Preparation Of ZnO Varistor Ceramics And Study On Its Surge Current Withstanding Capacity

ZnO varistor ceramics are widely used in circuit systems in the fields of military,communications,power transmission,and consumer electronics,due to its unique nonlinear electrical effects and.Up to now,how to improve the surge current withstanding capability of varistor is an urgent problem for domestic researchers since many varistors with high surge current withstanding capability still need to be imported from abroad and the application cost of domestic varistor is very high.Therefore,it is of great research significance to improve the surge current withstanding capability of the varistor while taking into account the varistor properties.In this thesis,firstly,we prepared ZnO varistor ceramics by traditional solid phase method,and studied the effects of sintering temperature,Mn content and incorporation form,and BaTiO₃ doping on the structure and properties of the samples;and then,we prepared ZnO varistor ceramics by microwave solid phase method,and further investigated the microwave sintering process by orthogonal experiment,in addition,the effects of Bi₂O₃ content and BaTiO₃ doping on the structure and properties of the samples.The specific results are as follows:In the study of traditional sintering,With the increase of sintering temperature,the grain size of the sample increases and the electric field of the sample decreases.When the sintering temperature is too high,the sample performance deteriorates due to the amount of Bi₂O₃volatilization increases.With the increase of Mn content,the nonlinear coefficient increases and the leakage current decreases,while the density and structural uniformity of the ceramic decrease when Mn is overdoped.The performance of the sample is much better when Mn is incorporated in the form of MnO.The Ti introduced by BaTiO₃ can increase the grain boundary potential barrier.On the other hand,a thermally stable BaSb₂O₆ phase is formed in the ceramic when incorporating BaTiO₃,in which Sb element with the valence state of+5 can limit the migration of O^2-and effectively improve the surge current withstanding capability of the sample.For traditional sintering method,we prepared the ZnO ceramics at a sintering temperature of 1150℃,in which the doping amount of MnO and BaTiO₃ is 0.6 mol%and 1mol%respectively,with varistor electric field of 532.07 V/mm,the nonlinear coefficient and leakage current density are 56.20 and 1.44μA/cm²,respectively.Under the pulse current with peak current of 520A,residual voltage ratio of 2.6,and the varistor voltage change rate of 6.5%after impact.In comparison,the properties of microwave sintered ZnO ceramics doped with 0.7mol%Bi₂O₃are much better.During the sintering process,the sintering temperature is 1100℃with a heating rate of 7℃/min,and the holding time is 1.5 h.The overall performance of microwave sintered ZnO ceramics was further improved by doping 1 mol%BaTiO₃,for which the density was 5.596 g/cm³,the electric field was 430.5 V/mm,the nonlinear coefficient was 68.31,the leakage current density was 0.86μA/cm²,Under the pulse current with peak current of 880A,the residual voltage ratio of the sample is 2.4,and the varistor voltage change rate after impact is 4.8%.The electrical properties of ZnO varistor is effectively improved by BaTiO₃ doping and microwave sintering,which provide new ideas for preparing high performance varistor ceramics.