The effect of pressure modulation on the flow of gas through a solid membrane: Surface inhibition and internal traps

By permeation of a gaseous diffusant, pressure modulations may be transmitted through a solid foil from one experimental chamber to another. The resulting attenuation and phase lag of the transmitted modulation depend on all processes capable of influencing the diffusant flux. It is shown that diffusants which take part in surface reactions of finite rate or are subject to reversible trapping within the solid have a frequency response characteristic of the process involved. Mathematical separation of the bulk and surface processes is effected by a treatment which uses a separate matrix to describe each process and so is readily applied to the problem of multiply controlled flows. The analysis suggests that experimental separation of processes is possible even when both surface reaction and internal trapping have a part in determining rate of flow.