ISS/SIMS Analysis of Graphite Fiber Surfaces and the Thermo-Oxidative Stability of Graphite Fiber/PMR-15 Polyimide Composites

Abstract

The long term durability of graphite fiber reinforced PMR-15 polyimide composites at 316°C and above, is dependent on two major aspects of these composite systems. These are (1) the thermal and thermo-oxidative stability of the individual components and (2) the influence of the interface region between fibers and matrix on matrix stability. In studies carried out at 316°C (600°F) on several fiber/PMR-11 and PMR-15 polyimide systems, in flowing air, it has been demonstrated that the thermo-oxidative stability of these systems is effected by fiber surface impurities, such as the alkali metal ions, sodium and potassium [1]. Gibbs et al. [2] have shown that HTS graphite fibers contain a large concentration of sodium ions on the surface, while Dryzal and Hammer [3] have demonstrated that AS graphite fibers also contain large concentrations of sodium ions relative to other graphite fibers. The overall objectives of this investigation are (1) to determine the mechanism of the thermo-oxidative process in flowing air, of several composite systems consisting of the addition polyimide PMR-15 in combination with the graphite fiber reinforcements, and (2) to determine the upper temperature limit of these composite systems.