Precision Evaluation in Kr Adsorption for Small BET Surface Area Measurements of Less Than 1 m2

A volumetric Kr-adsorption apparatus using a precise capacitance manometer has been developed. A specially designed adsorption cell (CVC: constant volume adsorption cell) utilizing a vacuum jacket (Joyner et al., 1949) is adopted to keep the adsorption cell volume constant regardless of the variation in liquid nitrogen level throughout the experiment. Using the CVC, the pressure change in accordance with liquid N₂ supply cycle has been minimized to less than 0.01 Pa compare to about 1 Pa for conventional cell. Time dependent change of the adsorption cell volume and repeatability in its measurements have been demonstrated in detail using helium gas. Good linearity of the BET plot of the Kr adsorption isotherm on several hundred cm² samples are demonstrated in the relative pressure range from 0.05 to 0.35.