Flexible thermal-insulation blankets made of ceramic fibers can be protected against weather and handling by attaching thin metal face sheets. In applications in which the blankets are exposed to gas flows, the face sheets also afford protection against flow-induced stresses and help reduce aerodynamic drag by providing smoother flow surfaces.
Typically, a metal sheet to be attached to a ceramic blanket has a thickness of 5 mils ( ≈ 0.13 mm) or less and is made of titanium, aluminum, chromium, niobium, or alloys of these elements. The blanket can be made of fibers of silica, aluminoborosilicate, silicon carbide, and/or other ceramic materials. Optionally, in preparation for attachment of the metal sheet, the ceramic fabric on the attachment surface of the blanket can be precoated with a thin layer of nickel to improve its bonding properties.
Small dots of a metal or ceramic brazing material are placed on the attachment surface of the blanket (see figure). Preferably, the dots are between 1/8 and 1/4 in. (about 3 to 6 mm) square and positioned either randomly or in a regular pattern at intervals of about 1 in. (≈ 2.5 cm). The metal or ceramic brazing material can be any of several commercial formulations that both wet the ceramic fabric and form metallic bonds with the metal sheet when heated to the brazing temperature. Suitable ceramic brazing materials include ceramic-precursor adhesives based on silica, alumina, and/or zirconia. Suitable metal brazing materials include copper/silver, copper/gold, and copper/silver/gold alloys that contain titanium and/or vanadium as wetting agents.
The metal sheet is placed over the dots, then the resulting sandwich is heated to a temperature of about 1,800 °F (about 980 °C) in a reducing atmosphere or in a vacuum to effect brazing. Finally, the sandwich is cooled to room temperature, leaving the metal sheet strongly bonded to the blanket at the dots.
This work was done by Daniel J. Rasky, Paul M. Sawko, Paul Kolodziej, and Demetrius A. Kourtides of forAmes Research Center.
This invention has been patented by NASA (U.S. Patent No. 5,744,252). Inquiries concerning nonexclusive or exclusive license for its commercial development should be addressed to
the Patent Counsel
Ames Research Center; (650) 604-5104
Refer to ARC-11989