Outgassing is the release of a gas trapped or frozen in some material. This is not to be confused with sublimation or boiling which are phase transitions of a substance into a gas.

Outgassing is a problem encountered in high-vacuum applications. For example, NASA maintains a list of low-outgassing materials to be used for spacecraft that have sensitive optics, as outgassing can cause deposits on mirrors, optical lenses, thermal radiators, or solar cells. Materials not normally considered absorbent can release enough light molecules to interfere with industrial or scientific processes. Even metals and glasses can release gases from cracks or impurities, but sealants, lubricants, and adhesives are the most common cause. The rate of outgassing increases at higher temperatures. For most solid materials, the method of manufacture and preparation can reduce the level of outgassing significantly. Cleaning surfaces or baking individual components or the entire assembly before use can drive off volatiles.

NASA's Stardust spaceprobe suffered reduced image quality http://stardust.jpl.nasa.gov/news/vision.html due to an unknown contaminant that had condensed on the CCD sensor of the navigation camera. A similar problem affected the Cassini-Huygens spaceprobe's Narrow Angle Camera http://saturn.jpl.nasa.gov/news/press-releases-02/20020723-pr-a.cfm , but was corrected by repeatedly heating the system to 4 degrees Celsius.

Outgassing can also refer to the source of the tenous atmospheres of some rocky planets or moons.

See Also

• Vacuum
• Outgassing Data for Selecting Spacecraft Materials Online http://outgassing.nasa.gov/
• Outgassing Data For Common Materials http://www.ee.ualberta.ca/~schmaus/vacf/outgas.html