Catalytic effect of iron oxide on carbon/carbon composites during graphitization

Coal tar pitch matrix was modified by addition of iron oxide in different proportions, i.e. 0, 1, 3 and 5% by weight. The matrix was used to develop carbon fibre reinforced composites heat treated to 1000 and 2500 degrees C, respectively. The catalytic effect of iron oxide was ascertained by measuring the physical properties viz. the inter layer spacing, thermal conductivity and flexural strength of the composites. Low concentrations of the catalyst resulted in improvement in the thermal conductivity of composites from 68 x 10(-2) W/m K for 0% to 127 x 10(-2) W/m K for 1% iron oxide concentration. The flexural strength of graphitized composites, however, showed a remarkable increase from 325 MPa for 0% to 450 MPa for 5% iron oxide concentrations. The increase in flexural strength was probably due to the development of large numbers of grain boundaries whereas the increase in the thermal conductivity was most likely due to larger crystallite size, i.e. decreases in the interlayer spacing (d(002)) of the graphitized composites. (C) 1997 Elsevier Science Ltd.