Da. Donatti et Dr. Vollet, STUDY OF THE HYDROLYSIS OF TEOS-TMOS MIXTURES UNDER ULTRASOUND STIMULATION, Journal of non-crystalline solids, 204(3), 1996, pp. 301-304
Pure and mixed tetramethoxysilane (TMOS) and tetraethoxysilane (TEOS)
were hydrolyzed at 35 degrees C, using oxalic acid as a catalyst and u
ltrasound stimulation. The hydrolysis reaction was carried out in a sp
ecially designed device, in which a heat flow steady state, between th
e ultrasound source and an external thermostatic bath, was maintained,
in the absence of reactions. The exothermic hydrolysis causes a time
dependent thermal peak. An induction time is apparent in pure TEOS bef
ore the hydrolysis peaks starts, which has been explained by the initi
al immiscibility gap of the TEOS-water system. The induction time was
found to be approximately of the same magnitude as in the HCl catalyze
d hydrolysis, in spite of the uncertainty accompanying the peak defini
tion. No induction period is apparent in pure TMOS, so that the hydrol
ysis starts with its maximum rate. Two independent thermal peaks in th
e mixed TMOS-TEOS samples were found, both associated to the respectiv
e hydrolyses of the pure component. The induction time for the TEOS hy
drolysis is decreased as more alcohol (and silanol) is produced in the
earlier TMOS hydrolysis. This effect is explained by improvement of h
omogenization by alcohol.