Effect of preparation pH on properties of silica gel

Silica gels were obtained by drying the silica hydrogels formed at pH values between 1 and 4 at 100°C. The bulk density of the 2–3 mm diameter fraction decreased from 0·62 g cm-3 to 0·20 g cm-3 as the preparation pH increased from pH 3 to pH 3·65. The apparent density of silica gels was between 1·43 and 1·95 g cm-3. Isotherms for the adsorption of water vapour on samples prepared at different pH values showed hysteresis in all cases. Thermogravimetry analysis showed that the amount of bound water was in the range of 4·4 to 5·5% on a dry weight basis. Specific heats were determined by a differential scanning calorimetry method using a sapphire standard and were between 0·82 and 0·97 J g-1 K1. Copyright © 1990 Society of Chemical Industr