Preparation And Properties Of Ag/SnO₂ （One-Dimensional Morphology）Electrical Contact Materials

Ag/SnO₂ composites are the most widely used electrical contact materials because of their excellent wear resistance,anti-welding,anti-arc erosion properties and non-toxicity.However,the uneven distribution of SnO₂ in Ag matrix and the poor wettability will increase contact resistance,temperature-rise,and the difficulty of processing.So this experiment mainly research on SnO₂ phase of different one-dimensional morphology to improve the distribution of SnO₂ in silver matrix,aiming to improve the comprehensive performance of Ag/SnO₂ electrical contact materials.The main work and conclusions are as follows:SnC₂O₄ precursors with different morphology,including sheets,short rods,long rods,bundles and needles,were prepared by chemical precipitation,changing experimental parameters,such as reactant types,reaction temperature,reactant concentration,additive and titration rate.After calcined at 600℃ for 1h,SnC₂O₄ precursors with different morphology were thermally decoposed into SnO₂ powder,keeping their original morphology all the same.And the aspect ratio of needlelike SnO₂ could reach 50:1.The Ag/SnO₂ composite powder was prepared by the non-uniform precipitation method on the basis,and then electrical contact materials with SnO₂ homogeneously dispersed were prepared by hot-pressing sintering.Subsequently,the reslut showed that the comprehensive properties（hardness,conductivity,breakdown strength）of electrical contact materials reinforced by needlelike SnO₂（89.98 HV,65.48%IACS,2.71×106 V·m-1）were superior to those reinforced by short rod-like（85.95 HV,53.98%IACS,2.27×106 V·m-1）,long rod-like（88.77 HV,56.72%IACS,2.54×106 V·m-1）and bundled（66.14 HV,58.07%IACS,2.84×106 V·m-1）SnO₂.The heat treatment temperature of SnO₂ had important influence on material properties.The composite materials prepared by needlelike SnO₂ calcined at 600℃ showed the highest relative density（98.79%）,hardness（89.98 HV）and electrical conductivity（65.48%IACS）.When improving the heat treatment temperature to 700℃,the breakdown strength of composite materials could be further improved,which was beneficial to improve the anti-arc erosion resistance.But the electrical conductivity（57.86%IACS）was simultaneously slightly decreased.The interfacial area between Ag and SnO₂ could be increased by increasing the mass fraction of needlelike SnO₂,increasing the strength and hardness in the Ag-based electrical contact materials.But due to increasement of the hole numbers and enhancement of dislocation scattering effect,the conductivity was significantly reduced.Considering that,electrical contact materials reinforced by needlelike SnO₂ of 12%mass fraction had the excellent anti-arc erosion resistance,the appropriate hardness（89.98 HV）and the high conductivity（65.48%IACS）,which was superior to requirements of the national standard for sheet products（hardness ≥80 HV,conductivity ≥57.5%IACS）.