Study On Electrodeposition Modified Ag/SnO₂ Electrical Contact Materials And Its Electrical Properties

Electrical contact materials and its components,whose performance directly affects the reliable operation and life of switching appliances,mainly play the role of on-off and load current.During the service process of Ag/CdO electrical contacts,there are serious environmental problems which limits its industrial application.For this reason,domestic and foreign scholars turn to the research and development of environmental-friendly silver-based electrical contact materials.As an alternative to Ag/CdO system,the eco-friendly Ag/SnO2 material has been successfully developed and put into the market at abroad.A great deal of research has been done on the development of Ag/SnO2 materials in China,but there are still some poor properties such as poor plasticity,high resistivity,short lif’e-time,contact resistance and so on.Based on the interface reaction principle,plasticity deformation theory and anti-arc erosion mechanism,one electroplating device with controllable rotation for preparing silver loaded SnO2 nanoparticles was designed in this paper.The Ag-loaded SnO2 composite powders(SnO2(e))with excellent interface bonding were synthesized,and its interface reaction mechanism was revealed.Ag/SnO2(e)electrical contacts were fabricated by hot extrusion processing,.Based on the interface mechanism between arc and material,the dynamic surface roughness,microstructure,contact resistance and arc erosion characteristics of Ag/SnO2(e)were investigated.1)A set of rotating electroplating apparatus suitable for preparing SnO2(e)composite powders was designed.Effects of c(AgNO3),plating time and voltage on the microstructure of SnO2(e)powders were investigated.The results showed that the optimum parameters for synthesis of SnO2(e)powders were:c(AgNO3)=0.01 mol/L,Te= 600 S,n= 120 r/min,Tbathing=60 ℃.Ve=10 V.The surface valence state of the Ag/SnO2(e)composite powder mainly exists in the form of+1 valence of Ag,+4 valence of SnO2,and non-stoichiometric ratio of SnO1.55.Compared with the TEM photograph of Ag/SnO2(t).a white transitional Ag layer exists on the TEM surface of Ag/SnO2(e)after surface electrodeposition,which effectively improves the interfacial bonding strength between SnO,and Ag.In this layer the crystal face index of Ag is(200),and its interplanar spacing d=2.04 A;and the SnO2 cr,ystal plane index is(200).and its interplanar spacing d=2.37A.2)Ag/SnO2(e)electrical contact composites,whose hardness,density and resistivity were analyzed,were prepared by high energy ball milling and hot extrusion.The tensile properties and microstructure of Ag/SnO2(e)were investigated.The optimal sintering process of Ag/SnO2(e)electrical contacts was as followed:Pm=900 MPa,Ts=900 ℃,t=6 h.Compared with traditional Ag/SnO2(Ag/SnO2(t)),the resistivity of annealed Ag/Sn02(e)was reduced to 2.2437 μΩ·cm,with hardness of 27.3 HV0.5 and density of 9.620 g/cm3.According to the tensile curve,the performance of annealed Ag/SnO2(e)material with diameter of 1.35 mm was obviously improved with the tensile strength at 299 MPa and the elongation at 10%.However,Ag/SnO2(t)electrical contacts can not be stretched due to the brittle fracture occurred directly.3)The relationship between normal pressure and contact resistance,arc erosion and dynamic surface roughness(Ra)of Ag/SnO2(t)and Ag/SnO2(e)were analyzed by means of contact meter and electrical life tester.With the change of the pressure,the contact resistance of all components showed a three-stage state,which firstly oscillates or decreases slowly,then decreases rapidly,and finally tends to stability.The pressure set at 60 N was more suitable and economical value during the electrical life testing.The smaller surface roughness,the smaller contact resistance under the same pressure.Compared with Ag/SnO2(e)material,the anode and cathode surfaces of Ag/SnO2(t)material have been eroded more seriously,stratified eroded surface,serious segregation,detachment and defects were observed.Meanwhile,the contact resistance distribution of Ag/SnO2(t)material was always larger than that of annealed Ag/SnO2(e)material,especially at the shorter testing time.This conclusion was in agreement with the variation law of the surface roughness.Similar failure modes such as "material transfer" and "droplet spatter" were observed from both Ag/SnO2(e)and Ag/SnO2(t)electrical contacts,but lower mass losses of the former were obtained.