摘要：

Kinetic analyses of the formation reaction of colloidal silica spheres which are synthesized from ethyl silicate (EtSi), ammonia and a trace of water in ethanol are made by the transmitted-light-intensity and dynamic light-scattering methods. Sphere size versus time profiles from the two methods agree well especially at the beginning of the reaction. The polymerization starts after a certain induction time ( t i ) ranging from several tens of seconds to several minutes. t i increases as the concentrations of NH 3 , EtSi and/or H 2 O decrease. The apparent rates of the reaction, v ′ are estimated from the reciprocal periods between the intersections of the linear line with the initial and final horizontal lines in the cube root of the absorbance versus time plots. Log v ′ increases linearly with slopes of 1, 2 and 0.5 as the logarithms of the concentrations of EtSi, NH 3 and/or H 2 O increase, respectively. These results are consistent with the assumption proposed earlier that the polymerization mechanism of the formation of the small preliminary particles is followed by their coalescence to form large silica spheres.

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