Small-angle X-ray scattering studies of adsorption in Vycor glass

摘要

Porous Vycor is examined by measuring CH_2Br_2 adsorption in situ with small-angle X-ray scattering. When a class of pores fills with condensed vapors of this particular adsorbate it ceases to act as scatterer and only the remaining empty pores produce a measurable intensity. By determining a number of scattering curves at various relative pressure loadings details on the structure of the glass as well as on the adsorption/desorption mechanism are obtained. Pore chord length and specific surface area are estimated from Porod tangent analysis to 78 ? and 108 m~2/g. Comparison of the results with those reported for N_2 and Ar adsorption is also given. The role of network effects on the shape of the hysteresis loop is considered and the pore-blocking hypothesis is verified from the scattering spectra. The pore connectivity is calculated to 5.6. The X-ray data are further treated with the inverse Fourier transformation technique. Pore-size distributions are extracted and weighed against the prediction of the Kelvin equation.