REMARKS FOR THE IMPROVEMENT OF THE RESIST ANCE AGAINST OXIDATION OF CARBON-BEARING MATERIALS

The examination of the criteria for the protective coatings of high te mperature ceramic composites shows that the best solution is only obta ined by successive layers having different and complementary functions with the external coating with silica and/or alumina bearning oxides. Thermodynamic modelisation of the SiO2-Al2O3-MgO system shows the int erest of a ''viscous oxides'' external coating. The results indicate t hat the SiO2-ZrO2 system could be interesting to study, because the co ating could be obtained by a controlled oxidation of a biphasic deposi t. The feasibility has been checked by thermodynamic. Such a deposit c ould be conceived as like a gradient layer and is compatible with the actual protecting coating of carbon-carbon composites. Other solutions based on dispersed phases or multi layered architecture are evocated.