Outgassing

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Outgassing (sometimes called offgassing, particularly when in reference to indoor air quality) is the release of a gas that was dissolved, trapped, frozen, or absorbed in some material. [1] Outgassing can include sublimation and evaporation (which are phase transitions of a substance into a gas), as well as desorption, seepage from cracks or internal volumes, and gaseous products of slow chemical reactions. Boiling is generally thought of as a separate phenomenon from outgassing because it consists of a phase transition of a liquid into a vapor of the same substance.

Contents

In a vacuum

Outgassing is a challenge to creating and maintaining clean high-vacuum environments. NASA and ESA 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 volatiles.

NASA's Stardust space probe suffered reduced image quality due to an unknown contaminant that had condensed on the CCD sensor of the navigation camera. [2] A similar problem affected the Cassini space probe's Narrow Angle Camera, but was corrected by repeatedly heating the system to 4 °C. [3] A comprehensive characterisation of outgassing effects using mass spectrometers could be obtained for ESA's Rosetta spacecraft. [4]

Natural outgassing is commonplace in comets. [5]

From rock

Outgassing is a possible source of many tenuous atmospheres of terrestrial planets or moons. [6] Many materials are volatile relative to the extreme vacuum of 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 lunar atmosphere probably originates from outgassing of warm material below the surface.

Once released, gases almost always are less dense than the surrounding rocks and sand and seep toward the surface. 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 tectonic divergent boundaries where new crust is being created, helium and carbon dioxide are some of the volatiles being outgassed from 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. [7] 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. [8] [9]

See also

Related Research Articles

<span class="mw-page-title-main">Comet</span> Natural object in space that releases gas

A comet is an icy, small Solar System body that warms and begins to release gases when passing close to the Sun, a process called outgassing. This produces an extended, gravitationally unbound atmosphere or coma surrounding the nucleus, and sometimes a tail of gas and dust gas blown out from the coma. These phenomena are due to the effects of solar radiation and the outstreaming solar wind plasma acting upon the nucleus of the comet. Comet nuclei range from a few hundred meters to tens of kilometers across and are composed of loose collections of ice, dust, and small rocky particles. The coma may be up to 15 times Earth's diameter, while the tail may stretch beyond one astronomical unit. If sufficiently close and bright, a comet may be seen from Earth without the aid of a telescope and can subtend an arc of up to 30° across the sky. Comets have been observed and recorded since ancient times by many cultures and religions.

<span class="mw-page-title-main">Atmospheric entry</span> Passage of an object through the gases of an atmosphere from outer space

Atmospheric entry is the movement of an object from outer space into and through the gases of an atmosphere of a planet, dwarf planet, or natural satellite. There are two main types of atmospheric entry: uncontrolled entry, such as the entry of astronomical objects, space debris, or bolides; and controlled entry of a spacecraft capable of being navigated or following a predetermined course. Technologies and procedures allowing the controlled atmospheric entry, descent, and landing of spacecraft are collectively termed as EDL.

<i>Giotto</i> (spacecraft) European mission to comets Halley and Grigg–Skjellerup (1985–1992)

Giotto was a European robotic spacecraft mission from the European Space Agency. The spacecraft flew by and studied Halley's Comet and in doing so became the first spacecraft to make close up observations of a comet. On 13 March 1986, the spacecraft succeeded in approaching Halley's nucleus at a distance of 596 kilometers. It was named after the Early Italian Renaissance painter Giotto di Bondone. He had observed Halley's Comet in 1301 and was inspired to depict it as the star of Bethlehem in his painting Adoration of the Magi in the Scrovegni Chapel.

<i>Rosetta</i> (spacecraft) European mission to study Comet 67P/Churyumov-Gerasimenko (2004–2016)

Rosetta was a space probe built by the European Space Agency launched on 2 March 2004. Along with Philae, its lander module, Rosetta performed a detailed study of comet 67P/Churyumov–Gerasimenko (67P). During its journey to the comet, the spacecraft performed flybys of Earth, Mars, and the asteroids 21 Lutetia and 2867 Šteins. It was launched as the third cornerstone mission of the ESA's Horizon 2000 programme, after SOHO / Cluster and XMM-Newton.

