Deviation from the inverse-thickness relation in gas-metal permeation



The permeation rate of hydrogen through cylindrical membranes of type 321 stainless steel was determined under a wide range of conditions. The pressure was varied from 0.1 to 30.0 atm. and the temperature from 300° to 800°C. Four permeation membranes were used with wall thicknesses of 0.0252, 0.1003, 0.1011, and 0.2475 cm.

The permeation rate was found to deviate from the square-root-of-pressure and inverse-thickness relations predicted by the Richardson equation. Slow surface reactions are considered to be the cause of the observed deviations. The permeation data were correlated by a semiempirical interfacial resistance model.

Permeation rates were observed to increase with time of membrane exposure to hydrogen. It is believed this resulted from changing surface activity.