crumped up; At the same time the SnO2 can repress the grain of Ag to grow up. both them squeezing mutually, insetting mutually, making their interface combine batter, the smooth wet strengthen. Then it can repress the segregation of SnO2 which is the great problem of Ag/SnO2 synthesized by powder metallurgical methods. SnO2 in the product synthesized by powder metallrugy method and reaction compound method is aggregated seriously when its content reach 10%. While the SnO2 was not aggregated when its content reached 16% in the Ag/SnO2 which was synthesized by this method. It may reduce the cost by raising the content of SnO2 but not to affect the function by using a hydrothermal method.