This paper reports on the results of an investigation into the influence of the addition of a KCl salt to an HCl acid solution on the leaching kinetics of two-phase sodium borosilicate glasses and on the structural parameters of the leaching products (porous glasses). The contributions from different molecular species of silica to its total amount in leaching solutions are evaluated using the kinetic spectrophotometric technique for determining silicon in the form of β -silicomolybdic heteropoly acid. It is revealed that the addition of the salt to the leaching acid solution leads to a fast polymerization process with the formation of weakly structurized silica gel.

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This work is devoted to the investigation into the influence of the composition of the initial two-phase alkali borosilicate glass and a leaching solution on the pore structure in nanoporous glasses, which are promising materials for use in optical, laser, and lab-on-chip technologies. It is known that the structure of nanoporous glasses is determined by the distribution of secondary silica inside channels in the high-silica network formed upon chemical dissolution of components of the unstable phase of the alkali borosilicate glass [1]. The main factors that affect the distribution of secondary silica are the composition of the initial alkali borosilicate glass and leaching conditions, such as the temperature, composition, concentration, and pH of the acid solution. In our previous papers [2,3], it was shown that the presence of potassium chloride in the acid leaching solution leads to a rapid polymerization with the formation of weakly structured silica, which affects the packing of secondary silica. SAMPLE PREPARATION AND EXPERIMENTAL TECHNIQUETwo-phase alkali borosilicate glasses of three compositions (Table 1) were leached in 3 M HCl solutions with addition of 10 wt % KCl and without it. Glass samples in the form of polished disks 34.5 mm in diameter and 2 mm in thickness were suspended (immersed) by a platinum wire in acid solutions and leached without stirring in the course of boiling. The initial ratio of the glass surface area to the solution volume was 0.04 cm -1 , which provided a constant pH value of the solution during the experiment.In the solutions formed after through acid leaching of the samples, the kinetics of complex reactions with 1 This paper was presented at the Topical Meeting of the European Ceramic Society "Structural Chemistry of Partially Ordered Systems, Nanoparticles, and Nanocomposites," St. Petersburg, Russia, June 27-29, 2006. the participation of silica passed from the unstable phase of the glass into the solution was investigated according to the procedure described in [3,4]. The contribution from different molecular forms of silica to the total amount of this component in the solution was determined from the results of the kinetic spectrophotometric analysis for the presence of silicon in the form of β -silicomolybdic heteropoly acid (the error in the determination of the silicon content was ± 0.1 [5]). After through leaching of the glasses, the samples of the nanoporous glass obtained were washed in distilled water at room temperature and dried at a temperature of 120 ° C for 1 h.The structure of porous glasses was investigated using the adsorption method [6, pp. 72-75]. The mean radius r of the pores, their relative volume V , and specific surface area S s p were calculated from the water vapor adsorption-desorption isotherms measured at a temperature of 15 ° C. The relative error in the determination of these parameters did not exceed ± 2% (for the relative volume V ) and ± 10% (for the mean radius r and the specific surface area S sp ) [7, p. 114].The structural paramete...

The possibility of controlling the content and ratio of Brønsted acid to Lewis base centers on the surface of high-silica porous glass (PG) with various compositions based on two-phase alkali-borosilicate glass by varying the conditions of the preparation of PG during the acid work-up of the initial glass is shown. The results demonstrate the possibility to control the features of the surface of the PG, and in particular, the ratio of silanol to siloxane structures.