Mesophase pitches as matrix precursor of carbon fiber reinforced carbon .3. Mechanical properties of composites after carbonization and graphitization treatment

Unidirectional (UD) composites, fabricated with surface-oxidized HT carbon fibers (Magnamite AS4, Hercules) and with two mesogenic pitches and two mesophase pitches, were stabilized at 1 MPa oxygen pressure and 200 degrees C to various amounts of oxygen uptake, carbonized and graphitization-treated at 2100 degrees C. Dimensional changes and bulk densities of the composites, carbon yields of the matrix, and mechanical properties of the composites were determined. Bulk density, Young's modulus, and flexural strength increase with increasing oxygen uptake or increasing degree of matrix stabilization. With each pitch, maximum values were found in the range of optimum stabilization as defined in Part II of the paper. An over-stabilization should be avoided because graphitizability of the matrix is reduced without an improvement of the mechanical properties. In view of mechanical properties, the best results were found with a mesophase pitch followed by a mesogenic pitch, both produced by isothermal pyrolysis. Copyright (C) 1996 Elsevier Science Ltd