Outgassing

Under gassing refers to the escape of gases from the liquid or solid material. This can be done due to the pressure relief, elevated temperature, or other processes, such as bacterial or chemical conversion.

Outgassing is a common process in nature. Technically, it can be either required, for example during curing of adhesive bonds, but also undesirable, for example in landfill sites. If the gases are selectively removed by a technical process, we speak mostly of degassing.

Physical Basics

Outgassing occurs most in a warming liquids in combination with a pressure reduction and is determined here by the solubility of the gases. This decreases according to Henry's law with decreasing partial pressure and rising temperatures. A well-known from everyday form of outgassing is foaming when opening a bottle of soda water with carbonic acid.

In solids, the gas molecules first have to diffuse to the surface and then desorptieren from there, and therefore the degassing takes much longer than of solids from liquids. By increasing the temperature the rate of gas release increases exponentially.

Pores, resulting in a natural way ( pumice ) and artificial ( foam ), simplify the gas tax.

Outgassing by volcanism

A clear example is the outgassing at solidifying lava from volcanoes, especially in the highly viscous forms ( aa- lava ) of the Indian and Pacific volcanic islands. The outgassing of sulfur-containing substances can usually clearly smell.

On the ascent of magma through a volcanic vent, it also comes to such a strong outgassing by pressure relief that entrained rock fragments are accelerated up to supersonic speed.

Certainly a part of the origin of terrestrial water through water vapor can be explained, which is outgassed in the course of the earth from the earth. A larger part is likely to come from the previous impacts of comets, meteors and asteroids from the distant reaches of the solar system. Thus, many carbonaceous chondrites in the outer asteroid belt on a water or ice content of more than 10 % of their mass.

Outgassing as astrophysical phenomenon

A well-known example of the outgassing are the nuclei of tail forming comet when they are heated by the solar radiation in the near- sun- web sections of their elongated ellipses. In this approach almost everyone dismisses this "dirty snowballs " of rock and ice, various gases and particulate matter on its surface, which envelop the rock core as luminous coma, or envelope and be " blown " by the solar wind and radiation pressure as a thin tail of a comet into space.

Also, most Trans Neptune contain water and other ice that is at possible path changes towards the sun or in larger meteorite impacts to water vapor or other gas.

A medical phenomenon

When sudden drop in pressure on the human body, for example by too rapid ascent of a diver, there may be a bubble formation in the blood with serious medical consequences, the so-called decompression sickness, come.

Outgassing in the art

In the home and industry is important to avoid the outgassing of toxic substances, such as paints, from wall and floor coverings, treated wood or textiles. In the 1990s it was discovered that formaldehyde-containing materials, for example in impregnated wood materials, harmful substances outgas. Also, certain urea compounds can release partly for years to formaldehyde in the ambient air.

To avoid contamination of the breathing air of enclosed spaces by pollutants, it has changed many production methods as for furniture, paints, adhesives and wall coverings. It was possible to reduce the released pollutants by up to 90% at Verfliesungen and sealers.

However, there are no materials that do entirely without emissions. Also, upholstered furniture or mattresses made ​​of natural products such as coconut or sheep's wool can outgas toxic pesticides. In contrast, gases in coatings with oils, in waxes or lyes even organic solvents such as terpenes, but this must not be harmful.

In vacuum technology, the outgassing of materials used, a problem because in the vacuum following on closes gas again leads to an increase in pressure and the achievable vacuum limited ( so-called virtual leak).