Sublimation and deposition of carbon during internal resistance heating ofcarbon fibers

A carbon fiber tow subjected to internal resistance heating often breaks wh en its surface temperature is raised higher than about 2200 degrees C. In t his study, the cause of the tow breakage was investigated. Internal resista nce heating gives rise to a large temperature distribution in the tow cross section, the temperature being at a maximum in the central region of the t ow cross section. Because of this temperature distribution, carbon filament s in the tow are sublimated from the central region of the tow cross sectio n, leaving a growing cavity; as a result the tow breaks. Some of the sublim ated carbon deposits on the filaments in the low temperature region surroun ding the sublimating region, forming a laminar texture around the filament surface. The structure of the deposited carbon was investigated by reflecte d light microscopy, by scanning electron and transmission electron microsco py, and by electron and wide-angle X-ray diffraction. The deposited carbon was found to be composed of carbon layer stacks with low in-plane stacking regularity. (C) 1999 Kluwer Academic Publishers.