The usage of carbon fibers (CFs) for high-temperature applications has been increasing in recent years. However, the determination of thermal properties at high temperatures is a challenging task. In this study, the thermal conductivity of two different types of CF having a diameter in the range from 5–7 $\mathrm{\mu }$ m, as a function of temperature, was examined by using the optothermal Raman method. Raman spectroscopy was first used to obtain the structural organization and structural homogeneity of the fibers. Then, owing to the fact that Raman spectra are sensitive to laser excitation power and external temperature, Raman spectroscopy was used as a contactless thermometer to determine the local temperature rise of the fibers. A formula was derived by solving the heat diffusion equation for cylindrical fibers and a set of boundary conditions, similar to the experimental conditions, which allows accurate estimation of longitudinal thermal conductivity. The results are discussed in relation with the phonon scattering theory and can be attributed to the combined effect of scattering from defects. The radiative and convective heat losses were estimated, and their influence on thermal conductivity was also determined.

中文翻译：

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光热拉曼技术测定低阶碳纤维的纵向导热系数

近年来，碳纤维（CF）在高温应用中的使用不断增加。然而，确定高温下的热性能是一项具有挑战性的任务。在这项研究中，两种不同类型的 CF 的热导率在 5-7 范围内$\mathrm{\mu }$m 作为温度的函数，通过光热拉曼方法进行了检查。拉曼光谱首先用于获得纤维的结构组织和结构均匀性。然后，由于拉曼光谱对激光激发功率和外部温度敏感，拉曼光谱被用作非接触式温度计来确定光纤的局部温升。通过求解圆柱形纤维的热扩散方程和一组类似于实验条件的边界条件，导出了一个公式，可以准确估计纵向导热系数。结果与声子散射理论有关，可归因于缺陷散射的综合效应。估计了辐射热损失和对流热损失，并确定了它们对热导率的影响。