Errors due to zero uncertainties and buoyancy in the gravimetric measurements of sorption isotherms

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Abstract
Besides the influences of Knudsen forces and convection which are due to thermal gas flow, a zero shift during cooling down of the sample in vacuo may seriously affect the measurement of adsorption isotherms at low temperatures. This applies especially to the measurement of nitrogen isotherms at 77 K for surface area and pore size determination. Microporous samples present difficulties in determining the necessary buoyancy corrections for the sample itself; in addition, the buoyancy of the adsorbed layers has to be taken into account.