V.V. Potapov, K.G. Sobolev, D.S. Gorev
Russian Acadamey of Sciences; University of Wisconsin-Milwaukee,
Keywords: hydrothermal solution, SiO2 nanoparticles, membranes, the structure of calcium silicate gel, concrete, agriculture, medicine
Summary:Technology of production of new type of amorphous nano-SiO2 in the forms of sols, gels, and powders with precursor based on hydrothermal solution was developed. Amorphous nanodispersed silicon dioxide SiO2 is currently one of the most common nanomaterials. The relatively low cost of production and its physical and chemical properties make it possible to obtain and use nanosilica in large quantities. In various forms of nanopowders, gels, xerogels, aerogels, sols and sol-gel synthesis products, nanosilica is used as an independent product or one of the components of the final product. A new renewable source for the production of nanosilica is a hydrothermal solution exists in the depths of deposits as a result of the interaction of water with rock minerals at elevated temperatures and pressures. The processes of orthosilicic acid polycondensation (OSA), ultrafiltration membrane concentration, sol-gel transition, and cryochemical vacuum sublimation were studied. The technological scheme can to regulate average nanoparticles diameter, specific surface area, density, diameters, and pore’s volume of nanopowders, density of surface silanol groups, sizes of fractal agglomerates. SiO2 nanoparticles in combination with microfiber were used for enhancement of Portland cement concrete’s characteristics: compressive and flexural strength, impact viscosity of destruction, abrasive resistance, water impenetrability, frost resistance, for protective hydrophobic coatings and for cement composites development. It was achieved by acceleration kinetics of Portland cement hydration, decreasing of pore diameters and volume and by modification the nanogranules structure of hydrates of calcium silicate CSH gel. When modifying concrete with a combination of hydrothermal nanoparticles SiO2 – basalt microfiber, a synergistic effect is manifested: the flexural strength increases by 3.4 times, the specific energy of impact destruction - by 22.2 times, the impact viscosity coefficient - by 2.7 times. Nanomodification with hydrothermal SiO2 nanoparticles is used in heavy weight concrete, and also has broad prospects for use in concrete with cement-substituting materials – silica, fly ash, slag, aluminosilicate additives, in monolithic and block construction, construction of transport bridges, 3D-printing. Untoxic hydrothermal SiO2 nanoparticles with specific surface area up to 500 m2/g and high biochemical activity in cells of plants stimulated the growth and development of agricultural plants improved crop yields. Hydrothermal SiO2 nanoparticles have potential applications in medicine as entherosorbents, for drug delivery and for bone structure and strength improvement.