• 主题
高级搜索  >
历史搜索 清空历史
首页> 外文学位 >Oxidation resistance, thermal conductivity, and spectral emittance of fully dense zirconium diboride with silicon carbide and tantalum diboride additives.
【24h】

Oxidation resistance, thermal conductivity, and spectral emittance of fully dense zirconium diboride with silicon carbide and tantalum diboride additives.

机译：具有碳化硅和二硼化钽添加剂的完全致密的二硼化锆的抗氧化性，导热性和光谱发射率。

获取原文
获取原文并翻译 | 示例
页面导航
  • 摘要
  • 著录项
  • 相似文献
  • 相关主题

摘要

Zirconium diboride (ZrB2) is a ceramic material possessing ultra-high melting temperatures. As such, this compound could be useful in the construction of thermal protection systems for aerospace applications. This work addresses a primary shortcoming of this material, namely its propensity to destructively oxidize at high temperatures, as well as secondary issues concerning its heat transport properties.;To characterize and improve oxidation properties, thermogravimetric studies were performed using a specially constructed experimental setup. ZrB 2–SiC two-phase ceramic composites were isothermally oxidized for ~90 min in flowing air in the range 1500-1900°C. Specimens with 30 mol% SiC formed distinctive reaction product layers which were highly protective; 28 mol% SiC – 6 mol% TaB2 performed similarly. At higher temperatures, specimens containing lower amounts of SiC were shown to be non-protective, whereas specimens containing greater amounts of SiC produced unstable oxide layers due to gas evolution. Oxide coating thicknesses calculated from weight loss data were consistent with those measured from SEM micrographs.;In order to characterize one aspect of the materials' heat transport properties, the thermal diffusivities of ZrB2-SiC composites were measured using the laser flash technique. These were converted to thermal conductivities using temperature dependent specific heat and density data; thermal conductivity decreased with increasing temperature over the range 25-2000°C. The composition with the highest SiC content showed the highest thermal conductivity at room temperature, but the lowest at temperatures in excess of ~400°C, because of the greater temperature sensitivity of the thermal conductivity of the SiC phase, as compared to more electrically-conductive ZrB2. Subsequent finite difference calculations were good predictors of multi-phase thermal conductvities for the compositions examined. The thermal conductivities of pure ZrB2 as a function of temperature were back-calculated from the experimental results for the multi-phase materials, and literature thermal conductivities of the other two phases. This established a relatively constant thermal conductivity of 88-104 W·K over the evaluated temperature range.;Further heat transport characterization was performed using pre-oxidized, directly resistively heated ZrB2-30 mol% SiC ribbon specimens under the observation of a spectral radiometer. The ribbons were heated and held at specific temperatures over the range 1100-1330°C in flowing Ar, and normal spectral emittance values were recorded over the 1-6 μm range with a resolution of 10 nm. The normal spectral emittance was shown to decrease with loss of the borosilicate layer over the course of the data collection time periods. This change was measured and compensated for to produce traces showing the emittance of the oxidized composition rising from ~0.7 to ~0.9 over the range of wavelengths measured (1-6 μm).
机译：二硼化锆（ZrB2）是具有超高熔化温度的陶瓷材料。这样，该化合物可用于构造用于航空航天应用的热保护系统。这项工作解决了该材料的主要缺点，即其在高温下破坏性氧化的倾向以及与它的传热性能有关的次要问题。为了表征和改善氧化性能，使用特制的实验装置进行了热重研究。 ZrB 2-SiC两相陶瓷复合材料在1500-1900°C的流动空气中被等温氧化90分钟。含有30 mol％SiC的样品形成了独特的反应产物层，具有很高的保护性。 28 mol％SiC – 6 mol％TaB2的表现相似。在较高温度下，含少量SiC的样品被证明是非保护性的，而含大量SiC的样品则由于气体逸出而产生不稳定的氧化物层。由失重数据计算得到的氧化物涂层厚度与由SEM显微照片测得的厚度一致。为了表征材料的热传递特性的一个方面，使用激光闪光技术测量ZrB2-SiC复合材料的热扩散率。使用与温度相关的比热和密度数据将这些转换为热导率；在25-2000°C范围内，热导率随温度升高而降低。 SiC含量最高的组合物在室温下显示出最高的热导率，但在超过约400°C的温度下却表现出最低的热导率，这是因为SiC相的热导率对温度的敏感度高于电导率。导电ZrB2。随后的有限差分计算可以很好地预测所检测成分的多相热导率。从多相材料的实验结果以及其他两相的文献热导率中反算出纯ZrB2的热导率随温度的变化。这在评估的温度范围内建立了88-104 W·K的相对恒定的热导率。;在光谱辐射计的观察下，使用预氧化，直接电阻加热的ZrB2-30 mol％SiC带状样品进行了进一步的热传递表征。在流动的Ar中加热色带并将其保持在1100-1330°C范围内的特定温度下，并在1-6μm范围内以10 nm的分辨率记录正常光谱发射率值。在数据收集时间段内，正常光谱发射率随硼硅酸盐层的损失而降低。测量并补偿此变化，以产生痕量，表明在测得的波长范围（1-6μm）内，氧化组合物的发射率从〜0.7升高至〜0.9。

著录项

  • 作者

    Van Laningham, Gregg Thomas.;

  • 作者单位

    Georgia Institute of Technology.;

  • 授予单位 Georgia Institute of Technology.;
  • 学科 Chemistry Inorganic.;Engineering Materials Science.
  • 学位 Ph.D.
  • 年度 2012
  • 页码 123 p.
  • 总页数 123
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

相似文献

  • 外文文献
  • 中文文献
  • 专利
获取原文

客服邮箱：kefu@zhangqiaokeyan.com

京公网安备：11010802029741号 ICP备案号：京ICP备15016152号-6 六维联合信息科技 (北京) 有限公司©版权所有

  • 客服微信

  • 服务号