Investigation of thermal and hydrogen effects on emissivity of refractory metals and carbides
Investigation of thermal and hydrogen effects on emissivity of refractory metals and carbides
复制标题
DOI：
10.1016/0921-5093(95)09793-7
复制
发表时间：
1995-11
期刊：
影响因子：
6.4
通讯作者：
Y. Ozaki;R. Zee
中科院分区：
文献类型：
--
作者：
Y. Ozaki;R. Zee
直接热电转换系统在高温下运行，以确保此类系统的高功率密度和适当的热传递，这对其稳定性至关重要。在这种温度范围内，辐射是一种主要的热传递手段，因此，控制辐射部件的表面特性是一个重要的问题。研究了各种高温组分的高温法向光谱发射率。研究的材料包括钨、弥散强化钨(WCVDHFC)、化学气相沉积涂层(-W)和五种碳化物(WC、TaC、NbC、ZRC和HFC)。使用单波长和双波长辐射测温仪测量光谱发射率。发现钨的发射率为0.5，即使在2723K的真空退火后仍保持恒定。这五种碳化物在真空和氢气中都暴露在高温下。结果表明，该过程是热激活的，氢气对所测试的陶瓷影响不大。碳化钨的稳定性最差，退火后转变为W2C，而NbC在类似的暴露后分解。在所研究的碳化物中，Hf碳化物和ZRC最稳定，具有最高的发射率(0.9)。从材料的热力学角度对实验观察进行了检验。研究了发射率对典型空间核动力系统热特性的影响。
Direct thermal-to-electric power-conversion systems operate at high temperatures to ensure high power density and proper heat transfer in such systems, critical to their stability. Radiation in this temperature regime is a main means of heat transfer and the control of the surface characteristics of radiative components is thus an important issue. High-temperature normal spectral emissivity of various high-temperature components was investigated. Materials examined include tungsten, a dispersion strengthened tungsten (WHfC), a chemical vapor deposition (CVD) coating (CVD-W) and five types of carbides (WC, TaC, NbC, ZrC and HfC). Spectral emissivities were measured using single- and dual-wavelength radiation thermometries. Emissivity of tungsten was found to be 0.5 and remained constant even after vacuum annealing up to 2723 K. The five carbides were exposed to high temperatures, both in vacuum and in hydrogen. Results show the process to be thermally activated and hydrogen to have little effect on the ceramics examined. Tungsten carbide was the least stable and it transformed into W2C upon annealing whereas NbC decomposed after similar exposure. Hafnium carbide and ZrC were found to be the most stable and possessed the highest emissivity (0.9) among the carbides investigated. The experimental observation was examined in terms of thermodynamics of the materials. The implications of emissivity on the thermal characteristics of a typical space nuclear power system were examined.