Outgassing Measurement
Mass transfer rate of trapped gas molecules escaping from the interior of a solid material defines the base stability of vacuum-exposed sensor housings. This bulk desorption flux determines the long-term outgassing rate that can degrade the performance of hermetically sealed cavities or ultra-high vacuum instruments. The measurement represents the molecular quantity passing through a unit surface area per unit of time.
Transport Mechanism
Internal diffusion dominates the rate of gas release once surface-adsorbed species have been evacuated. Molecules migrate through the lattice or grain boundaries of metals and polymers to reach the surface where they escape into the surrounding environment. This migration is highly temperature-dependent and increases exponentially as the system warms up.
Sensor Influence
Thermal drift and pressure variations in sensor cavities often trace back to this slow release of entrapped moisture or hydrocarbons. In resonant micro-sensors, bulk desorption flux alters the internal pressure of the cavity, leading to changes in the quality factor and a shift in the resonant frequency over time. High-precision capacitive gauges similarly experience drift when outgassed molecules accumulate on active surfaces, which alters the dielectric constant and degrades the reference baseline.
This phenomenon is particularly challenging in sealed packages that cannot be recalibrated after installation.
Mitigation Strategy
Baking components under high vacuum before final assembly accelerates the release of volatile species to reduce subsequent outgassing. Applying barrier coatings such as alumina via atomic layer deposition also restricts the path of migrating molecules. Choosing low-outgassing materials like specialized fluoroelastomers or glass-ceramic seals ensures the cavity maintains its pressure limits over its operating life.
