INVESTIGATION OF THE LOW-TEMPERATURE OXIDATION EFFECT ON THE STRUCTURE AND MECHANICAL PROPERTIES OF C/C COMPOSITE

The oxidation of carbon-carbon (C/C) composite materials with a pyrocarbon matrix at temperatures of 570-600oC to a mass loss of 90% by weight was studied. The formation of micropores with a size of up to 2 nm on the surface of carbon fibers is proved by the method of small-angle X-ray scattering. Tests for three-point transverse bending of C/C composite samples with the extent of reaction X-c = 0-0.6 were performed. A decrease in the tensile strength and elastic modulus during bending was found in the intervals from 315 to 1 MPa and from 60 to 0.2 GPa, respectively. This is the result of violations of the adhesive interaction in the filler-matrix system, increasing the degree of defect structure because of burnout pyrolysis residue of the binder, nucleation and evolution of microporosity, and also due to the decrease in cohesive strength of the fibers as a result of increase of their defects. The use of the specific surface area as a parameter for evaluating and controlling the structural stability of composite materials in open systems is proposed.