1.1 This guide covers the measurement of gas permeability and gas diffusivity of carbons and graphite. Two techniques are discussed, the static equilibrium method, an integrated method capable of measuring both gas permeability and gas diffusivity, and the vacuum leak method, which measures the gas permeability of the specimen.

1.2 Both of the gas permeability techniques discussed assume laminar flow through the pores of the specimen. For the purposes of analysis, it is assumed that the resultant gas permeability consists of viscous flow (pressure driven gas flow) and slip (the interaction of gas molecules with the walls of the pores). Generally, the contribution from slip is much smaller than that from viscous flow but can be significant in cases of low permeable flow and specimens with very fine pore sizes.

1.3 Gas permeability measurements are discussed for the vacuum leak method at mean pressures up to 50 kPa and differential pressures in the range 5 kPa to 50 kPa.

1.4 Gas permeability measurements are discussed for the static equilibrium method at a mean pressure of 100 kPa and differential pressures in the range of 0.01 kPa to 0.15 kPa. Gas diffusivity measurements are also discussed for the static equilibrium method under the same conditions detailed in 1.4.

1.5 This guide is based on experiments conducted on small specimens between 12Ø × 20 mm and 19Ø × 55 mm, but the test methods may be suitable for other sizes. Should the testing of specimens outside of this geometry be required, the user will need to undertake testing to confirm the techniques are suitable. Viscous coefficients in the range from 0.5 × 10^-10 cm² to 200.0 × 10^-10 cm² are readily measurable by the discussed test methods. Gas diffusivity ratios in the range of 0.001 to 0.5 are readily measurable by the static equilibrium method. The measurements and analysis from which this guide has been derived have been published as an ASTM technical paper.2

1.6 Units—The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.7 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

1.8 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.