The Kelvin equation

The capillary condensation/evaporation process is studied in conjunction with small angle X-ray scattering measurements. The scattering data are analyzed with the indirect Fourier transformation technique and the results are compared with the predictions of the Kelvin equation. It is found that the Kelvin equation is obeyed by menisci with mean radius of curvature as low as 40 Å. For smaller radii, in particular from 40 to 30 Å, the two methods differ by ∼25%. Broekhoff and de Boer analysis may improve the prediction. The hysteresis region of an adsorption step is presented schematically.

The predictions of the Kelvin/Cohan equation are compared with small angle X-ray scattering data that have been analyzed with the indirect Fourier transformation method. It is found that the two methods are in agreement when the mean radius of curvature is as low as 40 Å. For smaller radii, in particular from 40 to 30 Å, the two methods differ by ∼25%.Figure optionsDownload as PowerPoint slide