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

Abstract

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 micro- structures and an important relationship is existed between thermoelectric property and orientation of pyrocarbon. See- beck 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.