CHARACTERIZATION OF POROUS-GLASS BY ADSORPTION OF DIBROMOMETHANE IN CONJUNCTION WITH SMALL-ANGLE X-RAY-SCATTERING

Two porous glass samples of the Vycor type, one in a monolithic form a nd the other as a fine powder, were examined by the method of small-an gle x-ray scattering (SAXS). Adsorption isotherms of dibromomethane (C H2Br2) were measured on the same samples, and analyzed according to th e Kelvin equation. The SAXS measurements were repeated on samples that had been brought to equilibrium with known relative pressures (p/P-0) of CH2Br2, which has a similar electron density as Vycor. Analysis of the data, in terms of fractal geometry, was also accomplished. The fr actal dimension for the dry samples was estimated to be 2.5 +/- 0.1. F urthermore, as the adsorbate loading was increased defractalization wa s observed. Subsequently, the fractality in Vycor was estimated to hav e an upper cutoff limit equal to 15 Angstrom. A correlation between th e two methods was demonstrated, by reconstructing the adsorption isoth erm from the SAXS data, in two ways: first, by plotting the scattering intensities against p/p(0) andsecond by plotting the Pored slopes aga inst p/p(0).