Effects of HCl on the ultrasound catalyzed TEOS hydrolysis as determined by a calorimetric study

The acid catalyzed and ultrasound stimulated hydrolysis of solventless tetraethoxysilane-water mixtures was studied at 39 degrees C as a function of HCl added to the mixtures (log[HCl](-1) ranged from 0.8 to 2.0). The reaction was carried out in a specially designed device, in which a steady state heat flow is maintained, while sonication is taking place, if no reaction is expected to occur. The exothermal hydrolysis reaction causes an increasing temperature (Delta T-t) as a function of the reaction time, t. The isothermal hydrolysis rate constant, k, has been evaluated from the experimental Delta T-t versus t data, after corrections for the increasing temperature effects, by using a method resulting from our theoretical modeling based on a dissolution and reaction mechanism. The hydrolysis rate constant fits closely a k proportional to [H+] law as expected for this kind of hydrogen-ion catalyzed reaction.