The microstructure of carbon/carbon composites obtained by chemical vapor infiltration of carbon-fiber felts was studied comparatively by means of Raman spectroscopy, polarized light microscopy (PLM), scanning electron microscopy (SEM), and X-ray diffraction. The matrices, which are homogeneously textured according to PLM, exhibit pronounced spatial structural gradients at the sub-μm scale if investigated by means of Raman microprobe spectrometry. The Raman and SEM observations demonstrate that the high-temperature treatment correlates with the increasing development of the graphitic ordering in low-and high-textured pyrolytic carbon matrices.
Thermal expansion of differently-textured pyrolytic carbon matrices (pyrocarbons) of carbon/carbon composites was studied with a high temperature X-ray diffraction at temperatures ranging from 25 • C to 1400 • C. The composites were synthesized by chemical vapor infiltration of a carbon fiber felt, using methane as a carbon source. From the linear dependence of the lattice displacement on temperature, coefficients of thermal expansion (CTE) of the pyrocarbons were calculated. Onedimensional thermal expansion along the (002)-direction (c-axis) of the pyrocarbons was found to be proportional to the composite synthesis temperature. A correlation between CTE and pyrocarbon texture was found: low-textured pyrocarbon with an extinction angle (Ae) of 10 • exhibits a smaller CTE of 2.02 × 10 −5 K −1 , whereas high-textured pyrocarbon with an Ae of 22 • exhibits a considerably higher CTE of 2.65 × 10 −5 K −1 . However, CTE of high-textured pyrocarbon is still smaller than that of graphite, which is 2.9 × 10 −5 K −1 .
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