Sol–Gel Kinetics Followed by Cylindrical Attenuated Total Reflectance Infrared Spectroscopy

This paper describes a unique solution infrared technique, a cylindrical attenuated total reflectance cell, to monitor in situ kinetics of the sol‐gel process, especially at short times after mixing. The sol‐gel kinetics of acidic ethanol : TEOS : Al(III) solutions have been followed as a function of temperature and aluminum concentration. The hydrolysis rate and the condensation rate increase with temperature and Al/Si ratio. The Al(III) hydrolysis and concomitant increase in acidity increase the reaction rate. By controlling the initial pH, it is seen that a higher Al(III) concentration itself increases the reaction rate. The properties of a sol‐gel glass depend upon the kinetics, which are controlled by the processing conditions, including cation content.