ИСТИНА

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 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. In studies of glass surface and films on glass the main attention is often paid to chemistry of surface and near the surface region. The problems of morphology and geometrical structure of surface are mainly staying in the shadow. The availability of macro-, meso- and micropores in a solid or on its surface affects adsorptive, adhesive, mechanical, capillary and other properties of this system. In accordance with the IUPAC classification(1) the pores in solids are subdivided into macro- (with mean diameter larger than 50 nm), meso- (2–50 nm) and micropores (less than 2 nm). Nanoporosity is understood as the pores of nano-size and includes micro- and mesopores. The common adsorption methods based on the analysis of adsorption-desorption isotherms with hysteresis loop in capillary condensation region as well as mercury penetration porometry can be used for diagnostics meso- and macropores. For some types of adsorbents containing micropores only it is possible to relate the equilibrium adsorption parameters to the micropore diameters. And although the additional information on nanoporous morphology of glass surface can be drawn by NMR, neutron scattering, X-ray scattering and a. o., the quantitative methods for researching microporosity are not developed. The problem of the pore morphology diagnostics becomes almost insoluble if micro- and mesopores are present simultaneously or the volume of nanopores is small.