Automated Xe adsorption technique to measure small Brunauer–Emmett–Teller surface area of several square centimeters

Abstract

An automated Xe adsorption apparatus has been developed that enables the measurement of a Brunauer–Emmett–Teller (BET) surface area of several cm2 with a repeatability of 4% (standard deviation). The apparatus is equipped with a differential type capacitance manometer, each hand of which is connected to a sample and reference adsorption cell having a symmetrical design, that is the temperature-compensated volumetric system which was reported by one of the authors [I. Suzuki, Rev. Sci. Instrum. 53, 1061 (1982); ibid., 66, 5070 (1995); ibid., 68, 4531 (1998)]. All procedures for measuring gas adsorption are computer controlled, and the coolant meniscus height is also computer controlled to keep the adsorption cell volume constant. A specially polished Si crystal rod was adopted as the standard sample. The BET surface area of the standard sample was measured by both the original temperature-compensated system and the newly developed automated system. Obtained results are fully consistent. We propose the adsorption cross section of Xe to be 0.25 nm2 based on our measurements. In addition, we demonstrate a series of experimental results which show a quantitative correlation between the capacitance and surface microroughness of a capacitor with rugged surface electrode.