Influence Of Oxide And ZBS Glass On The Structure And Performance Of ZnO Linear Resistances

ZnO linear resistor is a kind of semiconductor ceramic material,which is developed on the basis of ZnO varistor.Compared with the traditional metal and carbon materials,ZnO linear resistor has some advantages,such as small nonlinear coefficient,small resistance temperature coefficient and high energy absorption density,and so on.So it is widely used in braking resistors and circuit breakers.In recent years,the research of ZnO linear resistance is mainly focused on the preparation process and oxide doping,etc.Through related research,the performance of ZnO linear resistance has been improved,such as linearity and resistance temperature.However,there are few studies on the effect mechanism of different oxides on the performance of ZnO linear resistance.Moreover,little research has been reported on the glass-doped ZnO linear resistance.In this thesis,ZnO linear resistance was prepared through the solid-phase sintering method,and the base formulation was ZnO:Al₂O₃:MgO:Ti O₂:Y₂O₃=86.684:7:5:0.6:0.716（wt.%）.To obtained the optimal preparation process,the paper firstly investigated the effects of different raw material pre-sintering methods（No pre-sintering,pre-sintering raw materials except ZnO（MATY）and pre-sintering all raw materials（ZMATY））,electrodes（Ag and Al）and sintering temperatures on the structure and properties of ZnO linear resistors.Then,the effects of different additives（La₂O₃,Si O₂ and ZBS glass（molar ratio ZnO:B₂O₃:Si O₂=6:3:1））on the structure and properties of ZnO linear resistors were investigated,and the mechanism of action was revealed.The main conclusions are as follows:（1）Pre-sintering the raw material except ZnO（MATY）can improve the densities and temperature resistance performance of the samples.Applying aluminum electrode to ZnO linear resistance can obtain smaller resistance value,higher linearity and temperature resistance performance.When the sintering temperature is 1360℃,the distribution of grain size of the ZnO linear resistance was uniform,and the linearity and temperature resistance performance of the samples is the best.The best preparation process was determined as follows:pre-firing MATY,using aluminum electrode which can form ohmic contact with ZnO,and sintering temperature of 1360℃.Under this preparation process,the bulk density and relative density of ZnO linear resistance are 5.017 g/cm~3 and 94.83%,respectively,with a resistivity of 103.60Ω·cm,a nonlinear coefficient of 1.05,and a resistance temperature coefficient of-1.28×10^-3/°C.（2）La₂O₃ mainly reacts with oxides other than ZnO to produce lanthanum-rich phase,which improves the temperature resistance performance,but also adversely affects the linearity of the ZnO linear resistance.When the amount of La₂O₃ doping is 0.5 wt.%,the ZnO linear resistance has the best overall performance,with a bulk density of 5.026 g/cm~3,a resistivity of 104.89Ω·cm,a resistance temperature coefficient of 0.21×10^-3/°C and a nonlinear coefficient of 1.06.When the addition of Si O₂ is small,it mainly reacts with MgO and Al₂O₃ to produce Mg₃Al₂（Si O₄）₃.When more Si O₂ is added,it mainly reacts with ZnO to form Zn₂Si O₄.The moderate of Si O₂ can improve the bulk density of ZnO linear resistance,while too much Si O₂ will seriously affect the denseness of ZnO linear resistance.When the amount of Si O₂ doping is 0.5 wt.%,the bulk density of the sample is 5.017 g/cm~3,but its electrical properties become worse,with a nonlinear coefficient of 1.11 and a resistance temperature coefficient of-4.97×10^-3/°C.（3）ZBS can promote the sintering of ZnO linear resistance,and significantly improve the density and resistive temperature coefficient of the sample.When the amount of ZBS doping is 0.5 wt.%and the sintering temperature is 1150℃,the ZnO linear resistor has the best overall performance,with a bulk density of 5.070 g/cm~3,a nonlinear coefficient of 1.06 and a resistance temperature coefficient of 1.57×10^-3/℃.