Changing the relation between micro- and mesoporosity in porous glasses: The effect of different factors

Abstract

The relation between micro- and mesoporosity in the porous glasses produced by leaching of two-phase alkali borosilicate glasses was studied by use of advanced classical nitrogen equilibrium adsorption–desorption methods and new kinetic method of diffusion diagnostics with mass spectral recording. The effect of different factors, such as chemical composition, conditions of acid and alkaline treatments on the change of morphology and pore characteristics of the micro- and mesoporous substructures in the porous glasses was revealed. The porous glasses are characterized by the polymodal size distribution of mesopores (up to 4 modes) and micropores (up to 3 modes). The shape of mesopores is not purely cylindrical; there is a contribution of conical and interglobular pores. The micropore volume decreases with the decrease of the mesopore specific surface area and increasing the globule diameters of secondary silica. The micropores in the porous glasses are generally the regions of interglobular contacts in secondary silica with 1–2 times the diameter of N2 molecules. The introducing lead oxide allows obtaining the porous glasses with the highest specific surface area, maximum micropore volume, and minimum micropore diameter. The introduction of phosphorus and fluorine in the glass matrix allows producing the porous glasses with the minimal porosity, mesopore surface area, micropore volume and with the maximal size of mesopores. When increasing the leaching concentration of hydrochloric acid from 1 to 3M and acid leaching time from 3 to 9h, the mesopore specific surface area decreases and the mesopore diameters increase. The effect of alkali leads to the monomodal pore size distribution of mesopores, significant increase in the mesopore volume, and significant reduction in the micropore volume. At this, the new micropores due to the dissolution of channel walls do not create.