Abstract
The most widely used method for surface-area determination is low-temperature gas adsorption, particularly nitrogen and krypton at liquid-nitrogen temperature. Most gases can and have been used, and these include water vapour at room temperature and carbon dioxide at room temperature and at -78°C. The problems that arise when one deviates from the standard conditions are: what is the applicable molecular area and what is the correct theoretical model to use? The first question is usually resolved by accepting published values or carrying out experiments to determine molecular area by comparison with nitrogen adsorption at liquid-nitrogen temperature. Since there is no unanimity in published data, the second procedure is probably preferable. The second question is usually resolved from an examination of the isotherm, the BET or the Langmuir equation being then used. When coverage is very low, as with carbon dioxide at room temperature, the Freundlich equation may be applicable.
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