Kinetics of Formation of Monodisperse Colloidal Silica Particles through the Hydrolysis and Condensation of Tetraethylorthosilicate

Abstract

Kinetic studies of the hydrolysis and condensation of tetraethylorthosilicate (TEOS) during the formation of uniform silica particles were performed through determining concentrations of TEOS and silicic acid by means of gas chromatography and a conductometer, respectively. It was shown that both hydrolysis of TEOS and condensation of Si(OH)4 are first order with TEOS and Si(OH)4, respectively, and the relationships of the hydrolysis and condensation rate constants with reaction condition variables, such as temperature, NH3 concentration, and H2O concentration, were determined. In addition, the particle growth rate was investigated with relation to the hydrolysis and condensation kinetics. Experiments showed that, during most of the reaction, the amount of formed particles is less than that of consumed TEOS, indicating that reaction intermediates exist during the process of silica formation. In the early stages of the Stöber process, the reaction intermediates include silicic acid and subparticles, while in the case of seed growth experiments without the formation of new particles or after the early stages of Stöber process, the reaction intermediates primarily consist of silicic acid and the growth rate of silica equals the rate of silicic acid condensation.