The Preparation And Properties Of A New Material-AgNiSnO₂

Silver Cadmium Oxide is considered as universal electrical contact for its excellent anti-arc properties.Current developental activities are focused on the innocuous and high performance contact materials to replace the hazardous substance AgCdO.So far,AgSnO₂ and AgNi are two kinds of contact materials and their electrical and mechanical properties are complementary to a certain extent.This paper is to research a new composite contact material--AgNiSnO₂.The former research is mainly about the electrical performance of contact material and is lack of the obligatory theory from material aspect.So the thesis in the beginning summarizes the relationship between the material factors and electrical performance.The material factors include matrix,second phase,additive and material defect.The first part also summarizes the concrete characteristics about the AgSnO₂ and AgNi materials.Secondly,since the AgNiSnO₂ material is prepared by Powder Metallurgy(PM),the sintering process such as the choice of molding pressure, sintering temperature,sintering atmosphere,sectionary sintering and electroless plating or not is particularly discussed.Thirdly,the particle size,surface morphology and content of nickel may influence the structure of materials after sintering and melting.The effect is investigated.Lastly,because the process of the sintering body prepared in the laboratory turing into the final contact material made in the factory is complicated and needs relatively long time,the thesis use the theoretical analysis to predict the conductivity and morphology of arc erosion after plastic fabrication.The whole experiments of sintering process indicate that the suitable deoxidation temperature of nickel is 350℃.In this temperature,NiO is completely deoxided and has least aggregated effect.The first molding pressure is 250MPa and the second is 500MPa.The first sintering temperature is 880℃and the second is 860℃.Under these parameters,the structure and properties of the AgNiSnO₂ are much fine.N₂ is chosen as the sintering atmosphere because if the atmosphere contains H₂,the SnO₂ will be disabled.Sectionary sintering can increase the density by 1%but not influences the structure.Coated powder AgSnO₂ can make the structure compact but not influences the density of the material.The morphology and particle size can influence the sintering and melting structure and properties.It indicates that the irregular morphology of nickel can hinder the first molding.The density including the "branch nickel" is smaller by 3.5%than the "smooth nickel".It is obvious that the material including small particle size nickel increases the first sintering effect but decreases the second molding effect.The irregular morphology of nickel tends to get together and produce the hole inside and around the cluster.SnO₂ distributes not only in the matrix but around the hole.The "Drum" appears on the surface of three samples after melting and the height of "drum" of the material including "smooth nickel" is the biggest.The size of "Ag-rich" area at the bottom of three samples are not big and the size of the material including "needle nickel" is smallest.The analysis of the phenomenon is that the morphology of "needle nickel" may hinder the liquid Ag's flow to the bottom and the small particle size may increase the "melting pool" viscosity.Furthermore,the content of nickel may influence the structure and properties of materials.It is investigated that when the content of nickel and SnO₂ is respectively 6%,the structure and properties of materials are excellent.Conductivities is an important parameter to the electrical properties for the contact material and the ability of anti-arc erosion determines the electrical life,so their research is valuable.Because the process of the final contact material made in the factory is complicated,it is significant to use the results got in the laboratory to predict the conductivity and morphology of arc erosion of final contact materials.The thesis uses the formulae got in the references and carries a series of theoretic analysis to predict the conductivity of the wire.The analysis shows that the the results calculated by the formulae is smaller by 4.5%-9.1%than the experimental results.For example,for AgSnO₂(6),the fitting conductivity of experimental results in laboratory is 2.01μΩ·cm and calculation result is 1.83μΩ·cm.The discrepancy is 9.0%,at 4.5%-9.1%,so it is thought that 2.01μΩ·cm is the experimental result for the wire material.After analyzing the different working environments between the melting and arc erosion and different structures before the melting and arc erosion experiment,it is thought that the size of "Ag-rich" area after arc erosion is smaller than the size after melting.Because the SnO₂ and nickel distribute more homogeneous and compact in wire structure and these particles have stronger ability to hinder the liquid Ag's flow to the bottom of the material.The effect of "Ag-SnO₂ layered" is equal for the structure between the sintering body and wire because this phenomenon is related to density discrepancy and wettability of materials not related to structure discrepancy.