Abstract
AbstractA high surface area silica gel was structurally modified by autoclaving in ammonium hydroxide solutions with pH values of 9–12, at temperatures of 100–180°C, and for periods up to 5 h. Drastic variations in the texture of the xerogel took place leading to a considerable decrease in the specific surface, and to an accompanying increase in the mean particle diameter, pore radius, and number of OH groups per unit area. The extent of change depends generally on the temperature, duration of treatment, and pH of solution, although the last factor seems to be the most prominent. Such variation is ascribed to the enhanced dissolution of silica in the alkaline solution. Activation energies of hydrolysis of the siloxane bond were calculated as 17.2–19.0 kJ/mol, from a relationship correlating change in surface area with time.
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