Desorption Release
Release of trapped water vapor from non-metallic materials occurs when exposed to a vacuum or high-temperature environment. Outgassing outgassed moisture introduces gaseous water into the cleanroom or vacuum chamber, which can condense on cold optical surfaces. This phenomenon degrades the performance of spaceborne sensors and semiconductor manufacturing equipment.
It is quantified by measuring the total mass loss of the material over time.
Desorption Process
Water molecules are absorbed into the bulk of polymers and elastomers during storage in humid environments. Under vacuum conditions, these molecules diffuse to the surface and desorb into the surrounding space. The rate of this migration depends on the temperature and the diffusion coefficient of the material, with higher temperatures accelerating the release of the trapped water.
This outgassing behavior is particularly problematic in multi-layer insulation blankets and adhesive layers. These materials must undergo a thermal bake-out procedure prior to deployment to remove the majority of the volatile moisture.
Measurement System
Analytical instruments measure the release rate by monitoring the pressure rise in a sealed test chamber at a constant temperature. A quartz crystal microbalance can be positioned near the sample to measure the rate at which the outgassing outgassed moisture condenses on a cooled substrate. This setup allows researchers to distinguish between water vapor and other volatile organic compounds.
These measurements are compared against industry standard limits to qualify materials for space flight applications.
Contamination Effect
Condensation of water vapor on sensitive optical windows or mirrors scatters light and reduces transmission efficiency. In high-voltage equipment, this moisture can cause electrical arcing and component failure. These failures are avoided by selecting low-outgassing materials that have been certified through standardized testing.
