Simple ions control the elasticity of calcite gels via interparticle forces

Abstract

Suspensions of calcite in water are employed in many industrial fields such as paper filling, pharmaceutics, heritage conservation or building construction, where the rheological properties of the paste need to be controlled. We measure the impact of simple ions such as calcium, sodium or hydroxide on the elasticity of a nanocalcite paste, which behaves as a colloidal gel. We confront our macroscopic measurements to DLVO interaction potentials, based on chemical speciations and measurements of the zeta potential. By changing the ion type and concentration, we go beyond the small repulsion regime and span two orders of magnitude in shear modulus. Upon addition of calcium hydroxide, we observe a minimum in shear modulus, correlated to a maximum in the DLVO energy barrier, due to two competing effects: Calcium adsorption onto calcite surface rises the zeta potential and consequently the electrostatic repulsion, while increasing salt concentration induces stronger electrostatic screening. We also demonstrate that the addition of sodium hydroxide completely screens the surface charge and leads to a more rigid paste. A second important result is that carbonation of the calcite suspensions by the atmospheric CO 2 leads to a convergent high elasticity of the colloidal gels, whatever their initial value, also well rationalized by DLVO theory and resulting from a decrease in zeta potential and in surface charge density.

Turning a yield-stress calcite suspension into a shear-thickening one by tuning inter-particle friction

“…The yield stress is due to adhesion of strength σ a ∼ 0.6 Pa stabilising inter-particle frictional contacts. The presence of adhesion suggests there is van der Waals attraction (Liberto et al 2019) and that the magnitude of electrostatic repulsion, controlled by the concentration of dissolved lattice ions (Al Mahrouqi et al 2017), is insufficient to stabilise the particles. To Fig.…”

Interparticle attraction controls flow heterogeneity in calcite gels

“…The change of solution physico-chemistry, due to the introduction of sodium and calcium hydroxide at these concentrations, leads to an increase of attraction between the calcite particles, which has been characterized in ref. 8 for the physico-chemical conditions used in this study. The authors found that incorporating 97 mM sodium hydroxide and 3 mM calcium hydroxide in a pure calcite paste leads to a decrease of both the zeta potential, from z = 9.3 AE 1 mV to z = À2.4 AE 1, and the Debye length, from l D = 11 nm to l D = 1 nm.…”

“…The Taylor-Couette cell is filled by the calcite dispersion to a height of 60 mm and closed by a homemade lid which reduces the contact with atmosphere, so that experiments can be conducted on the same sample for at least 4 h without any significant impact of evaporation or carbon dioxide exchange with the atmosphere. 8 The rheological protocol starts with a long preshear step of 90 min under an imposed shear rate of _ g = 100 s À1 . This allows us to drastically reduce the subsequent evolution of the sample mechanical properties over time and/or strain accumulation.…”

“…Adding calcite to water leads to the formation of colloidal gels which are often used to mimic early age cementitious materials, [3][4][5][6] whose mechanical properties depend on the calcite solid fraction, the interparticle forces and the addition of superplasticizers 4,5,7 or of specific ions. 3,8 For pure calcite gels, large solid fraction and/or attraction between calcite particles result in the formation of a gel whose mechanical response depends on the applied stress. Below a critical stress referred to as the yield stress, the system responds like an elastic solid while above this critical stress, it flows like a liquid.…”

“…9 This observed intermediate behavior between a liquid and a solid is interesting for applications but makes the understanding of calcite gels more complex. Recent works have explored the links between elasticity and microstructure 10 and between elasticity and interparticle forces 8 in calcite gels over a wide range of volume fractions. In particular, the dependence of the elastic modulus on the calcite concentration is well described by the classical fractal model for colloidal gels proposed by Shih.…”