英文摘要: |
NTC Thermistor working between 0℃~300℃ has to sustain the temperature shock of 100℃ to 900℃ and high temperature and vacuum environment at 900℃, 10-3Pa. It is required that the R-T property change rate lower than demanded after storing for some time in such conditions. For these objectives a proper material prescription and sealing technique are required to retain the stabilization of high temperature and resolve the problem of deoxidization fail. In this paper, we develop a kind of high temperature NTC therminstor which could be used in vacuum of 10-3Pa with the basic preparation technique and electric conduction mechanism of thermistors. The growth of grain boundary after sintering, chemical component , microscopic structure and ceramic condensation are analyzed. Through the high temperature stability and resistant reappearance, the factor affecting the stability of the devices is discussed. We find out an acceptable sealing solution to keep them air hermetic. The result of testing shows that these products have an satisfying performance to fit the demands. The research also analyzes NTC thermistor materials deoxidization fail mechanism at high temperature and in vacuum. According to the methods of Reliability Physics, we collect the fail data of different material’s composition and different experiment conditions in vacuum, disscuss the reason and the mechanism. We make a prediction in some sides and prove them to be true with experiments and analysis. Finally, we summarize all the fail mode and give a solution of them. The research provides theoretical basis to resolve the problem technically for the further work. The conclusions are as follows: 1. Adding Al2O3 and MgO in traditional NTC materials could help to enhance the compactability of crystal. The structure could not be changed after sintering and still is spinel and sosoloid. These materials have a Negative Temperature Coefficient. The resistant and B value could be adjusted by changing the content of Al2O3 and MgO to fit the production demands. 2. Mixing the Co-Mn-Ni-Mg-O and Co-Mn-Ni-Al-O which has a small resistance change and converse changing trends after heat treatment, could get a good resistant replicability prescription, other characteristics are also good for use. 3. Material’s stopping property will be enhanced if the omniseal method is used. Using multi-layer sealing method, the heating-soften and coefficient of expansion problem are initiative resolved. The self controlled phosphate cement reinforced the stability at high temperature and the above sealing structure could perfectly back up the mechanical behavior of elements. 4. The fail in vacuum is mainly be caused by surface deoxidization and initial defect balance change. There is a critical temperature of deoxidization which dependes on the formula and surface appearance of materials. All of the factors,such as prescription ,sealing system heating stability and coefficient of expansion problem of connecting system will affect the fail at high temperature and in vacuum. |