[NZP], NAZR2P3O12-TYPE MATERIALS FOR PROTECTION OF CARBON-CARBON COMPOSITES

Carbon-carbon composites, if not suitably protected, suffer from the p roblem of oxidation of the surface in normal atmospheres at temperatur es above 350 degrees C. For this reason they need to be protected from oxidizing environments by either using an impermeable coating, or usi ng a sacrificial protective coating of a suitable material, and/or dop ing of an oxidation inhibitor in the carbon. In this study we have use d a new family of materials with tailorable thermal expansion characte ristics, namely, the [NZP] family as the materials for developing a su itable coating material for C-C composites. The candidates selected fo r matching thermal expansion with that of carbon are Ca0.5Sr0.5Zr4P6O2 4, SrZr4P6O24, and Ba1.175Zr4P5.65Si0.35O24. They can be sintered in i nert atmosphere without decomposition of the phases, and can be hot-pr essed in inert atmosphere with C-C composites at 1250 degrees C withou t decomposition or chemical interaction. They are stable in the presen ce of carbon up to 1200 degrees C for at least a period of 4 h. They a lso do not show any weight loss after exposure to various temperatures up to 1200 degrees C for 4 h.