Space Shuttle - Degussa Silanes in Space

Monday, October 23, 2006

When the Space Shuttle Discovery set out again in July 2006 for the ISS International Space Station, Dynasylan^® 5635 was on board for another trip into space. Produced by Degussa Aerosil & Silanes Business Unit, Dynasylan^® 5635 waterproofs the high-temperature silicon ceramics that cover the space shuttles of the US space agency NASA, protecting them against the extreme temperatures in space and during reentry into the earth's atmosphere.

The water-repellant properties of Dynasylan^® 5635, an alkylalkoxysilane, have been successfully proven in nearly 100 space shuttle launches. The water repellant is indispensable for the ceramic heat shield of the space shuttles, which are built in Cape Canaveral in the subtropical climate of Florida. There, the year-round humidity can reach as high as 95 percent. Without the water-repellant finish, the ceramic shell would quickly soak up water, and the space shuttle would take on an incalculable amount of weight. Then, as the altitude increased and the temperature dropped, this water would freeze extremely fast, only to evaporate just as fast when the space shuttle left the earth's atmosphere a few minutes after launch. This would cause cracks and breaks in the tiles.

More than 27,000 ceramic tiles go into the space shuttle's heat shield, and the water repellency is imparted partly by hand. Because the waterproofing agent normally burns out of the ceramic tiles during reentry into the earth's atmosphere, when temperatures can reach 1,400 °C (2,552 °F), the tiles have to be checked with the utmost care after each landing and then reimpregnated with the silane. About 100 kilograms of Dynasylan^® 5635 are required per shuttle flight. Degussa silanes are also used to repair the minor damage that can occur, for example, as a result of collision with dust particles. In this case, a silane-silicon carbide mixture is applied with a brush to the damaged spot.

The outer space career of Degussa silanes began as early as the mid-1980s. Prior to that, in 1984, a space shuttle had lost its outer covering during a flight into space. A subsequent investigation revealed an adhesive being tha cause of the failure. The paste that bonded the ceramic tiles with the aluminum frame of the shuttle had been destroyed by a chemical reaction, which was caused by a waterproofing agent that was unsuitable for use in outer space. Over the next two years, more than 100 different organosilanes from several suppliers were tested. Dynasylan^® 5635 prevailed over the others, because it met the strict criteria and did not impair the adhesive system. Under an exclusive license agreement, Degussa has guaranteed that it will supply NASA with Dynasylan^® 5635 until the space shuttle project reaches its expected conclusion in 2010. By then it will be replaced by the Crew Exploration Vehicle.

At ground level, the waterproofing properties of organofunctional alkylalkoxysilanes are frequently exploited in the construction industry to protect surfaces against corrosion, weather factors and graffiti (see www.protectosil.com). The history of Degussa silanes began more than 60 years ago in the former electrochemical factory in Rheinfelden. Today, the company operates four production facilities in Bitterfeld (Germany); Rheinfelden (Germany); Antwerp (Belgium) and Mobile, Alabama, in the United States.

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