0000000000059954
AUTHOR
Fabien Gaboriaud
Aggregation and Gel Formation in Basic Silico−Calco−Alkaline Solutions Studied: A SAXS, SANS, and ELS Study
Gelation of strongly basic silico−alkaline solutions was promoted by appropriate additions of calcium ions. The structure of the aggregates formed in the precursor sols and the resulting gels were studied, within a wide length scale, using small-angle X-ray, small-angle neutron, and elastic light scattering. The study of the kinetics of aggregation was performed in situ. The experimental results demonstrate that gels are composed of aggregates exhibiting a fractal structure, large particles formed in the solutions just after calcium addition and, in some cases, small primary particles remaining in the solution phase. The structural features of the gels are strongly dependent on the concentr…
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 attr…
Structural model of gelation processes of a sodium silicate sol destabilized by calcium ions: combination of SAXS and rheological measurements
This study deals with the physico-chemical processes involved in the formation of basic fractal silica gels derived from a sodium silicate sol destabilized by calcium ions. Using small-angle X-ray scattering and dynamic rheological measurements, structural and viscoelastic properties have been investigated in situ during aggregation and gelation processes. The experimental results lead to a consistent model that describes the structural features and aggregation mechanisms involved in the formation of these gels.
The structural properties of soda–silicate sols and of the lime–soda–silicate gel formation
Abstract Alkaline silicate solutions were prepared with varying SiO 2 –Na 2 O ratios, Rm=[SiO 2 ]/[Na 2 O]=2 or 3, with a constant silica concentration equal to 1.5 M. The structure and the number fraction of different silicate molecular species present in the solutions were classically determined for molar ratio Rm=2 using 29 Si nuclear magnetic resonance ( 29 Si NMR). In the case of the sample with Rm=3, for which no NMR data was available, we used small-angle X-ray scattering (SAXS) experiments to get this information. The SAXS model was previously tested with Rm=2 silicate solution. When Ca ++ is added to alkaline silicate solutions, a gel is obtained under well-defined conditions. The …
29Si NMR and Small-Angle X-ray Scattering Studies of the Effect of Alkaline Ions (Li+, Na+, and K+) in Silico-Alkaline Sols
Alkali−silica reactions (ASR) which occur in concrete can be simulated in laboratory by destabilization of silico-alkaline aqueous solutions by addition of calcium ions. The relevant features of the reaction depend on the nature of alkaline ions (Li+, Na+, or K+) and on the silica/alkaline ratios which fix the distribution of the molecular species in the precursor solution. 29Si NMR spectroscopy and small-angle X-ray scattering (SAXS) techniques were used to study the structure and size distribution of molecular and colloidal species in sols with different silica/alkaline molar ratio and several types of alkaline ions. Experimental SAXS curves were simulated using a simple structural model …