Evolution of microstructure and electrical property in the conversion of high strength carbon fiber to high modulus and ultrahigh modulus carbon fiber

Evolution of microstructure and electrical property in the conversion of high strength carbon fiber (HSCF) to high modulus carbon fiber (HMCF) and ultrahigh modulus carbon fiber (UHMCF) was investigated. Longitudinal grooves on fiber surfaces became less well-defined during high temperature graphitization. The tensile modulus of carbon fibers was affected by fiber crystalline structure and it increased with decreases in the value of interlayer spacing and improvements in the value of crystallite thickness. Increases in the crystallite size almost had little effect on the tensile strength. However, a lower interlayer spacing and a higher preferred orientation could result in a higher tensile strength. The crystal structure of carbon fibers became much more ordered during high temperature graphitization. It was found that the electrical resistivity gradually decreased from 14.69 x 10(-4) Omega.cm to 9.70 x 10(-4) Omega.cm and 8.80 x 10(-4) Omega.cm, respectively, in the conversion of HSCF to HMCF and UHMCF.