Effects of the water quantity on the solventless TEOS hydrolysis under ultrasound stimulation

The acid hydrolysis under ultrasound stimulation of solventless tetraethoxy silane(TEOS)-water mixtures was studied at 40 degrees C, by means of a heat flux calorimetric method, as a function of the initial water/TEOS molar ra tio (r) ranging from 2 to 10. The method is based on the time record of the exothermic heat peak of hydrolysis, arising after an induction time under ultrasound stimulation, which is a measure of the reaction rate. The hydrol ysed quantity was found to be approximately independent of the water/TEOS m olar ratio, even for r < 4. Polycondensation reaction takes place mainly fo r low water/TEOS molar ratio in order to supply water to allow almost compl ete hydrolysis. The overall process of dissolution and hydrolysis has reaso nably been described by a previous modelling. The dissolution process of wa ter in TEOS, under ultrasound stimulation and acid conditions, was found to be rather dependent of the alcohol produced in the hydrolysis reaction ins tead of the initial water quantity present in the mixture.