New apparatus for measuring surface areas as low as 0.1 cm2

Abstract

An apparatus is described which permits accurate determination of gas adsorption of solids having lower adsorptive capacity. Conventional measurement of gas uptake by solids having surface areas less than 1 m2 is not generally feasible at subatmospheric pressure. The small pressure drop due to adsorption is easily lost in the noise created by ambient temperature fluctuations. Possible experimental errors in the volumetric measurement of gas uptake due to temperature fluctuations were greatly reduced by using an apparatus whose reference and sample adsorption cells are disposed in a lateral symmetry. The apparatus consists of a differential micromanometer whose two arms are connected in a lateral symmetry to a pair of sample and reference burets of nearly equal volume for dosing gas into sample and reference cells also of nearly equal volume. When the two cells are immersed in the same temperature bath this design greatly reduces measurement uncertainties due to fluctuations in the temperature. Surface areas as small as 300, 1 and 0.1 cm2 were measured through volumetric gas uptakes of nitrogen at 78 K, krypton at 78 K and xenon at 90 K, respectively.