Structural development in mesophase pitch based carbon fibers produced from naphthalene

Abstract

Chemical impurities (principally sulfur) derived from petroleum-based precursor materials can impact the graphitization process by volatilizing during high temperature thermal treatment. In an attempt to eliminate the crystal damage caused by the evolution of sulfur-bearing gases from petroleum-based fibers, the present research utilizes a chemically pure precursor synthetically derived from naphthalene. Structural and chemical changes were then monitored as a function of heat treatment temperature with X-ray diffraction and spectroscopic techniques in an attempt to better understand how the graphitic crystal structure develops in these materials. As is the case with fibers produced from alternative precursors, gas evolution during the thermolysis region (i.e. < 1000 °C) damaged the crystal structure of the synthetically-derived fibers. Although this damage cannot be eliminated, optimization 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 manipulating crystal structure. “Optimization” consisted of determining the relationships between structural properties and various physical properties (namely electrical resistivity and tensile modulus) of AR-derived carbon fibers. Using these relationships, the crystal structure in these fibers was manipulated (i.e. optimized) by controlling the thermal treatment process. Variables such as heating rate, dwell time and firing atmosphere were investigated.