The Influence Of Slurry Dispersed System And Metal Oxide Doping On The Properties Of ZnO Varistors

ZnO varistors have been widely used in power systems because of their unique IV characteristics.With the continuous development of power systems,the study of the varistors with high gradient and high energy absorption capabilities is so urgent.In this paper,A and B series ZnO varistors were prepared by changing the content of dispersant and the p H value of the slurry,and the effect of slurry dispersion on the performance of the varistors was studied.C and D series varistors were prepared by changing the the doping amounts of additive metal oxides Cr2O3 and Sb2O3,respectively.The effects of contents of Cr2O3 and Sb2O3 on the properties of the varistors were investigated.By changing the doping ratio and the sintering temperature of Cr2O3/SiO2,the highpotential gradient ZnO varistors were prepared.1.The slurry and the ZnO varistors were prepared with different contents of dispersant D-134 and different pH values.At relatively low D-134 content below 0.3 wt%,the viscosity remarkably decreased with increasing D-134 content.The dispersant on the surface of the powder had not yet reached the saturated adsorption capacity,which increased the possibility of adhesion between the oxide surfaces.The viscosity of the suspension was slightly increased with increasing D-134 content over 0.3wt%.The steric repulsion force was reduced and bridging was generated.The viscosity of the total slurry did not decreased with the p H value Increased,because the degree of hydroxyl ions adsorption on oxide particles as RCOO-'s partly replacement strengthened and other fully stretched free polymers went into the liquid phase,the slurry system only followed the electrostatic stabilization.The evenly distributed microstructure of the ZnO varistors are a direct result of the well dispersed slurry,which results in excellent electrical properties.2.ZnO varistors with different Cr2O3 contents were prepared.And the test results of the varistors show that the grain size of the ZnO varistors increases with the decrease of the Cr2O3 content.This is because the spinel content produced by Cr2O3 is reduced,and grain growth cannot be suppressed.C1 is based on formula,but there is a problem of large leakage and poor pressure ratio.On the basis of the C1 formulation,the Cr2O3 content is slightly reduced and the electrical performance is improved.When the Cr2O3 content is 0.2 mol% or 0 mol%,the electrical properties are best.C4 have potential gradient of 300.24V/mm,leakage current of 10?A,pressure ratio of 1.682,nonlinear coefficient of 20.65.C5 have potential gradient of 285V/mm,leakage current of 4.6?A,pressure ratio of 1.671,nonlinear coefficient of 23.17.3.ZnO varistors were prepared with different contents of Sb2O3.The test results show that the appropriate Sb2O3 content can inhibit the growth of ZnO grains because of the spinel content produced by Sb2O3 is increased.When the contents of Sb2O3 is 1.0 mol%,the ZnO varistors show excellent electrical properties,with the potential gradient of 233 V/mm,leakage current of 4?A,the voltage ratio of 1.721 and the nonlinear coefficient ? of 24.51.4.ZnO varistors were prepared with different ratio of Cr2O3/SiO2.The study shows that with the increase ratio of Cr2O3/SiO2,the content of Cr2O3 increases and the content of SiO2 decreases.However,the mole percentage of SiO2 in all metal oxides is more than that of Cr2O3,so the influence of the reduction of SiO2 is greater than that of the increase of Cr2O3.The grain size of the ZnO varistors increases with the increase of the ratio of Cr2O3/SiO2 because the spinel content produced by SiO2 is reduced,and grain growth cannot be suppressed.And with the increase of the ratio of Cr2O3/SiO2,the pinhole rate is reduced.When the ratio of Cr2O3/SiO2 is 0.59:2.13,the ZnO varistors show excellent electrical properties,with the potential gradient of 327.9 V/mm,leakage current of 0?A,the voltage ratio of 1.62,the nonlinear coefficient ? of 57.09 and the aging coefficient of 0.97.5.On the basis of E2,ZnO varistors with different sintering temperature were prepared.The Study shows that with the decrease of sintering temperature,the volatilization of the low-melting glass phase is reduced,resulting in decreased pinholes.However,as the sintering temperature continues to decrease,it is not beneficial to grain growth and sintering densification,and the pinhole rate is increased.When the sintering temperature is 1155?,the ZnO varistors show excellent electrical properties,with the potential gradient of 329.9V/mm,leakage current of 0?A,pressure ratio of 1.66,nonlinear coefficient of 65.1,the aging coefficient of 0.97,250 A 2ms square wave passing rate of 100%.It can be used for further study of ZnO varistors with highgradient and high energy absorption capabilities.