Chemistry, Physics and Technology of Surface

ISSN 2518-1238 (Online), ISSN 2079-1704 (Print)

Aerogels are gels in which the liquid phase is completely replaced by a gaseous one. They form a new class of solids with a very low density, a large specific surface area and high porosity, which opens up wide possibilities for their practical application. ZrO₂-SiO₂ aerogels, due to the strong binding energy of Zr-O-Si, very low thermal conductivity, and the presence of acid and basic centers, exhibit excellent properties like aerospace heat insulators, selective sorbents, catalysts, and catalyst supports for high-temperature reactions. The traditional way of obtaining aerogels is formation of a branched, three-dimensional, irregular network of wet gels by sol-gel synthesis from alkoxides of elements, aging of gels, replacement of intermicillar water by organic liquids with low surface tension and careful removal of the solvent by drying under supercritical conditions or under ambient pressure. But alkoxides of the elements are expensive and toxic, drying at elevated pressures requires special equipment and is also expensive and energy-intensive, and drying at atmospheric pressure requires complicated and lengthy gel modifications. In this work, the task was posed, on the basis of the direct method of large-scale sol-gel synthesis of highly porous, nanostructured, spherically granulated zirconium silicates from aqueous solutions of cheap, accessible salts, to obtain materials of aerogel type, without resorting to lengthy equipmently and chemically complex methods of processing the resulting hydrogels. The gels were prepared by forming a zirconium carbonate complex from aqueous solutions of ZrOCl₂ and K₂CO₃ and its subsequent interaction with a Na₂SiO₃ solution by their coagulation in a drop. The obtained strong spherical granules of ZrO₂ SiO₂·nH₂O hydrogel were thoroughly washed from impurities with distilled water and subjected to hydrothermal treatment for various times, followed by decantation with ethanol mixed with benzine or alkothermal treatment in this mixture in tightly closed containers at supercritical temperature for ethanol. The heat resistance of the samples was determined by calcining them in air at high temperature. Using SEM, XRD, and N₂ adsorption / desorption methods, it has been found that the amorphous Zr-Si materials obtained containing 45 wt. % ZrO₂ have a specific surface area of more than 500 m²/g, pore volume > 2 cm³/g, average pore diameter of ~ 18 nm, wide mesopores with a diameter of ~ 28 nm, bulk density less than 0.3 g/cm³, which typical for aerogels based on oxides of metal and silicon, and exhibit high thermal stability.

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