Physicochemical Aspects of the Hydrolysis

The acid hydrolysis of TEOS may be formulated as SiOR + H2O where R represents the ethyl group and ko is a second-order rate constant. 

When the container is installed in air at room temperature, the ultrasound makes the temperature attain a value as high as 80°C and then stabilize at a lower temperature ( 70°C). The measured temperature should be attributed to the boiling point of the ethanol release, accounting for the exothermic hydrolysis reaction. 

The reaction beaker could be surrounded by a thermostatic bath to ensure local temperature control [42, 46, 47], water HCl mixtures of constant volume (35 ml) with a molar ratio of 1 5 0.0089 and a pH -1.5 and a bath temperature held at 26.5°C present their exothermic peak after 3-4 min of sonication (20 kHz). This time depends on the dissipated ultrasound power, the maximum occurring for K - 0.9 W cm . The coupling between the ultrasound and the heterogeneous mixtures does not seem too good for higher ultrasound power [46]. The oxalic acid catalyzed TEOS hydrolysis peak shows a less pronounced form when compared to the HCl catalyzed one [47]. 

The parallel autocatalytic path that helps homogenize the initial system and favors the subsequent condensation reaction is 

Tr is the thermostatic bath temperature. Reprinted with permission from [40]. 

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