[NZP], NaZr2P3O12-type materials for protection of carbon-carbon composites

Carbon-carbon composites, if not suitably protected, suffer from the problem of oxidation of the surface in normal atmospheres at temperatures above 350 °C. For this reason they need to be protected from oxidizing environments by either using an impermeable coating, or using a sacrificial protective coating of a suitable material, and/or doping of an oxidation inhibitor in the carbon. In this study we have used a new family of materials with tailorable thermal expansion characteristics, namely, the [NZP] family as the materials for developing a suitable coating material for C-C composites. The candidates selected for matching thermal expansion with that of carbon are Ca0.5Sr0.5Zr4P6O24, SrZr4P6O24, and Ba1.175Zr4P5.65Si0.35O24. They can be sintered in inert atmosphere without decomposition of the phases, and can be hot-pressed in inert atmosphere with C-C composites at 1250 °C without decomposition or chemical interaction. They are stable in the presence of carbon up to 1200 °C for at least a period of 4 h. They also do not show any weight loss after exposure to various temperatures up to 1200 °C for 4 h.