STRUCTURAL DEVELOPMENT IN MESOPHASE PITCH-BASED CARBON-FIBERS PRODUCED FROM NAPHTHALENE

Chemical impurities (principally sulfur) derived from petroleum-based precursor materials can impact the graphitization process by volatiliz ing during high temperature thermal treatment. In an attempt to elimin ate the crystal damage caused by the evolution of sulfur-bearing gases from petroleum-based fibers, the present research utilizes a chemical ly pure precursor synthetically derived from naphthalene. Structural a nd chemical changes were then monitored as a function of heat treatmen t temperature with X-ray diffraction and spectroscopic techniques in a n attempt to better understand how the graphitic crystal structure dev elops in these materials. As is the case with fibers produced from alt ernative precursors, gas evolution during the thermolysis region (i.e. < 1000 degrees C) damaged the crystal structure of the synthetically- derived fibers. Although this damage cannot be eliminated, optimizatio n of all phases of fiber production can minimize the extent of crystal damage incurred during thermal processing. An ideal thermal treatment is also proposed which maximizes various physical properties by manip ulating crystal structure. ''Optimization'' consisted of determining t he relationships between structural properties and various physical pr operties (namely electrical resistivity and tensile modulus) of AR-der ived carbon fibers. Using these relationships, the crystal structure i n these fibers was manipulated (i.e. optimized) by controlling the the rmal treatment process. Variables such as heating rate, dwell time and firing atmosphere were investigated. (C) 1997 Elsevier Science Ltd.