Hydrothermal SiO2 Nanopowders: Obtaining Them and Their Characteristics

Silicic Acid Polymerization and SiO2 Nanoparticle Growth in Hydrothermal Solution

The approach of numerical simulation of orthosilicic acid OSA polymerization and SiO₂ nanoparticle formation in hydrothermal solution have been developed based on the model of the homogeneous stage of nucleation and the subsequent growth of particles. The influence of surface tension on the interface of SiO₂–water, the rate of molecular deposition, and Zeldovich factor Z were evaluated. Temperature dependence on time, pH, initial OSA concentration, and ionic strength are the main parameters that determine the kinetics of colloid phase formation, the final average size of SiO₂ nanoparticles, and the particle size distribution and its polydispersity index. The results of the numerical simulation were verified with experimental data on OSA polymerization and measurement of nanoparticles sizes using the method of dynamic light scattering in a wide range of temperatures of 20–180 °C, pH = 3–9, SiO₂ content C_t of 300–1400 mg/kg, and ionic strength I_s of 0.0001–0.42 mol/kg. The results obtained can be used in the technology of hydrothermal synthesis of sols, gels, and nanopowders to regulate the kinetics of OSA polymerization and SiO₂ nanoparticle growth, particle size distribution, morphology, and structure of products.