炭/炭复合材料微观结构对热电性能的影响

Dependence of the Texture on the Thermoelectric Properties of C/C Composites

采用微波化学气相渗透工艺,以炭毡为预制体,甲烷为前驱气体,氮气为载气,制备了具有不同微观组织结构的炭/炭复合材料。通过偏光显微镜、场发射扫描电子显微镜、透射电子显微镜、X射线衍射仪和拉曼光谱仪表征了复合材料的结构,通过热电性能测试仪和激光热导仪测试了其热电性能。结果表明,炭/炭复合材料具有正的热电效应,且复合材料的热电性能与热解炭的取向性有很大的关系:从各向同性、低织构、中织构到高织构,其Seebeck系数、电导率和热导率逐渐增加,同时织构化的增强对载流子的影响大于对声子的影响,进而使热电优值ZT随着织构化的增强逐渐增大。

C/C composites with different microstructures were fabricated by microwave chemical vapor infiltration（MCVI） using carbon felt as fiber preform, CH4 as precursor gas and N2 as diluent gas. The different microstructures of C/C composites were characterized by polarizing microscope（PLM）, scanning electron microscope（SEM）, transmission electron microscope（TEM）, X-ray diffraction（XRD） and Raman spectra. Thermoelectric properties were systematically investigated via thermoelectric performance testing instrument（ZEM-2） and laser thermal conductivity instrument（TC-9000H）. The results reveal that positive Seebeck coefficient is obtained from C/C composites with different microstructures and an important relationship is existed between thermoelectric property and orientation of pyrocarbon. Seebeck coefficient, electrical conductivity and thermal conductivity are increased gradually with the texture of pyrocarbon evolved from isotropy, low texture and middle texture to high texture. With the texture being reinforced, it has a more important influence on carriers than on phonons. As a result, the merit ZT is increased with the reinforce of the texture.