Preparation Of Zn₂SnO₄ Nanopowder And Its Application In Silver-based Electrical Contact Material

Silver-based electrical contact materials are the core components of electronic devices.Using inorganic metal oxides as reinforcing phases for silver-based electrical contact materials can significantly improve their properties such as hardness,anti-welding and anti-arc erosion and the like.Ag/SnO2 electrical contact materials,which are widely studied and applied,have problems such as higher contact resistance and excessive temperature rise during service,which affects the electrical life and reliability of electrical switches.Therefore,it is required to develop an enhanced phase which performed excellent in electrical and thermal conductivity to improve the performance of a silver-based conductive alloy.Zinc stannate(Zn2SnO4)is a wide bandgap n-type semiconductor material with higher thermodynamic stability and electron mobility.Zinc stannate has a high melting point and hardness,and the material system is eco-friendly and non-toxic,which can reduce the cost of the composite material.In this paper,cubic Zn2SnO4 reinforced phase nanopowders with anti-spinel structure were prepared by co-precipitation method and hydrothermal method.The Zn2SnO4 powder was modified by wet chemical method to prepare Ag-Zn2SnO4 composite powder and SnO2-Zn2SnO4 composite powder.Using Zn2SnO4 and SnO2-Zn2SnO4 powder as the reinforcing phase,the Ag/Zn2SnO4 and Ag/SnO2-Zn2SnO4 electrical contact materials were prepared by mechanical alloying and powder metallurgy,and the microstructure,electrical and mechanical properties were tested and characterized.Based on the process optimization datas of microstructure and sintering properties of zinc stannate powders,the temperature rise characteristics and electrical life properties of Ag/Zn2SnO4 electrical contact materials were characterized and the mechanism of their anti-arc erosion were analyzed.The main research contents and conclusions are as follows:(1)High purity cubic zinc stannate nanopowders were synthesized by chemical coprecipitation method and hydrothermal method.Using different zinc sources,tin source and precipitant as raw materials,zinc stannate nanopowders with spinel structure were synthesized.The effects of process parameters such as calcination temperature,zinc source type and precipitant type on the microstructure of Zn2SnO4 powder and the properties of Ag/Zn2SnO4 electrical contact materials were investigated.Using PVP as the surfactant,SnCl4·5H2O and ZnCl2 as raw materials,the Zn2SnO4 powders were synthesized by hydrothermal method,and effects of mineralizer types,PVP addition amounts and molecular weights of PVP on the preparation of Zn2SnO4 powder were investigated.Ag/Zn2SnO4 composite powders were prepared by in situ reduction.The SnO2-Zn2SnO4 composite powder was prepared by co-precipitation method,and the effects of calcination temperature and pH on the morphology and properties of the composite powder were investigated.The results show that the high-purity cubic Zn2SnO4 and Zn2SnO4 nanoparticles were synthesized by co-precipitation method.The powder morphology synthesized by hydrothermal method has flower-like structure,octahedron,cube,nanoparticle and the like.The purity and crystallinity of the Zn2SnO4 prepared by coprecipitation method is higher than that of hydrothermal method.The actual silver content of Ag/Zn2SnO4 composite powder is lower than the theoretical value,and the distribution of Ag and Zn2SnO4 particles is relatively uniform.(2)Ag/Zn2SnO4 electrical contact materials were prepared by powder metallurgy method.The microstructure,metallographic structure,electrical resistivity,hardness and density of the composites were investigated.By coprecipitation method,the optimal resistivity of Ag/Zn2SnO4 contact material can be reached at 2.31 ??·cm and meanwhile the corresponding density and Vickers hardness were 9.51 g/cm3 and 65.63 Hv0.5,respectively.The electrical conductivity of Ag/Zn2SnO4 electrical contact materials prepared by using Ag/Zn2SnO4 composites as the reinforcing phase is much better than that prepared by pure phase Zn2SnO4.The conductivity of the Ag/SnO2-Zn2SnO4 electrical contact material is slightly lower than Ag/Zn2SnO4 electrical contact material.Compared with the traditional Ag/SnO2 and Ag/ZnO electrical contact materials,Ag/Zn2SnO4 electrical contact materials have obvious advantages in electrical properties and density.The bonding state between the Ag and Zn2SnO4 phases could be well from the fracture structure analysis of Ag/Zn2SnO4 electrical contacts.(3)The electrical life testing of two different morphologies of Ag/Zn2SnO4 electrical contact materials was carried out by electrical life tester.The anti-arc erosion properties and its failure mechanism of Ag/Zn2SnO4 and Ag/SnO2 electrical contact materials were investigated.With the increasing current,the erosion of the Ag/Zn2SnO4(p)electrical contact material increases.The electrical lifetime of Ag/Zn2SnO4 electrical contact materials at 12A is about 20k operations,which is less than 50k times of Ag/SnO2 electrical contacts.The degree of arc erosion on the contact surface of Ag/Zn2SnO4 is also worse than that of Ag/SnO2 electrical contacts,But the advantage of the former is that the quality loss of the contacts is small.Some cracks and holes on the surface of Ag/Zn2SnO4(p)were observed.Especially,the arc-eroded surface of Ag/Zn2SnO4(p)has some phenomena such as nanowires,skeleton-like and flower-like structured particles,spherical cluster structure,droplets,Ag enrichment zone and Zn2SnO4 enrichment zone.The surface of Ag/Zn2SnO4(c)has ring-shaped pits and a network skeleton structure,and the distinction between silver and Zn2SnO4 enrichment regions is also obvious.On the whole,the arc erosion mechanism of Ag/Zn2SnO4 is mainly the droplet evaporation and sputtering of silver.The erosion morphology of Ag/Zn2SnO4(p)is better than that of Ag/Zn2SnO4(c).(4)Ag/Zn2SnO4 wire and electrical contact rivet products were prepared by hot extrusion processing combined with cold pressure welding.The temperature rise and electrical life properties of Ag/Zn2SnO4 rivet during actual working conditions were investigated.The temperature rise of Ag/Zn2SnO4 rivet is about 31K,which is lower than the required 65K,meeting the national standards.Under the condition of fusion welding,the surface of Ag/Zn2SnO4 rivet is seriously arc eroded.The corrosion pits,spherical agglomerates,fluffy Na-containing impurities,nanowire network structure and copper droplet particles on the arc-eroded surface were observed.