中文名称： 氧化物电子陶瓷材料的微波处理研究
英文名称： Microwave processing of electronic oxide ceramics
学位类型： 博士毕业论文
作者： *** 保护隐私，隐藏
导师： *** 保护隐私，隐藏
毕业学校： *** 保护隐私，隐藏
专业： 材料物理与化学: 
毕业年份： *** 保护隐私，隐藏
分类号： TQ174
页码大小： 143页 ; 30cm
关键字： 电子陶瓷 微波烧结 热敏陶瓷 压敏陶瓷 陶瓷材料 氧化物 电子 陶瓷 材料
编号： 2180080
摘要：     本文根据微波烧结的基本原理，通过与常规烧结的对比分析，系统研究了氧化物电子陶瓷材料的微波处理，包括具有代表性的NTC热敏陶瓷，PTC热敏陶瓷，ZnO压敏陶瓷，BST热释电陶瓷等材料的微波烧结，粉体材料的微波合成，以及PZT铁电薄膜材料的微波退火研究。并从热力学和动力学观点分析了陶瓷材料的微波烧结机理。其主要内容归纳如下：
   在微波烧结工艺方面，自主设计了MgAl〓O〓-LaCrO〓型保温体，有效的解决了由于氧化物电子陶瓷样品的热性能（高热膨胀性，低热传导性）而在微波烧结的快速升降温过程中容易导致的热应力开裂问题，极大地提高了氧化物电子陶瓷微波烧结的成品率，为微波烧结技术得以在电子陶瓷行业规模化生产的应用解决了一个关键问题。采用该保温体首次成功实现了大尺寸（直径为50mm）NTC热敏陶瓷均匀无开裂成瓷的微波烧结，并获国家发明专利授权。
   首次采用NiCrAl合金管屏蔽的热电偶，避免了普通热电偶在微波场中的放电打弧(arcing)造成的测温不准，可以用于微波烧结过程的温度测量，测温精度±10℃，应用温区达到了1350℃。在微波烧结中的测温精度高于目前采用的光学高温计和红外光纤测温仪。
   通过对微波烧结缓变型Y〓掺杂(Ba〓Sr〓)TiO〓型PTC陶瓷研究，发现微波烧结可获得与常规烧结相似的PTC材料性能参数，但微波烧结使该材料的烧结温度由常规烧结的1350℃降低到微波烧结的1150℃，全程烧结时间由常规烧结的28小时降低到微波烧结的4小时，在能源节约方面具有优势。微波烧结BaTiO〓电子陶瓷时，当所加的微波功率超过一定值时，首次发现烧结样品出现轴向异常收缩现象，采用SEM、XRD等分析发现其微观结构与常规烧结有巨大的差异，这是BaTiO〓材料的晶粒在微波场中受电场力作用而发生的取向生长造成的。
   对用纳米粉体制备的ZnO压敏生坯进行了微波烧结，并与普通烧结同批次样品作性能及微结构比较。对烧结后的样品进行了微观分析和压敏特性测试，结果表明，微波烧结可使ZnO压敏材料快速成瓷，当获得样品的晶粒尺寸相同时所需微波烧结温度更低，烧结时间更短；微波烧结样品的压敏电性能参数明显优于常规烧结的样品，如采用微波烧结ZnO，1100℃/20min，获得了非线性系数α为48，漏电流I〓为0.3μA的压敏陶瓷，而同样尺寸的样品在常规烧结1100℃/120min时的非线性系数α=35，漏电流I〓=0.9μA。
   采用微波合成(Ba,Sr)TiO〓(BST)粉体可以将合成温度从常规的1100℃降至微波合成方法的900℃，合成粉体的尺寸从常规方法的320nm降至微波合成粉体的50nm。微波烧结Ba〓Sr〓TiO〓材料在1310℃/25min条件下获得了晶粒约1μm的细晶BST陶瓷。
   利用微波加热的选择性可以抑制含铅氧化物电子陶瓷中铅的挥发，从而有利于控制铅含量及材料的微结构。如对PZT铁电薄膜进行微波退火处理，不仅退火温度被显著降低，同时还阻止了氧化铅挥发造成的薄膜表面的微裂纹，从而使PZT薄膜样品上电极的完好率有大幅提高。
   通过对烧结机理的分析，推论出微波烧结过程中材料的晶界及界面处的温度比晶粒内部要高，并通过实验得到了验证。通过对NTC热敏陶瓷微波烧结和常规烧结样品的高分辨电镜(HREM)分析，观察到微波烧结样品的微观结构以点缺陷为主，而常规烧结样品的微结构中很少有点缺陷，分析认为样品在微波烧结过程的荷质传输中起主要作用的可能是点缺陷，而与常规烧结的热扩散机制不同。在钛酸钡陶瓷的微波烧结实验中，发现了当所加的微波功率超过一定值时，由于材料内部电场的作用造成样品内部轴向扩散机制的增强，从而在样品的宏观尺度上的轴向收缩率是径向收缩率的近2倍，在显微结构上观察到了晶粒的取向生长结构。并结合电磁场理论解释了发生这种现象的微观机理。

 Abstract
   According to the principle of microwave heating, the main interest of this dissertation is to systematically investigate the microwave processing of electronic ceramic materials, including microwave sintering of NTC thermistor ceramics, PTC thermistor ceramics, ZnO varistor ceramics, and BST pyroelectric ceramics, and microwave synthesis of fine ceramics powders, microwave annealing of PZT ferroelectric thin films, with comparison to the conventional heating process. The mechanism of microwave sintering in ceramic materials is analyzed according to thermodynamics. The main works of this dissertation are as follows.
