The internal micro-structure is an important factor affecting the thermal conductivity of materials. In this work, the relationship between micro-structure, thermal conductivity, and temperature variation for carbon fibers (CF) are systematically studied by using the transient electrothermal technique. When the temperature is below the critical temperature (about 110 K), the internal structure of carbon fiber deteriorates, resulting in a very different behavior of thermal conductivity variation with temperature. By introducing the thermal reffusivity theory, the structure domain size of CF can be represented by the phonon mean free path at 0 K. The thermal reffusivity change of two temperature ranges is studied, and the mean free path of phonons in CF before and after deterioration can be calculated as 317 nm and 234 nm, respectively. The results are in good agreement with the crystallite grain size of 288 nm determined by Raman study. The thermal reffusivity provides another feasible method to study the relationship between structure domain size and thermophysical properties of materials.

内部微结构是影响材料导热性的重要因素。在这项工作中，使用瞬态电热技术系统地研究了碳纤维（CF）的微观结构，导热率和温度变化之间的关系。当温度低于临界温度（约110 K）时，碳纤维的内部结构会劣化，从而导致导热系数随温度变化的行为截然不同。通过引入热导率理论，CF的结构域大小可以用0 K时的声子平均自由程表示。研究了两个温度范围内的热导率变化，并分析了CF变质前后声子的平均自由程。可以分别计算为317 nm和234 nm。结果与拉曼研究确定的288 nm的晶粒尺寸非常吻合。热反射率提供了另一种可行的方法来研究结构域尺​​寸与材料的热物理性质之间的关系。