Argon for surface and pore characterisation
The critically reviewed IUPAC report “Physisorption of gases, with special reference to the evaluation of surface area and pore size distribution” was published in 2015 and is an up-to-date compendium for the characterization of porous materials using gas sorption. Besides an extended isotherm classification, this updated release includes numerous recommendations for the measurement and interpretation of isotherm data. “New recommendations” that have been the basis of applying our measurement methods since many years. A fact that becomes obvious in this central topic is that the characterization of micropores using physisorption of should be carried out with argon at a temperature of 87 K (boiling temperature of argon). We have identified this advantage more than 20 years ago and its practical realization to achieve 87 K was by use of liquid argon for a long time.
More recently, we started to equip our instruments with so-called cryoTune modules, an option that was specifically designed for achieving an 82 – 135 K temperature range. In this way, not only the boiling point of the noble gas argon at 87 K, but also the boiling point of the noble gas krypton at 120 K becomes viable for isotherm analysis. This article describes these additional research options with a critical discussion of the nitrogen-based results as traditional basis not only for pore size but also for surface area determination.
