The Influence of Surface Tension of Intrapore Fluid on the Structural and Surface Properties of Silicon Dioxide Obtained from Nepheline-Containing Raw Materials

The article presents the results of research on the effect of intrapore fluid surface tension on the structural and surface properties (specific surface area, pore volume, and pore size distribution) of silica (SiO₂) synthesized via the acid decomposition of nepheline mineral raw materials. The synthesized samples were analyzed using chemical and X-ray diffraction (XRD) methods, as well as the Brunauer–Emmett–Teller (BET) method for determining specific surface area and the Barrett–Joyner–Halenda (BJH) method for pore size distribution. Equations were obtained linking the specific surface area, pore volume, and pore diameter of the synthesized SiO₂ samples to the surface tension of the intrapore medium. It was shown that replacing the aqueous medium in the pore space with an organic liquid before drying significantly (~2 times) increases the adsorption monolayer capacity and affects the pore volume distribution. Based on the specific surface capacity of SiO₂ samples and Gibbs free energy (ΔG°) changes during sorption, it was concluded that the synthesis method does not significantly affect the physicochemical properties of their surfaces (the type and number of sorption sites per unit area) or the nitrogen sorption mechanism.