Analysis of Oxidative Stabilization of Mesophase Pitch Matrix in Carbon−Carbon Composites, with Respect to Oxygen Permeability and Crosslinking

Abstract

In the resin transfer molding (RTM) densification process, a liquid synthetic pitch is injected at high pressure into the void spaces of the carbonized porous carbon fiber−carbon matrix (C−C) composite and allowed to solidify. To prevent the expulsion of this pitch during the subsequent high-temperature carbonization, this thermoplastic pitch must be stabilized (thermoset) by crosslinking with oxygen and exposing the composite to air at a fixed temperature of 160−220 °C. The distributed layer of reacted oxygen is strongly dependent on the permeability of the gaseous oxygen across the solid mesophase pitch. The shape and penetration of the reacted oxygen profile, obtained from Auger spectroscopy by ion etching, is used to estimate the permeability of oxygen as 1.86 × 10-12 cm2/s. Furthermore, Photoacoustic sampling−Fourier transform infrared spectroscopy (PAS−FTIR) was used to characterize the matrix of the C−C samples to determine the functional group changes during oxidation, qualitatively.