Preparation And Properties Of The Ag-SnO₂ Electrical Contact Materials By Template Synthesis

As a new non-toxic silver based electrical contact material,Ag-SnO₂electrical contact materials have many excellent performance,such as anti-welding,arc erosion and abrasion resistance.They are widely used in low-voltage electrical apparatus.Because of the bad wettability between the second phase SnO₂ and Ag matrix,there are still some shortcomings in the preparation of Ag-SnO₂ electrical contact materials,such as poor material uniformity and uneven oxide dispersion.In order to solve the above problems,the preparation process of the template combined with the sol-gel method is used in this paper.The aim is to improve the dispersibility of SnO₂ particles in Ag and improve the comprehensive properties of the materials.In this study of the preparation of Ag-SnO₂ electrical contact materials,starch and filter paper were used as templates,and the sol-gel process was combined.The relevant important process parameters were set,and the principle of the experiment is explored.The effect of the process parameters on the performance of these materials was investigated by using the DSC and TG experiments,X ray diffraction,scanning electron microscopy and other testing equipment,tested the related physical properties of materials,such as resistivity,hardness and density.And the parameters of the processes included the effect of citric acid concentration,calcination process and the precursor mixing time on the properties of materials.The research content and main conclusions are as follows.（1）Starch and filter paper templates play an important role in the preparation process of Ag-SnO₂ electrical contact materials.The use of the template makes the Ag and SnO₂well-distributed dispersed,and the size of the powder is relatively uniform.Compared with the morphology of the powder made from the material without the addition of the template,the template of starch and filter paper can exert the space limitation of the template.The particle size of the prepared Ag-SnO₂ composite powder is between 5μm and 10μm.The oxide dispersion is better and the particle shape of the powder tends to uniform size of the spherical.The oxide and Ag matrix combine better.（2）The amount of citric acid has a great influence on the related physical properties of materials.The molar ratio(n（C₆H₈O₇）∶n(Ag⁺+Sn⁴⁺))3∶1 is better than other.The size of the Ag-SnO₂ composite powder is more small and uniform.The distribution of each element in the Ag-SnO₂ electrical contact materials is uniform,And the physical properties of the Ag-SnO₂ electrical contact materials,such as conductivity,hardness and density,are more excellent than others.（3）The experiment calcined in the air atmosphere,the calcination temperature at600℃,the effect of removing the impurities such as the template and gas can be improved.The surface of the material prepared by the starch template and the filter paper template has less oxide enrichment phenomenon,less porosity defects on the surface and the interior of the material,and has higher density of the material.（4）When the stirring time was 4 hours,the Ag-SnO₂ composite powder is smaller,and the distribution of SnO₂ particles in Ag matrix is more uniform.And there is no obvious agglomeration.The elements in Ag-SnO₂ electrical contact material are evenly distributed.The overall surface of the material is more smooth,less porosity defects,and the overall performance of the material is relatively good.（5）Through the optimization of the experimental process,the optimum preparation condition which contains the weight ratio of Ag to the oxide:88:12,using the citric acid as the reducing agent,the molar ratio(n（C₆H₈O₇）∶n(Ag⁺+Sn⁴⁺)):3∶1,stirring the precursor solution at 30℃for 4 hours,calcining the precursor gel in an air atmosphere,the calcination temperature:600℃,the holding time:2 hours.The physical properties of Ag-SnO₂ electric contact materials with no template such as conductivity,hardness,and density are 52.9%IACS,120.6 HV and 9.5085 g/cm³,and relative density of 96.18%.Using the starch template the physical properties such as conductivity,hardness,and density are 55.6%IACS,117.9 HV and 9.6099 g/cm³,and respectly density of 97.21%.Using filter paper template the physical properties such as conductivity,hardness,and density are 57.7%IACS,119.2 HV,9.6213 g/cm³,and relative density of 97.32%.