Outgassing

Outgassing is the release of gases that were dissolved, absorbed, or trapped in a solid or liquid, often occurring when a material is placed in a vacuum or very low-pressure environment. In geology and planetary science, the term can refer to gases released from rocks or other materials as conditions change, such as during heating or decompression. In engineering, outgassing is most commonly discussed in the context of materials used in vacuum environments, including spacecraft, satellites, and high-vacuum instruments.

In materials used for space and vacuum systems, many polymers, resins, adhesives, coatings, and lubricants contain volatile components. When these materials are exposed to vacuum or elevated temperatures, the volatiles can desorb and escape as gases. Outgassing is typically categorized as primary (release of volatiles originally present in the material) and secondary (release of gases that were absorbed or adsorbed and are released as the material is heated or placed in vacuum).

Implications of outgassing include contamination of optical surfaces, sensors, and vacuum seals, potential deposition of films on critical components, and changes to pressure within a system. To mitigate these effects, engineers perform material selection with low outgassing properties, pre-bake-out or vacuum bake-out of components, cleaning, and proper venting during assembly. Outgassing is often quantified using standard tests that measure parameters such as total mass loss and condensable volatile materials, allowing materials to be rated for use in vacuum environments.