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

doi:10.15541/jim20140335

Abstract

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 N₂as 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.

Key words: C/C composites, thermoelectric properties, texture, preferred orientation

CLC Number:

TB33

HU Gang, ZENG Xie-Rong, MA Jun, ZOU Ji-Zhao, PENG Biao-Lin. Dependence of the Texture on the Thermoelectric Properties of C/C Composites[J]. Journal of Inorganic Materials, 2015, 30(4): 357-362.

Figures/Tables 8

Table 1 MCVI process parameters of C/C composites

Sample	N₂:CH₄	Pressure/kPa	Temperature/℃	Residence time/s
ISO	4:1	20	1200	0.02
LT	4:1	20	1200	0.04
MT	4:1	20	1200	0.06
HT	4:1	20	1200	0.08

Fig. 1 PLM and SEM images of C/C composites with various microstructures (a) ISO; (b) LT; (c) MT; (d) HT

Fig. 2 HRTEM images and selected area electron diffraction of C/C composites (a) LT; (b) HT

Fig. 3 XRD patterns of C/C composites with different microstructures

Table 2 Diffraction parameters of C/C composites

Sample	2θ/(°)	d₀₀₂/nm	L_c/nm	g
ISO	25.847	0.3444	4.59	-4.8%
LT	25.924	0.3434	4.85	6.8%
MT	25.947	0.3431	4.92	10.3%
HT	25.962	0.3429	7.56	12.6%

Fig. 4 Raman spectra of C/C composites with different microstructures

Fig. 5 Influence of microstructure of C/C composites on thermoelectric parameters (a) Seebeck coefficient; (b) Electrical conductivity; (c) Thermal conductivity; (d)ZT

Fig. 6 Evolution of active sites with the change of aromatic- carbon (+indicates peripheral sites)

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