Одержання цирконійсилікатних матеріалів типу аерогелів з водних розчинів солей Na2SiO3 та ZrOCl2

• Date: 2020
• Main Authors: Kravchenko, M. V., Redkina, A. V., Konovalova, N. D.
• Format: Article
• Language: English
• Published: Chuiko Institute of Surface Chemistry National Academy of Sciences of Ukraine 2020
• Subjects: ZrO2-SiO2 аерогелі; золь-гель синтез; суперкритична сушка; алкотермальна обробка; мезопоруваті матеріали
• Online Access: https://www.cpts.com.ua/index.php/cpts/article/view/559
• Journal Title: Chemistry, Physics and Technology of Surface

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.