Materials for use in vacuum

Materials for use in vacuum are materials that show very low rates of <a href="/facts/Outgassing/IgMX4wUP">outgassing</a> in <a href="/facts/Vacuum/BTk3goyV">vacuum</a> and, where applicable, are tolerant to <a href="/facts/Bake-out/QqovwzVr">bake-out</a> temperatures. The requirements grow increasingly stringent with the desired degree of vacuum to be achieved in the <a href="/facts/Vacuum_chamber/9LkgL4qm">vacuum chamber</a>.
The materials can produce gas by several mechanisms. Molecules of gases and water can be <a href="/facts/Adsorption/ARH9peYM">adsorbed</a> on the material surface (therefore materials with low affinity to water have to be chosen, which eliminates many plastics). Materials may <a href="/facts/Sublimation_(phase_transition)/KDoKokMn">sublimate</a> in vacuum (this includes some metals and their alloys, most notably cadmium and zinc). Or the gases can be released from <a href="/facts/Porosity/UoyAJU8X">porous</a> 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.
The gases liberated from the materials not only lower the vacuum quality, but also can be reabsorbed on other surfaces, creating deposits and contaminating the chamber.
Yet another problem is diffusion of gases through the materials themselves. Atmospheric <a href="/facts/Helium/yRul93TG">helium</a> can diffuse even through <a href="/facts/Pyrex/TsG4WXde">Pyrex</a> glass, even if slowly (and elevated temperatures above room temperature are generally needed); this however is usually not an issue. Some materials might also expand or increase in size causing problems in delicate equipment.
In addition to the gas-related issues, the materials have to maintain adequate strength through the entire required temperature range (sometimes reaching <a href="/facts/Cryogenic/cw7dHAkp">cryogenic</a> temperatures), maintain their properties (elasticity, plasticity, electrical and <a href="/facts/Thermal_conductivity/qWnSG3nQ">thermal conductivity</a> or lack of it, etc.), be machinable, and if possible not be overly expensive. Yet another concern is the <a href="/facts/Thermal_expansion_coefficient/BP2vjX0N">thermal expansion coefficient</a> match of adjacent parts.

Materials for use in vacuum open-in-new

Materials for use in vacuum