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What is the unit of gas transmission rate, gas permeability, and gas permeance?

Usually, the permeance (cm3/m2·24h·0.1MPa) and the gas transmission rate are the only things we are concerned about.

ASTM D1434 Test Standard

In ASTM D1434, there are three descriptions of permeability parameters:

1. Gas Transmission Rate (GTR): The quantity of a given gas passing through a unit of the parallel surfaces of a plastic film in unit time under the conditions of the test. The SI unit of GTR is 1 mol / (m2·s).

2. Permeance (P): The ratio of the gas transmission rate to the difference in partial pressure of the gas on the two sides of the film. The SI unit of permeance is 1 mol / (m2·s·Pa).

3. Permeability (P): The product of the permeance and the thickness of a film. The SI unit of P is 1 mol/(m2·s·Pa).

ISO 2556 Test Standard

There is only one description of the permeability parameter in ISO 2556:2001:

Gas Transmission Rate: The volume of gas which, under steady conditions, crosses a unit area of the sample in unit time under unit pressure difference and at constant temperature. The rate is usually expressed in cm3/m2·d·atm.

Through the analysis of the standard definition and result unit, in ASTM D1434-23 and ISO 2556:2001, the definitions of the gas permeability coefficient are the same; the expressions of the permeance are different, ASTM D1434 ’Permeance (P)’ = ISO 2556 ’Gas transmission rate’, the units could all be transformed to cm3/m2·24h·0.1MPa.

The gas permeability rate is the volume of the gas that passes through a unit area of specimen in a unit of time; it is determined by the barrier property of the material and the partial pressure difference between two sides of the specimen.

The gas permeability rate is determined by the test conditions and the specimen itself. The permeance is only determined by the specimen itself. As to the gas permeability coefficient, it is determined by the properties of the specimen material itself.

Usually, the permeance (cm3/m2·24h·0.1MPa) and the gas transmission rate are the only things we are concerned about.

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Posted in Product Knowledge on Sep 13, 2023.
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