V.A. Kreisberg, V.P. Rakcheev, T.V. Antropova
Physics and Chemistry of Glasses, (2002) (in print)
ABSTRACT. Some samples of porous glasses with various nanoporous structure produced by the leaching of alkali borosilicate glasses were investigated by the new method of diffusion diagnostics of micro porosity of solids and films. The method is based on very sensitive registration of desorbing gases using desorption kinetic mass spectrometry. The proposed kinetic desorption method does not diagnose macropores thus allowing to study micropores in the presence of macropores. Mean pore diameter, pore size distribution and volume of micropores can be detected from diffusionыtransport characteristics of nanoporous structure. The analysis of kinetic curves of nitrogen, oxygen and argon desorption at 77.5 K detected the trimodal structure of pores. Nanoporous structure of the porous glasses consists essentially of transporting mesopores with mean diameter from 3.8 to 10.3 nm and two kinds of adsorbing micropores diameter of which was estimated to be equal to about 0.4 and 0.6-0.7 nm what corresponds one-two diameters of gas molecules. The trimodal pore-size distribution was built with regards to the correlation detected between mean pore diameter and gas conductivity and gas diffusion coefficient. Diffusion coefficients of nitrogen, oxygen and argon at 77.5 K for each kind of pores were calculated using diffusion equations for spherical symmetry. The use of different gas diffusing molecules allowed to estimate the influence of shape, size and value of quadrupole moment of the molecules on the diffusion-transport characteristics of porous glasses.