Permeability Measurements

In typical permeability experiments, a disk sample is sealed gas tight over a support tube. A gas or gas mixture is supplied to one side, and one or more species permeate to the other side, where a sweep gas and/or pump collect the gas. The modes of operation are numerous, and so are the ways to analyze the permeation, including gas chromatography (GC) and mass spectroscopy (MS). Typically, an inert gas added to the entry side gas mixture is used for monitoring the presence or absence of background leakage through seal leaks or sample cracks and porosity.

 

In general, a large sample area or tubular sample is preferable, as it reduces the relative effects of leakage from seal ring and general equipment. It also simplifies the considerations of sample geometry for samples where the thickness is not much smaller than the diameter so that permeation from the side is significant. However, a large sample may put higher requirements to the mechanical assembly and seal.

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