OXIDATION BEHAVIOR OF PITCH BASED CARBON-FIBERS

Oxidation behaviour of a variety of carbon fibers made from isotropic as well as mesophase pitch has been studied. The microstructure of these carbon fibers has been studied using SEM Optical Microscope, and x-ray diffractometer. After graphitization, the carbon fibers made from isotropic pitch did not exhibit any structural pattern under SEM or the optical microscope. However, the crystallite parameters did improve significantly. Some mesophase pitch based carbon fibers are found to possess sheath and core type microstructure, the sheath being made of sheet-like graphitic layers laid parallel to the fiber's axis while others exhibit uniform structure wherein the graphitic sheets are parallel to the radius or diameter of the fibers and run along the length of the fibers. The oxidation behaviour of the fibers has been correlated with their microstructure and crystallite parameters. Carbonized fibers made from isotropic pitch exhibit the least oxidation resistance. In the case of fibers having a sheath and core microstructure, the oxidation of the core starts at a relatively lower temperature than that of the sheath. Carbon fibers having higher La value are found to have higher oxidation resistance. The reaction rates of different carbon fibers are not affected much with burn-off up to 80% at a particular temperature. The apparent activation energies vary from 112 kJ/mole to 205 kJ/mole for different carbon fibers. © 1990.