The surface properties of silica gels. I. Importance of pH in the preparation from sodium silicate and sulphuric acid

Abstract

Gels were prepared by adding sodium silicate solution to sulphuric acid until a certain pH was reached, and then the products were aged, washed and dried under controlled conditions. The surface properties of the dry gels were studied by measuring adsorption isotherms of nitrogen at – 195·8° and nitrous oxide at — 78·5°. The pH reached came within the range 3·7–5·8, as this corresponded to a decrease in setting time from over an hour to a few seconds. For gels prepared over this pH range, the isotherms of the two gases also changed profoundly, both sets showing the same general pattern. In one preparation the temperature was varied, and in another the ageing period was reduced to the minimum; in neither case could any difference in the adsorption of nitrous oxide be detected. Activation, by soaking in very dilute sulphuric acid, was shown to be more important for a gel prepared at the higher‐pH end of the range. Surface areas have been calculated from both sets of isotherms by the Brunauer, Emmett and Teller (B.E.T.) method. Good agreement is obtained, in some cases, by assuming that each nitrous oxide molecule occupies an area of 20·4 Å2 in the close‐packed monolayer, and taking the usual value of 16·2 Å2 for the nitrogen molecule. The values of residual water content and B.E.T. surface area both decreased substantially over the pH range, but there appears to be no simple relationship between them.

Flexible aerogels with interpenetrating network structure of bacterial cellulose–silica composite from sodium silicate precursor via freeze drying process

“…The gel time of sodium silicate is determined by the pH of sodium silicate, and the gel will form instantaneously if the pH of the solution is adjusted to a suitable range. 25,26 It was found that the clear sodium silicate solution (Fig. 2a) would be converted into milky gels (Fig.…”

“…25,26 It was found that the clear sodium silicate solution (Fig. 2a) would be converted into milky gels (Fig.…”

Structure-Directing Effect on Silica Nanoparticle Growth in Sodium Silicate Solutions through Small-Angle X-ray Scattering

“…However, a detailed understanding of the structure of sodium silicate with different SiO 2 /Na 2 O ratios is essential for the synthesis of silica nanoparticles. There have been some reports on the role of sodium silicate as a raw material in silica preparation. − However, precisely understanding the structure of the species in terms of particle shape and size distribution is challenging because the sol species are constantly changing, and it is difficult to obtain extensive, reliable, and quantitative data using ex situ experimental methods.…”