Outgassing (sometimes called offgassing, particularly when in reference to

indoor air quality Indoor air quality (IAQ) is the air quality within and around buildings and structures. IAQ is known to affect the health, comfort, and well-being of building occupants. Poor indoor air quality has been linked to sick building syndrome, reduce ...

) is the release of a

gas Gas is one of the four fundamental states of matter (the others being solid, liquid, and plasma). A pure gas may be made up of individual atoms (e.g. a noble gas like neon), elemental molecules made from one type of atom (e.g. oxygen), or ...

that was dissolved, trapped, frozen, or absorbed in some material. Outgassing can include sublimation and evaporation (which are

phase transition In chemistry, thermodynamics, and other related fields, a phase transition (or phase change) is the physical process of transition between one state of a medium and another. Commonly the term is used to refer to changes among the basic states o ...

s of a substance into a gas), as well as

desorption Desorption is the physical process where a previously adsorbed substance is released from a surface. This happens when a molecule gains enough energy to overcome the activation barrier of the bounding energy that keeps it in the surface. There ...

seepage Soil mechanics is a branch of soil physics and applied mechanics that describes the behavior of soils. It differs from fluid mechanics and solid mechanics in the sense that soils consist of a heterogeneous mixture of fluids (usually air and wat ...

from cracks or internal volumes, and gaseous products of slow

chemical reaction A chemical reaction is a process that leads to the IUPAC nomenclature for organic transformations, chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the pos ...

s. Boiling is generally thought of as a separate phenomenon from outgassing because it consists of a phase transition of a liquid into a

vapor In physics, a vapor (American English) or vapour (British English and Canadian English; see spelling differences) is a substance in the gas phase at a temperature lower than its critical temperature,R. H. Petrucci, W. S. Harwood, and F. G. Her ...

of the same substance.

In a vacuum

Outgassing is a challenge to creating and maintaining clean high-

vacuum A vacuum is a space devoid of matter. The word is derived from the Latin adjective ''vacuus'' for "vacant" or " void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressure. Physicists often di ...

environments.

NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the US federal government responsible for the civil List of government space agencies, space program ...

and

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maintain lists of materials with low-outgassing properties suitable for use in 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 lightweight molecules to interfere with industrial or scientific vacuum processes. Moisture, sealants, lubricants, and adhesives are the most common sources, but even metals and glasses can release gases from cracks or impurities. The rate of outgassing increases at higher temperatures because the vapor 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 of surfaces, or heating of individual components or the entire assembly (a process called "bake-out") can drive off Volatility (chemistry), volatiles. NASA's Stardust (spacecraft), ''Stardust'' space probe suffere
reduced image quality
due to an unknown contaminant that had condensed on the charge-coupled device, CCD sensor of the navigation camera. A similar problem affected the Cassini–Huygens, ''Cassini'' space probe'
Narrow Angle Camera
but was corrected by repeatedly heating the system to 4 Celsius, °C. A comprehensive characterisation of outgassing effects using Mass spectrometry, mass spectrometers could be obtained for ESA's Rosetta (spacecraft), ''Rosetta'' spacecraft. Natural outgassing is commonplace in comets.

From rock

Outgassing is a possible source of many tenuous celestial body atmosphere, atmospheres of terrestrial planets or moons. Many materials are volatile relative to the extreme vacuum of Outer space, outer space, and may evaporate or even boil at ambient temperature. Materials on the lunar surface have completely outgassed and been blown away by solar winds long ago, but volatile materials may remain at depth. The atmosphere of the Moon, lunar atmosphere probably originates from outgassing of warm material below the surface. Once released, gases almost always are less density, dense than the surrounding rock (geology), rocks and sand and seep toward the surface. Explosive eruption, Explosive eruptions of volcanoes result from water or other volatiles outgassed from magma being trapped, for example by a lava dome. At the Earth's divergent boundary, tectonic divergent boundaries where new crust (geology), crust is being created, helium and carbon dioxide are some of the volatiles being outgassed from mantle (geology), mantle magma. Alpha decay of primordial 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

Outgassing can be significant if it collects in a closed environment where air is stagnant or recirculated. For example, new car smell consists 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 that plasticizers and solvents released from many industrial products, especially plastics, may be harmful to human health. Long-term exposure to solvent vapors can cause chronic solvent-induced encephalopathy (CSE). Outgassing toxic gases are of great concern in the design of submarines and space stations, which must have self-contained recirculated atmospheres.

In construction

The outgassing of small pockets of air near the surface of setting concrete can lead to permanent holes in the structure (called bugholes) that may compromise its structural integrity.

References

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