Electric field effects on the growth of flame-synthesized nanosilica: a two-stage modeling

Abstract

Electric field effects on the kinetics of SiO2 formation, and the growth of silica nanoparticles formed in the flame (fumed silica) are studied theoretically and computationally, considering combustion of SiCl4 in the H2/O2 flame. An existing mechanism for the gas-phase part of this flame synthesis reaction is improved and used to derive instantaneous concentrations of the involved species. Quantum (DFT) computations are used to obtain thermodynamic data required for the calculation of equilibrium concentrations and reaction rate constants, assuming an overall (high temperature) equilibrium state. Kinetics equations based on a modified 43-step 24-species mechanism are established and solved to obtain concentrations at different temperatures and EF strengths. These concentrations are used as inputs for the Monte Carlo simulation of the growth of silica nanoparticles, considering also possibility of atomic displacements and vacancies. Effects of homogeneous electric field of different strengths on the growth of silica nanoparticles are investigated. Results of this study show that electric field changes the preferences of different paths of the mechanism of this flame synthesis reaction and changes composition of the flame via controlling orientation of the dipolar species, which consequently determine characteristics of the grown silica nanoparticles. Furthermore, EF effect is larger at lower temperatures.