Outgassing - China Wall Stone Texture - Wall Stone Texture

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Outgassing in a vacuum
Outgassing is a challenge to creating and maintaining clean high-vacuum environments. NASA maintains a list of low-outgassing materials to be used for spacecraft, as outgassing products can condense onto optical elements, thermal radiators, or solar cells and obscure them. Materials not normally considered absorbent can release enough light-weight molecules to interfere with industrial or scientific vacuum processes. Even metals and glasses can release gases from cracks or impurities, but moisture, sealants, lubricants, and adhesives are the most common sources. The rate of outgassing increases at higher temperatures because the vapour pressure and rate of chemical reaction increases. 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 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, but was corrected by repeatedly heating the system to 4 degrees Celsius.
Outgassing from rock
Outgassing is the source of many tenuous atmospheres of terrestrial planets or moons. Many materials are volatile relative to the extreme vacuum of space, such as around the Earth's Moon, and may evaporate or even boil at ambient temperature. Materials on the lunar surface have completely outgassed and been ripped away by solar winds long ago, but volatile materials may remain at depth. Once released, gases almost always are less dense than the surrounding rocks and sand and seep toward the surface. The lunar atmosphere probably originates from outgassing of warm material below the surface. At the Earth's tectonic divergent boundaries where new crust is being created, helium and carbon dioxide are some of the volatiles being outgassed from mantle magma.
Outgassing in a closed environment
Outgassing can be significant if it collects in a closed environment where air is stagnant or recirculated. This is, for example, the origin of new car smell. Even a nearly odourless material such as wood may build up a strong smell if kept in a closed box for months. There is some concern that softeners and solvents that are released from many industrial products, especially plastics, may be harmful to human health. Some types of RTV sealants outgas the poison cyanide for weeks after application[citation needed]. These outgassing poisons are of great concern in the design of submarines and space stations.
See also
Volatile organic compound
Note: VOCs don't outgas; they create a significant vapor pressure not because they have absorbed gas, but because they break down (depolymerize) due to time, light, and heat.
External links
Outgassing Data for Selecting Spacecraft Materials Online (NASA database)
Outgassing Data For Common Materials
Outgassing data for some nonmetallic materials (table 3)
ESA Outgassing Data for Spacecraft Materials according to ECSS-Q-70-02
Notes
^ Strong, John (1938). Procedures in Experimental Physics. Bradley, IL: Lindsay Publications. , Chapter 3
External link - Outgassing data for some nonmetalic materials (table 3) pdf doesn't work.
Categories: Vacuum | Gas technologiesHidden categories: Articles needing additional references from September 2007 | All articles needing additional references | All articles with unsourced statements | Articles with unsourced statements from April 2009
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This article was published on 2011/04/07