Investigation Of Y₂O₃ Doped Ca-Ce-Nb-W-O Thermistor Materials And Development Of Components

With the rapid development of science and technology, the sensors having different characteristics are widely used. Negative temperature coefficient thermistor has been widely used in industrial equipments due to its performances including fast response, high precision,low cost, and so on. Especially, the high temperature thermistor shows the promising applications in the temperature measurement and control of automobile engine. This thesis mainly studies on the doping of Ca-Ce-Nb-W-O based high temperature thermistor materials and the high temperature encapsultion process.CaCeNbWO8 thermistor material has excellent high-temperature resistance performance and high-temperature stability. High temperature thermistor ceramics based on the Y2O3-doped Ca-Ce-Nb-W-O system produced through a solid state reaction route were prepared by conventional sintering or vacuum sintering in this paper. The optimum sintering temperature was determined of by thermogravimetry-differential scanning calorimetry(TG/DSC) and dilatometry(DIL). The effects of Y2O3 content on the structure and electrical properties of the Ca-Ce-Nb-W-O materials had been studied through using X-ray diffraction(XRD), scanning electron microscope(SEM) and resistance-temperature test. The effects of the conventional sintering and vacuum sintering on the structure and electrical properties of the ceramics had been comparatively investigated. The ceramic and glass composite materials mixed with adhesive(phosphate curing agent) was used to perform encapsulation testing, and the relationship between the thermal expansion property of thermistor ceramics and the encapsulation technique was put forward. The main results are summarized as follow:(1)The main phase in the conventional sintered YxCa1-x CeNbWO8(0≤x≤0.2)ceramics was a single scheelite structure. And their resistivity decreases as the Y2O3 content increases.The conductivity of the thermistor ceramic was mainly conducted by electron hole hoppingbetween Ce3 + and Ce4 +. The resistivity was mainly decided by the Ce3 + concentration. In order to maintain electrically neutral, Ce3 + ions increased with increasing the content of Y2O3,which leads to an increase in the carrier concentration thereby decreasing the resistivity.(2)Vacuum sintering of thermistor ceramic mainly includes fergusonite and scheelite structures, and the surface had many pores. The lnρ and1000/T curve of thermistor ceramic by conventional sintering and vacuum sintering showed obvious negative temperature coefficient characteristics. The YxCa1-xCeNbWO8 thermistor ceramics by vacuum sintering showed a better linear relationship between the lnρ and 1000/T than conventional sintering.(3)The greater the content of glass, the lower sintering temperature when ceramic added different proportion glass phase was sintered under different temperatures. Dielectric loss and dielectric constant of encapsulation material increased in the temperature of 0~800℃. Both of thermistor ceramics and encapsulation material had a low thermal expansion coefficient, and show a good matching performance below 400 ℃. The thermal expansion coefficient of encapsulation material is bigger than thermistor ceramics above 400℃, resulting in thermistor layering and cracking phenomenon. Research results showed that the research and development of encapsulation material could be used in the temperature of 0 ℃ ~ 400 ℃...