Thèses

Mercredi 19 Septembre 2018 à 13h30.

Physico-chemical study of calcite colloidal suspensions: from macroscopic rheology to microscopic interaction

''Calcite (calcium carbonate) is an extremely widespread material that can be found naturally in rocks (i.e. marble, limestone) and is employed in many industrial fields such as paper filling, pharmaceutical, art or construction. Understanding the mechanical properties of calcite suspensions is a first step to improve the workability of the paste as well as the final properties of solid mineral materials.

We have carried out rheological measurements of calcite suspensions for a wide range of concentrations. The paste shows a typical gel behavior, with an elastic shear modulus and a yield strain. We have evidenced a minimum of this critical strain with concentration, a major prediction of the standard theory of colloidal gel, never verified so far.

We have then added simple salts to the suspension, to tune the interactions between calcite particles. The admixtured paste is then characterized by oscillatory and flow rheological experiments, zeta potential measurements, and chemical speciation and DLVO computations. Addition of calcium hydroxide improves initially the workability of the paste, eventually recovering a harder behavior. Addition of sodium hydroxide increases strongly the attraction between particles, inducing shear bands at the macroscopic scale. This correlation between shear banding and colloidal attraction is well known for emulsions but had never been verified so far for colloidal gels.

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