Aggregation processes and formation of silico-calco-alkaline gels under high ionic strength.

This paper presents a systematic in situ study of the process of formation of silico-calco-alkaline gels starting from a liquid colloidal solution containing different alkaline ions and different calcium concentration until the final gel state. The combined use of X-ray and neutron small-angle scattering (SAS) and dynamical rheometry techniques lead to a consistent description of the structure of the aggregates and of the mechanisms of aggregation involved in gel formation. SAS results indicate that the aggregates are fractal objects, their structure strongly depending on calcium ion concentration. The differences in gelation kinetics for systems containing different alkaline ions were attributed to the effects of repulsive forces acting on the external surfaces of the fractal aggregates. The high ionic strength of the studied sols induces a non-classical dependence of these forces on the counter ion size.