Carbon fiber based composites exhibit very good thermal and mechanical properties under inert atmospheres but require a protection in oxidising environments. To date, the best candidates for this protection are borides and carbides, despite being difficult to sinter. A new process has been developed for the elaboration of coatings and monoliths in the HfB2-SiC system. The microstructure was characterized using various techniques such as porosimetry, XRD, SEM, TEM, microanalysis and AES. The behaviour of such materials has been studied in the 800-1700degreesC temperature range in flowing O-2/He mixtures (PO2 = 10(2) to 2.10(4) Pa). The good oxidation resistance up to 1700degreesC is explained by the diffusion of oxygen through a protective borosilicate layer when the composition changes with a release of boron species and a progressive dissolution of HfO2.
