Carborane-catalyzed graphitization in polyarylacetylene-derived carbon-carbon composites

Boron in the form of a carborane compound, C 2B 10H 12, was used to catalytically graphitize a polyarylacetylene (PAA) resin, typically a nongraphitizing carbon, in bulk form and in a carbon-carbon (C-C) composite. In bulk form, significant graphitization was observed after heat treatment to 1800°C; complete graphitization was realized at 2400°C. Similar results were found for a PAA-derived carbon matrix in a unidirectional C-C composite. The effect of carborane addition on the mechanical properties of C-C unidirectional composites of PAA and T-50 carbon fibers was also examined. After heat treatment to 1100°C, the tensile strength of impregnated unidirectional fiber tows increased significantly with increasing concentration of carborane. The increase in tensile strength was accompanied by increased fiber pullout, suggesting that interface weakening decreases the tendency for matrix-dominated brittle fracture. After heat treatment to 1800°C and above, the carborane decreased the strength of the composites, but substantially increased the modulus. Catalytic graphitization of PAA offers a major potential advantage of obtaining graphitic matrices in C-C without the disadvantages of conventional pitch processing. In addition, the much lower temperatures required for catalytic graphitization would enable processing temperatures for C-C to be reduced significantly.