The Hydrothermal Reaction between Calcium Hydroxide and Silica Gel (CaO/SiO₂=1/1 Molar Ratio) at Lower Temperature Range

Abstract

The hydrothermal reaction between calcium hydroxide and silica gel at the temperature range from room temperature to 80°C was investigated.
1) The admixed tablet of CaO/SiO₂=1/1 in molar ratio was heated in a small autoclave at the temperature range of 50-80°C. The initial reaction proceeded rapidly, and was followed by the slowdown of the reaction rate. The activation energy of the initial reaction was calculated to be 17 kcal/mol by use of the Jander's equation.
2) When silica gel was added to the saturated lime solution, its pH value decreased rapidly within several minutes, and then decreased slowly with the reaction time.
3) Contents of silanol groups in the silica gel estimated by adsorption quantity of methyl red in benzen solution and the reactivity of silica gel were decreased with the increase of treatment temperature.
4) The reaction between calcium hydroxide and silica gel in a grinding ball mill proceeded more rapidly than in a closed still vessel.
X-ray diffraction pattern and electron microphotograph revealed that the reaction products of above two grinding methods were different each other.