SHIELDED CERAMIC COMPOSITE STRUCTURE

Alumina, zirconia, and thoria were selected for use in composite ceramic heat shields for the leading surfaces of lifting orbital re-entry vehicles. Coated columbium and molybdenum were selected for substructure materials. Commercially available low and high density alumina, zirconia, and thoria ceramics were evaluated for thermal shock resistance; and many high density, but no low density ceramics were found to be satisfactory. A sintered low density thermal shock resistace zirconia was developed, but it was difficult to reproducibly manufacture. A sintered low density thoria was developed that had low thermal shock resistance but could be reproducibly manufactured. Chemically bonded low and high density thermal shock resistant varieties of alumina, zirconia, and thoria were developed. Thermophysical properties were determined to temperatures as high as 4500 F for the ceramics utilized in this project. Analytical techniques were derived for predicting the thermal stress behavior of ceramics. Twenty-two subscale heat shield modules and three full size components were designed, fabricated and environmentally tested. (Author)