Densification and microstructure of carbon/carbon composites prepared by chemical vapor infiltration using ethanol as precursor

Abstract

Chemical vapor infiltration of carbon fiber felts with uniform initial bulk density of 0.47 g·cm−3 was investigated at the ethanol partial pressures of 5–20 kPa, as well as the temperatures of 1050, 1100, 1150 and 1200°C. Ethanol, diluted by nitrogen, was employed as the precursor of pyrolytic carbon. Polarized light microscopy (PLM), scanning electron microscopy and X-ray diffraction were adopted to study the texture of pyrolytic carbon deposited at various temperatures. A change from medium- to high-textured pyrolytic carbon was observed in the sample infiltrated at 1050°C. Whereas, homogeneous high-textured pyrolytic carbons were deposited at the temperatures of 1100, 1150 and 1200°C. Extinction angles of 19°–21° were determined for different regions in the samples densified at the temperatures ranging from 1100 to 1200°C. Scanning electron microscopy of the fracture surface after bending test indicated that the prepared carbon/carbon composite samples exhibited a pseudo-plastic fracture behavior. In addition, fracture behavior of the carbon/carbon samples was obviously effected by their infiltration temperature. The fracture mode of C/C composites was transformed from shearing failure to tensile breakage with increasing infiltration temperature. Results of this study show that ethanol is a promising carbon source to synthesize carbon/carbon composites with homogeneously high-textured pyrolytic carbon over a wide range of temperatures (from 1100 to 1200°C).