Fumed silica synthesis: influence of small molecules on the particle formation process

Abstract

Burning silicon tetrachloride in an oxygen-hydrogen flame produces fumed silica. This process is known for at least 50 years [1-5], but some important details are still uncertain. We would like to study several starting steps of fumed silica synthesis on the way from molecules to products. To do this we have performed quantum-level simulations of protoparticle and primary particle formation, from silicon dioxide molecules. Additionally, we have simulated the behavior of silica clusters in the presence of small molecules like water and hydrochloric acid. The reaction of silicon dioxide molecules leads to a silica cluster, which is covered with chemicaly highly active sites of one-coordinated oxygen atoms and three-coordinated silicon atoms. These clusters interact together and produce silica bulk like quartz glass. Reaction with water terminates the silica particle surface and leads to a complicated structure of the particle surfaces. The hydroxyl shell protects the particle body against the increase in particle size, but leads to aggregate and agglomerate formation.