材料物理与化学研究室知识库

工作温度在0℃～300℃的NTC（Negative Temperature Coefficient，负温度系数）热敏电阻器，为满足特殊的使用要求，需经受100℃至900℃的温度冲击和900℃、10-3Pa 下的高温真空环境。要求在此条件下保存一定时间后，其阻温特性变化小于规定值。为此，需要研究合理的原料配方和封装工艺保持其在高温下的稳定性，以解决真空条件下的脱氧失效问题。本论文结合热敏电阻的基本制备工艺及其导电机理，研制一种耐高温900℃，在真空10-3Pa下应用的NTC耐高温热敏电阻器，研究了烧结后陶瓷的晶界生长及化学组成、显微结构及陶瓷致密性；从高温稳定性和阻值复现性等方面研究了影响耐高温热敏电阻稳定性的因素；研究了耐高温热敏电阻的封装结构，找出了一种合理的封装工艺，经测试，元件成品的各项指标能够满足要求。对于热敏电阻器的真空脱氧失效问题，本论文进行了NTC 热敏电阻材料高温真空脱氧失效机理的初步研究。此研究按照可靠性物理的分析方法，实验并收集失效现象的各种数据，对失效的原因和机理进行了分析，在失效条件方面作出了预测，并通过实验初步验证了预测的准确性，最后总结出元件的几种失效模式并提出了解决方案，为从技术上解决这一问题提供理论基础和依据。研究得到了如下的结论：1. 在传统的过渡金属氧化物热敏材料中，加入Al2O3 和MgO 有利于晶体致密性的提高，烧结后的陶瓷晶体结构并不改变，形成尖晶石结构的固溶体，具有NTC 的热敏特性，可以通过调节Al2O3 及MgO 的量进行阻值和B 值的调节，适于耐高温热敏电阻器的生产。2. 将热处理后阻值变化小， 且阻值变化规律相反的Co-Mn-Ni-Mg-O 和Co-Mn-Ni-Al-O系材料混合，获得的新材料具有较好的热处理复现性。阻值和B值等电学性能也符合生产要求。3. 采用全密闭方式进行高温热敏电阻的封装，提高了材料的密闭性，应用多层封装方案，解决了封装材料的高温软化和膨胀系数不匹配的问题。自制的磷酸盐高温水泥，提高了耐高温热敏电阻器的高温稳定性。采用双层密闭封装结构，提高了热敏电阻器的机械性能。4. 热敏电阻的高温真空失效主要由材料表面氧离子解吸附和内部缺陷平衡的改变引起，高温真空失效具有临界温度，该温度与材料的种类和表面形貌有关。元件的配方、封装系统的耐高温性以及引线与各部分膨胀系数均会对高温真空失效产生影响。

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.