   In the study of microwave sintering technology, a kind of MgAl〓O〓-LaCrO〓 insulator is designed, which solve the problem of thermal cracks easily occurred in the rapid heating and cooling of electronic oxide ceramics during the microwave sintering process, produced a homogeneous heating for the samples in the microwave sintering, and improve the production rate of electronic oxide ceramics by microwave sintering. This insulator solve a key problem which obstacle the application of microwave sintering to the production of electronic ceramics. The NTC thermistor ceramics in diameter of 50mm are successfully microwave sintered without thermal crack by the adoption of this kind insulator which has been granted with China patent.
   A kind of microwave shielded thermocouple was made for temperature measurement in microwave field. The thermocouple is sheathed with NiCrAl alloy tube to avoid the arcing in the microwave field, and has been applied for temperaure measurement up to 1350℃. This temperature measuring system has higher accuracy than the infra optic and pyrometer in the applied temperature range.
   In the research of microwave sintering of Y〓 doped (Ba〓Sr〓) TiO〓 PTC ceramics, the results showed that microwave sintering reduced the sintering temperature and total time to 1150℃ and 4 hrs to obtain the near characteristic parameters of materials, comparing to 1350℃ and 28 hrs in conventional sintering. In the study of microwave sintering of BaTiO〓 PTC ceramics, when the applied microwave power are above than a certain value, the abnormal axial shrinkage of the sintered sample will occur, by the analysis of SEM and XRD, it is found the microstructure and phase are different with conventionally sintered sample, the reason for this phenomenon is due to orientational grain growth by the action of electric field in the microwave sintering process.
   The ZnO pellets from nanopowders are microwave sintered with comparison to conventional sintering, the microstructure and electrical properties of sintered sample are analyzed. The results showed that the ZnO varistor materials can be densified by microwave sintering in lower temperature and shorter time, with same grain size as conventional sintered samples. The microwave sintered varistor samples displayed superior electrical properties than conventionally sintered sample, e. g. , the ZnO sample microwave sintering at 110 0℃/20min showed excellent I-V characteristics than the conventionally sintered samples at 1100℃/120min, with nonlinear coefficient value, α=46 and leakage current I〓=0.3 uA, comparing to conventionally sintered samples, α=35 and I〓=0.9uA.
   The (Ba, Sr) TiO〓 (BST) powder were prepared by sol-gel processing and microwave sintering technique, their properties were studied and compared with identical powder prepared by conventional technique. The results showed that the synthetic temperature of the BST powder can be reduced from 1100℃ to 900℃, The grain size of BST powder can be reduced from 320nm to 50nm. and the Ba〓Sr〓TiO〓 ceramic with fine grain size (～1μm) can be obtained at 1310℃/25 min by microwave sintering.
   The volatility of lead in Pb (Zr, Ti) O〓 (PZT) thin films can be avoided by microwave annealing, which is of benefit to the control of lead content and the microstructure of PZT films, the annealing temperature are lowered in microwave annealing and the micro-cracks are avoided comparing to conventional annealing. Microwave annealing improved the success rate of electrode pasting significantly. The results indicted that microwave annealing is advantageous to the preparation of PZT ferroelectric thin films.
   By the analysis of mechanism in microwave sintering, it is observed the temperature is higher in the grain boundary and interface of particles in the microwave sintering process, and testified by the experiment. From the analysis of HREM to NTC ceramics, it is found that the point defect are existed in microwave sintered samples, which is seldom observed in conventionally sintered samples, this is may be induced that the transfer mechanism of charge and mass in microwave sintering are different to conventional sintering. In the microwave sintering of BaTiO〓 (BT) ceramics, when the applied microwave power are above than a certain value, the diffusion are enhanced by the electrical field inside the sample, and induce the axial shrinkage rate nearly 2 times as that in radial direction, and the orientation growth of grains are observed in the microstructure of the sample. This phenomenon has been explained according to electromagnetic field theory.