The Surface Structure of Silica Gel Studied by Dielectric Dispersion

Abstract

The effect of water adsorption and heat treatment at various temperatures between 200 and 1100°C on the dielectric dispersions of silica gel was measured in the frequency range from 50 to 3×106 Hz and 9.81 GHz and in the temperature range from −196°C to 180°C. Two anomalous dispersions (Dispersion I and II) and one anomaly (Anomaly III) were found. The mechanisms of those anomalies were discussed in relation to some physical properties and silica crystal structures. Dispersion I, having activation energy ΔE equal to 11 to 14 kcal/mol, can be ascribed to the monomolecular layer of adsorbed water. Dispersion II, with activation energy of about 5 to 7 kcal/mol, can be attributed to proton diffusion through hydrogen-bond chain of surface silanol groups. Anomaly III, having activation energy of about 3 kcal/mol, may be assigned to dipolar rotation of free silanol.

Cause of the fragile-to-strong transition observed in water confined in C-S-H gel

“…65 Such an interpretation is furthermore consistent with an earlier study on high temperature treated silica gel, where a fast process with similar activation energy was attributed to the rotation of surface bonded hydroxyl groups. 66 A similar result was also obtained for water in montmorillonite (hydrated clays) 67 and more recently in hydrated ordinary Portland cement where a decrease in the elastic intensity occurs at about 190 K and attributed to the activation of OH − motions. 68 In addition, studies on dried amorphous polysaccharides (cellulose and dextran) with two and three hydroxyl groups per ring, respectively, have shown on a weak relaxation similar to the here obtained process 1, however, with a somewhat higher activation energy of 0.33 eV.…”

DC dielectric study of polyethylene/CaCO3 composites

“…Dielectric studies of adsorbed water on inorganic surfaces and in porous systems [27][28][29][30][31][32][33][34][35] are also of relevance in this context. In all these cases, molecular and interfacial effects overlap.…”

Amino-Functionalized Urea–Formaldehyde Framework Mesoporous Silica for U(VI) Adsorption in Wastewater Treatment

“…Results were similar to that of mesoporous silicas SBA-15, which uses costly P123 as framework, respectively. Because mesoporous materials have a significant effect on the removal of heavy metal in aqueous solution, − the adsorbents used in this study were place in a complex solution environment. According to the experimental data, the removal ability of heavy metals in aqueous solution is not only related to electrostatic attraction, surface precipitation, and chemical interaction between the metal ions and the surface functional groups, but also related to its surface free energy − and its pore system.…”

“…16 This type of urea− formaldehyde framework mesoporous silica has a complex pore structure. To maintain the surface area 17 and a high surface activity, 18 urea−formaldehyde polymer/SiO 2 composite microspheres were heated gradually after attaching SiO 2 colloid onto the framework under strict temperature and pH conditions. Superpure high activity silica was obtained.…”