Aqueous chemistry and thermodynamic modelling of CaO–SiO2–H2O gels

Abstract

Some CaO–SiO₂–H₂O gels of controlled composition have been synthesised by the hydrolysis of mixed alkoxide precursors and by direct reaction between colloidal SiO₂ and Ca(OH)₂. The gels were equilibrated with water at 25 °C after different ageing treatments, and the water compositions analysed. A mathematical model describing the free energy of formation of the gel as a function of its composition has been developed which accounts for the experimental data. The model assumes that both SiO₂(amorphous) and Ca(OH)₂ can form limited solid solutions with an intermediate compound and hence only a small number of parameters is required to characterise the entire system.