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 fun ction 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 wh ich 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 o f the reaction time, t. The isothermal hydrolysis rate constant, k, ha s 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 rea ction mechanism. The hydrolysis rate constant fits closely a k proport ional to [H+] law as expected for this kind of hydrogen-ion catalyzed reaction.