Abstract

Liquid-state 29Si NMR was used to investigate the hydrolysis and condensation kinetics of ammonia-catalyzed tetraethoxysilane (TEOS) in methanol system. The reactive rate constants were calculated by applying first-order reaction approximation and the steady state approximation theory. The reaction orders with respect to TEOS, ammonia and water were derived, as well as the activation energies and the Arrhenius constants. It was found that the formation of intermediate species Si(OH)(OEt)3 was the rate-limiting step and its reaction rate equation was rTEOS=7.41×10−3[TEOS][NH3]0.333[H2O]0.227. Higher reactive temperature benefited the hydrolysis of TEOS. The results presented here indicated quantificationally that the formation of colloidal SiO2 particles was controlled by the initial hydrolysis of TEOS.

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