Design And Preparation Of ZTO/Ag Electrical Contact Materials

In low-voltage contactors,MeO/Ag electrical contacts have a wide range of applications.CdO/Ag has excellent performance,but cadmium pollution problem limits its application;SnO₂ is most likely to replace CdO,but its poor wettability with Ag,resulting in serious contact heating,deterioration of contact characteristics and other issues Therefore,SnO₂ is compound-modified,and the formed tin-zinc ternary oxide ZTO?Zinc Tin Oxide?has a complex crystal structure,good conductivity,good wetting and bonding strength with metals,and can ensure that Ag-based electrical contact materials have stable electrical contact characteristics during arc erosion.Therefore,this article designs zinc tin oxide as the ZTO/Ag electrical contact material formed by the second phase,and uses first-principles method to study the ZTO/Ag interface structure and bonding mechanism.On this basis,ZTO/Ag electrical contacts were prepared by powder metallurgy,and the effects of ZTO on the structure and resistance to arc erosion of Ag-based electrical contacts were discussed.First-principles calculations were used to study the interface binding characteristics of Zn₂SnO₄/Ag.The recombination of Zn₂SnO₄?111?surface and Ag?111?surface can form a stable interface structure,and Wsep?4.04 J/m²?higher than that of SnO₂/Ag?2.83 J/m²?and common binary Oxide/Ag?0.7-3.5 J/m²?,showing a stronger interface bonding strength.The calculation results of bond length show that 11 groups of Ag-O bonds are formed at the interface of Zn₂SnO₄?111?/Ag?111?,and Ag-O bonds form a stable tetrahedral structure;density of states and charge density calculation reveals the Zn₂SnO₄/Ag interface bonding mechanism is that charge transfer occurs between Ag-O at the interface and is shared by Ag and O atoms.The formed Ag-O bond has covalent-ionic bond characteristics,so the Zn₂SnO₄/Ag interface exhibits higher interface bonding strength.The chemical co-precipitation method and solid-phase sintering method were used to realize the controlled synthesis of ZTO,including Zn₂SnO₄,ZnSnO₃,and SnO₂.Using the precipitation method to obtain precursors of Zn₂SnO₄,including Zn4?OH?6CO₃ and SnO₂·x H2 O.When the sintering temperature rises from 900 ? to 950 ?,the conversion rate of zinc stannate is significantly increased from 40% to 83%.Zn₂SnO₄ particles are uniform and have a size of 50-200 nm.Zn₂SnO₄ powder with a size of 100 nm was obtained by ball milling-solid phase sintering?1000?,4 h?.In addition,the co-precipitation method is used to obtain: spherical ZnSnO₃ powder particles with a size of 100-200 nm;lamellar SnO₂ powder with a size of 0.2-1 ?m.The densification process of ZTO/Ag electrical contacts was studied and the best preparation process was determined.After mixing powder?200 r/min ball milling,4 h?and pressing?200 MPa?-sintering?860?,2h?,samples with connected pores??= 75-80%?were obtained.The subsequent densification process adopts the re-pressing method and hot extrusion method.When the re-pressing pressure is 1200 MPa,the re-sintering temperature is 840? and the sintering time is 2 h,the relative density of the Zn₂SnO₄/Ag electrical contacts reaches more than 97.1%;the relative density prepared by hot extrusion method reached 96.7%.ZTO/Ag electrical contacts with a content of 2-15wt% were prepared,and ZnSnO₃ may decompose during this process,while the composition of Zn₂SnO₄ is stable.The second phase can be evenly distributed in the silver matrix without obvious pores.After hot extrusion-cold rolling,the hardness of the electrical contacts reached a maximum of 79.3 HV,and annealing resulted in a decrease in hardness,and there was a certain positive correlation between the hardness and the density of the electrical contacts.In the arc erosion experiment,compared with commercial SnO₂/Ag electrical contacts,the preparation of Zn₂SnO₄/Ag electrical contacts in this paper has more advantages,proving the good wettability between Zn₂SnO₄ and silver.