A study of the hydrolysis pathway in oxalic acid catalyzed reacting TMOS-water mixtures under ultrasound stimulation

The hydrolysis of TMOS in oxalic acid catalyzed reacting TMOS-water mixture s, under ultrasound stimulation, was studied by fitting a simplified dissol ution and reaction modeling for samples, the hydrolysis rate of which had b een measured in a previous work. The reaction pathway represented in a tern ary diagram shows a heterogeneous step for the reaction which gradually pro gresses until complete homogenization of the system. Besides the water diss olved due to the homogenizing effect of the alcohol, ultrasound maintains a virtual and additional dissolution of water located at the interface betwe en the TMOS and water during the heterogeneous step of the reaction. The me an radius of the heterogeneity represented by water dispersed in TMOS was e valuated as around 150 Angstrom. The oxalic acid concentration accordingly increases the hydrolysis rate constant but its fundamental role on the solu bility of water in TMOS could not unequivocally be established.