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Microstructure/electrical property correlations in ceramic matrix composites.

机译：陶瓷基复合材料中的微观结构/电性能相关性。

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摘要

Three insulator-conductor composites have been studied—pressed BN-Graphite, and hot pressed BN-B4C and BN-SiC. Correlations between the microstructure of these materials and their electrical properties have been made. The microstructure of these materials was studied using x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The microstructure is anisotropic in that the BN exists in platelets that are lined up perpendicular to the hot pressing direction of the material. It was found that the amount of preferred orientation of the BN platelets in the material could be related to the resistivity and dielectric properties of the material. The orientation of the electric field with respect to the BN platelets also affected the electrical properties of the materials. Varying the ratio of insulator to conductor volume fractions can also demonstrate percolation behavior in these materials. Electrical properties of composites are highly affected by their microstructure. Therefore, electrical properties may be used to predict the microstructure of these materials. Both dc and ac electrical properties for BN-B4C and BN-SiC composites over a composition range from 100% BN to 100% B4C or SiC were obtained. These properties were then modeled using the McLachlan equation and a modified version of the Maxwell Wagner equation.; Calculated impedance spectra for Graphite-BN samples were used to study the basic shape of the impedance spectra near the percolation threshold (Φ c ≈ 0.16). It was found that large changes in properties (over 10 orders of magnitude) occurred over a short composition range. These changes affect the frequency response of not only the impedance, but also the permittivity, electric modulus and tanδ.; Electrical measurements can give information about the microstructure of a composite material. They can indicate the composition of the material and any anisotropy in the material. In a well behaved system, the orientation of the electric field with respect to a certain feature can be determined using ac measurements. However, if a system is not well behaved, the amount of information discernible diminishes. In almost any insulator- conductor system electrical measurements can indicate if a system is percolated.
机译：研究了三种绝缘体-导体复合材料：压制的BN-石墨，热压的BN-B 4 C和BN-SiC。这些材料的微观结构与其电性能之间已经建立了相关性。使用X射线衍射，扫描电子显微镜和透射电子显微镜研究了这些材料的微观结构。微观结构是各向异性的，因为BN存在于垂直于材料热压方向排列的血小板中。已经发现，BN血小板在材料中的优选取向的量可以与材料的电阻率和介电特性有关。相对于BN血小板的电场方向也影响了材料的电学性质。改变绝缘体与导体体积分数的比率也可以证明这些材料的渗透行为。复合材料的电性能受其微观结构的影响很大。因此，电性能可用于预测这些材料的微观结构。获得了组成范围从100％BN到100％B 4 C或SiC的BN-B4C和BN-SiC复合材料的直流和交流电性能。然后，使用McLachlan方程和Maxwell Wagner方程的修改版本对这些属性进行建模。使用计算得出的石墨-BN样品的阻抗谱来研究在渗滤阈值（Φ c ＆ap; 0.16）附近的阻抗谱的基本形状。发现在短的组成范围内发生了性质的大变化（超过10个数量级）。这些变化不仅影响阻抗的频率响应，而且影响介电常数，电模量和tanδ。电气测量可以提供有关复合材料微观结构的信息。它们可以指示材料的组成以及材料中的任何各向异性。在性能良好的系统中，可以使用ac测量来确定电场相对于某个特征的方向。但是，如果系统运行不正常，可识别的信息量就会减少。在几乎任何绝缘体-导体系统中，电气测量都可以指示系统是否被渗滤。

著录项

  • 作者

    Kokan, Julie Runyan.;

  • 作者单位

    Georgia Institute of Technology.;

  • 授予单位 Georgia Institute of Technology.;
  • 学科 Engineering Materials Science.
  • 学位 Ph.D.
  • 年度 1998
  • 页码 221 p.
  • 总页数 221
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 工程材料学;
  • 关键词

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