<i>Huygens</i> (spacecraft) European reconnaissance lander sent to Saturns moon Titan

Huygens was an atmospheric entry robotic space probe that landed successfully on Saturn's moon Titan in 2005. Built and operated by the European Space Agency (ESA), launched by NASA, it was part of the Cassini–Huygens mission and became the first spacecraft to land on Titan and the farthest landing from Earth a spacecraft has ever made. The probe was named after the 17th-century Dutch astronomer Christiaan Huygens, who discovered Titan in 1655.

<i>Stardust</i> (spacecraft) NASA sample-return mission to Comet 81P/Wild 2 (1999–2011)

Stardust was a 385-kilogram robotic space probe launched by NASA on 7 February 1999. Its primary mission was to collect dust samples from the coma of comet Wild 2, as well as samples of cosmic dust, and return them to Earth for analysis. It was the first sample return mission of its kind. En route to Comet Wild 2, it also flew by and studied the asteroid 5535 Annefrank. The primary mission was successfully completed on 15 January 2006 when the sample return capsule returned to Earth.

<span class="mw-page-title-main">Spitzer Space Telescope</span> Infrared space telescope (2003–2020)

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<span class="mw-page-title-main">Space manufacturing</span> Production of manufactured goods in an environment outside a planetary atmosphere

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<span class="mw-page-title-main">Cosmic dust</span> Dust floating in space

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<span class="mw-page-title-main">Comet nucleus</span> Central part of a comet

The nucleus is the solid, central part of a comet, formerly termed a dirty snowball or an icy dirtball. A cometary nucleus is composed of rock, dust, and frozen gases. When heated by the Sun, the gases sublime and produce an atmosphere surrounding the nucleus known as the coma. The force exerted on the coma by the Sun's radiation pressure and solar wind cause an enormous tail to form, which points away from the Sun. A typical comet nucleus has an albedo of 0.04. This is blacker than coal, and may be caused by a covering of dust.

<span class="mw-page-title-main">Atmosphere of the Moon</span> Very scant presence of gases around the Moon

The atmosphere of the Moon is a very sparse layer of gases surrounding the Moon. For most practical purposes, the Moon is considered to be surrounded by vacuum. The elevated presence of atomic and molecular particles in its vicinity compared to interplanetary medium, referred to as "lunar atmosphere" for scientific objectives, is negligible in comparison with the gaseous envelopes surrounding Earth and most planets of the Solar System. The pressure of this small mass is around 3×10−15 atm (0.3 nPa), varying throughout the day, and in total mass less than 10 metric tonnes. Otherwise, the Moon is considered not to have an atmosphere because it cannot absorb measurable quantities of radiation, does not appear layered or self-circulating, and requires constant replenishment due to the high rate at which its gases are lost into space.

<span class="mw-page-title-main">Exploration of Jupiter</span> Overview of the exploration of Jupiter the planet and its moons

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<span class="mw-page-title-main">Extinct comet</span> Comet that lacks typical activity

An extinct comet is a comet that has expelled most of its volatile ice and has little left to form a tail and coma. In a dormant comet, rather than being depleted, any remaining volatile components have been sealed beneath an inactive surface layer.

<span class="mw-page-title-main">Comet tail</span> Dust or gases blown off a comet by solar wind in the inner solar system, leaving a visible trail

A comet tail and coma are visible features of a comet when they are illuminated by the Sun and may become visible from Earth when a comet passes through the inner Solar System. As a comet approaches the inner Solar System, solar radiation causes the volatile materials within the comet to vaporize and stream out of the nucleus, carrying dust away with them.

<span class="mw-page-title-main">Materials for use in vacuum</span>

Materials for use in vacuum are materials that show very low rates of outgassing in vacuum and, where applicable, are tolerant to bake-out temperatures. The requirements grow increasingly stringent with the desired degree of vacuum to be achieved in the vacuum chamber. The materials can produce gas by several mechanisms. Molecules of gases and water can be adsorbed on the material surface. Materials may sublimate in vacuum. Or the gases can be released from porous materials or from cracks and crevices. Traces of lubricants, residues from machining, can be present on the surfaces. A specific risk is outgassing of solvents absorbed in plastics after cleaning.

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References

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