Continuous Ammonium Silicofluoride Ammonification for SiO2 Nanoparticles Preparation in a Microchemical System

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The ammonium silicofluoride ammonification process is a potential atomic economical process for nanosized silica preparation. In this work, this process was continuously conducted in a micropores dispersion microreactor and specially investigated. The exploration on the evolution of the yield and the specific surface area of product with reaction proceeding under various feeding conditions indicated that both of two consequent stages of fast precipitation and precipitate aging may occur remarkably in the microchemical system. However, their overlap could be reduced by enhancing mixing and strictly controlling the residence time. Correspondingly, this process could stably preparing high-quality SiO 2 nanoparticles (specific surface area >400 m 2 /g) at equilibrium yield. Furthermore, optimization on reaction temperature was discussed, and the adaptability of high concentration (NH 4 ) 2 SiF 6 as feed was tested as well. This research provided fundamentals and a guide for developing and designing an industrial production technology of nanosized silica based on the ammonium silicofluoride ammonification process.