Viscosity Change of the Silica Sol during Hydrolysis of Ethylsilicate

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  • エチルシリケートの加水分解過程におけるケイ酸ゾルの粘度の変化

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The viscosity change of silica sol in the process of hydrolysis of ethylsilicate is measured by the falling ball method. With ethylsilicate 40, a pentamer on average of ethyl-silicate, as a starting material, the hydrolysis proceeds as Si5(OC2H5)12O4+12H2O→Si5(OH)12O4+12C2H5OH. With enough quantity of H2O for hydrolysis, the sol transforms to a gel quickly. In this study, the mole ratio H2O/ethylsilicate 40 is 1.83~2.83; the amount of water is smaller than that of the stoichiometric ratio. At temperatures below 25°C, viscosity increases to several poises in about 30 days, then due to the lack of water, the viscosity increases slowly as log η∝t for about 60 days up to about 100 poise. Finally the viscosity increase is remarkably accelerated.

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