Improvement in properties and air oxidation resistance of carbon materials by boron oxide impregnation

Boron oxide (B2O3) has been impregnated into a high-density isotropic graphite block and a felt carbon fiber reinforced carbon composite (C-C composite). Impregnation was carried out at 1200 degrees C under a pressure of 15 MPa for 1 hour. The bulk density of the original graphite and C-C composite increased by 12% and 20% respectively as a result of impregnation. the mechanical properties of these materials were improved significantly, and the thermal conductivity slightly increased. Gas permeability was reduced by B2O3 impregnation to the order of 10(-5) cm(2)/s from 10(-1) cm(2)/s of the original graphite, and to 10(-2) cm(2)/s from 10 cm(2)/s of the original C-C composite. Oxidation loss by air of both B2O3-impregnated materials appeared to be almost suppressed at temperatures below 800 degrees C. Serious oxidation loss was observed in both the impregnated materials by exposing to air for several hours at 850 degrees C because of loss of B2O3 from the specimen. Copyright (C) 1997 Elsevier Science Ltd.