Fibrous Refractory Composite Insulation Tiles

The FRCI tiles were developed by NASA's Ames Research Center, Mountain View, Calif., and were manufactured by Lockheed Missiles and Space Division, Sunnyvale, Calif.

The FRCI-12 HRSI tiles are a higher strength tile derived by adding AB312 (alumina-borosilicate fiber), called Nextel, to the pure silica tile slurry. Developed by the 3M Company of St. Paul, Minn., Nextel activates boron fusion and, figuratively, welds the micron-sized fibers of pure silica into a rigid structure during sintering in a high-temperature furnace. The resulting composite fiber refractory material composed of 20-percent Nextel and 80-percent silica fiber has entirely different physical properties from the original 99.8-percent-pure silica tiles. Nextel, with an expansion coefficient 10 times that of the 99.8-percent-pure silica, acts like a preshrunk concrete reinforcing bar in the fiber matrix.

The reaction-cured glass (black) coating of the FRCI-12 tiles is compressed as it is cured to reduce the coating's sensitivity to cracking during handling and operations. In addition to the improved coating, the FRCI-12 tiles are about 10 percent lighter than the HRSI tiles. The FRCI-12 HRSI tiles also have demonstrated a tensile strength at least three times greater than that of the HRSI tiles and a use temperature approximately 100 F higher than that of HRSI tiles.

The FRCI-12 HRSI tile manufacturing process is essentially the same as that for the 99.8-percent-pure silica HRSI tiles, the only change being in the wet-end prebinding of the slurry before it is cast. It also requires a higher sintering temperature. When the material is dried, a rigid block is produced. These blocks are cut into quarters and then machined to the precise dimensions required for each tile. The FRCI-12 tiles are the same 6- by 6-inch size as HRSI tiles and vary in thickness from 1 inch to 5 inches. They vary also in size and shape at the closeout areas and are bonded to the orbiter in essentially the same way as the HRSI tiles.

The FRCI-12 tiles are used to replace the HRSI 22-pound-per-cubic-foot tiles. The FRCI-12 tiles have a density of 12 pounds per cubic foot and provide improved strength, durability, resistance to coating cracking and weight reduction.