Oxidation inhibition of carbon fibre preforms and C/C composites by H3PO4

Carbon preforms and CIC composites were treated with a H3PO4 aqueous solution in order to lower their oxidation rate. H3PO4 groups are adsorbed on carbon at room temperature. Rising the temperature results in the decomposition of the adsorbates and the formation at 600 degrees C of C-O-P bonds. Hence, carbon active sites are blocked and oxidation of carbon is limited. Further, phosphate groups neutralize catalytic impurities present at the surface of the carbonaceous material. Nevertheless, the desorption and the elimination of phosphate groups which occur at 950 degrees C, limit the efficiency of this treatment to lower temperatures. (C) 1998 Elsevier Science Limited. All rights reserved.