Outgassing
Outgassing(sometimes calledoffgassing,particularly when in reference toindoor air quality) is the release of agasthat was dissolved, trapped,frozen,orabsorbedin some material.[1]Outgassing can includesublimationandevaporation(which arephase transitionsof a substance into a gas), as well asdesorption,seepagefrom cracks or internal volumes, and gaseous products of slowchemical reactions.Boilingis generally thought of as a separate phenomenon from outgassing because it consists of a phase transition of a liquid into avaporof the same substance.
In a vacuum
[edit]Outgassing is a challenge to creating and maintaining clean high-vacuumenvironments.NASAandESAmaintain lists of materials with low-outgassing properties suitable for use inspacecraft,as outgassing products can condense onto optical elements,thermal radiators,orsolar cellsand obscure them. Materials not normally considered absorbent can release enough lightweightmoleculesto interfere with industrial or scientific vacuum processes.Moisture,sealants,lubricants,andadhesivesare the most common sources, but evenmetalsandglassescan release gases from cracks or impurities. The rate of outgassing increases at highertemperaturesbecause thevapor pressureand rate of chemical reaction increases. For most solid materials, the method of manufacture and preparation can reduce the level of outgassing significantly. Cleaning of surfaces, or heating of individual components or the entire assembly (a process called "bake-out") can drive offvolatiles.
NASA'sStardustspace probesuffered reduced image quality due to an unknown contaminant that had condensed on theCCDsensor of the navigation camera.[2]A similar problem affected theCassinispace probe's Narrow Angle Camera, but was corrected by repeatedly heating the system to 4 °C.[3]A comprehensive characterisation of outgassing effects usingmass spectrometerscould be obtained for ESA'sRosettaspacecraft.[4]
Natural outgassing is commonplace incomets.[5]
From rock
[edit]Outgassing is a possible source of many tenuousatmospheresofterrestrial planetsor moons.[6]Many materials are volatile relative to the extreme vacuum ofouter space,and may evaporate or even boil at ambient temperature. Materials on thelunar surfacehave completely outgassed and been blown away bysolar windslong ago, but volatile materials may remain at depth. Thelunar atmosphereprobably originates from outgassing of warm material below the surface.
Once released, gases almost always are lessdensethan the surroundingrocksandsandand seep toward the surface.Explosive eruptionsof volcanoes result from water or other volatiles outgassed frommagmabeing trapped, for example by alava dome.At the Earth'stectonic divergent boundarieswhere newcrustis being created,heliumandcarbon dioxideare some of the volatiles being outgassed frommantlemagma.Alpha decayofprimordial radionuclides(and their decay products) produces the vast majority of the helium that continues to gas out of rocks on terrestrial planets.
In a closed environment
[edit]Outgassing can be significant if it collects in a closed environment where air is stagnant or recirculated. For example,new car smellconsists of outgassed chemicals released by heat in a closed automobile. Even a nearly odorless material such as wood may build up a strong smell if kept in a closed box for months. There is some concern thatplasticizersandsolventsreleased from many industrial products, especially plastics, may be harmful to human health.[7]Long-term exposure to solvent vapors can causechronic solvent-induced encephalopathy(CSE). Outgassing toxic gases are of great concern in the design ofsubmarinesandspace stations,which must have self-contained recirculated atmospheres.
In construction
[edit]The outgassing of small pockets of air near the surface of settingconcretecan lead to permanent holes in the structure (calledbugholes) that may compromise its structural integrity.[8][9]
See also
[edit]References
[edit]- ^Strong, John (1938).Procedures in Experimental Physics.Bradley, IL: Lindsay Publications.,Chapter 3
- ^"STARDUST Vision Nearly Restored".stardust.jpl.nasa.gov.January 11, 2001. Archived fromthe originalon April 3, 2009.
- ^"Cassini Camera Haze is Removed"(Press release).NASA&JPL.23 July 2002.Archivedfrom the original on 15 July 2024.Retrieved14 October2006.
- ^B. Schläppi, et al. (2010), Influence of spacecraft outgassing on the exploration of tenuous atmospheres with in situ mass spectrometry, J. Geophys. Res., 115, A12313,doi:10.1029/2010JA015734.
- ^De Val-Borro, M.; Rezac, L.; Hartogh, P.; Biver, N.;Bockelée-Morvan, D.;Crovisier, J.; Küppers, M.; Lis, D. C.; Szutowicz, S.; Blake, G. A.; Emprechtinger, M.; Jarchow, C.; Jehin, E.; Kidger, M.; Lara, L.-M.; Lellouch, E.; Moreno, R.; Rengel, M. (2012). "An upper limit for the water outgassing rate of the main-belt comet 176P/LINEAR observed withHerschel/HIFI ".Astronomy & Astrophysics.546:L4.arXiv:1208.5480.Bibcode:2012A&A...546L...4D.doi:10.1051/0004-6361/201220169.S2CID118376416.
- ^Shirley, J. H.; Fairbridge, Rhodes W. (2001-01-31).Encyclopedia of Planetary Sciences.Springer Netherlands.ISBN9780792367949.
- ^"Health Concerns [archived on archive.today]".United States Environmental Protection Agency.Archived fromthe originalon 2014-12-03.Retrieved2020-04-17.
- ^Thin-Patch Repair of Concrete in Wastewater Environments Using Commercially Available Cementitious Resurfacers(PDF),Concrete Repair Bulletin, January 2008, archived fromthe original(PDF)on 2020-04-17,retrieved2014-10-21
- ^Preventing Air-Induced Coating Failures on Concrete(PDF),JPCL, January 2007, archived fromthe original(PDF)on 2014-10-22,retrieved2014-10-21