Utgassing

Utgassing is a term rarely used in formal literature and more commonly regarded as a misspelling or variant of outgassing. Outgassing refers to the release of gases that are absorbed, adsorbed, or trapped within a material, particularly under vacuum or elevated temperatures. In vacuum technology and spacecraft engineering, outgassing can contaminate surfaces and degrade vacuum quality.

The release occurs when volatile species, such as water vapor, solvents, or hydrogen, desorb from materials. Mechanisms include physical desorption, diffusion-driven release from the bulk, and chemical desorption. The rate and total amount of outgassed gas depend on material composition, surface area, temperature history, and prior exposure to air or solvents. Polymers, epoxies, adhesives, coatings, and lubricants typically contribute more significantly than metals.

Outgassing is measured by the outgassing rate, often expressed as a rate per unit area (for example, Torr·L·s⁻¹·cm⁻²) or as a total gas load in a chamber. In practice, the rate is determined using techniques such as rate-of-rise measurements after sealing a vacuum chamber or by residual gas analysis. The consequences of outgassing include elevated base pressures, surface contamination, and degraded performance of sensitive instruments like electron microscopes or optical sensors.

Mitigation focuses on material selection and processing. Strategies include using low-outgassing materials, thorough cleaning, and bake-out or thermal conditioning to desorb volatiles before assembly. Storage and assembly in clean or inert environments reduce ingress of moisture and solvents. Standards and specifications from space agencies and vacuum equipment manufacturers guide acceptable outgassing levels for specific applications.

See also: vacuum technology, desorption, bake-out, surface contamination.