Nucleation in confinement generates long-range repulsion between rough calcite surfaces

Abstract

Fluid-induced alteration of rocks and mineral-based materials often starts at confined mineral interfaces where nm-thick water films can persist even at high overburden pressures and at low vapor pressures. These films enable transport of reactants and affect forces acting between mineral surfaces. However, the feedback between the surface forces and reactivity of confined solids is not fully understood. We used the surface forces apparatus (SFA) to follow surface reactivity in confinement and measure nm-range forces between two rough calcite surfaces in NaCl, CaCl 2 , or MgCl 2 solutions with ionic strength of 0.01, 0.1 or 1 M. We observed long-range repulsion that could not be explained by changes in calcite surface roughness, surface damage, or by electrostatic or hydration repulsion, but was correlated with precipitation events which started at µm-thick separations. We observed a submicron-sized precipitate that formed in the confined solution. This liquid-like viscous precipitate did not undergo any spontaneous ripening into larger crystals, which suggested that confinement prevented its dehydration. Nucleation was significantly postponed in the presence of Mg 2+ . The long-range repulsion generated by nucleation between confined mineral surfaces can have a crucial influence on evolution of the microstructure and therefore the macroscopic strength of rocks and materials.

Crystallization in Confinement

“…The interaction between two polycrystalline calcite surfaces and their surface reactivity in confinement has also been studied using an SFA, [322,323] and similar systems have been considered using modeling approaches. [324,325] Experiments were conducted using calcite surfaces glued to two crossed cylinder disks, where the calcite thin films were deposited on mica using atomic layer deposition.…”

“…Solutions were saturated with CaCO 3 , and the influence of the additional electrolytes NaCl, CaCl 2 , and MgCl 2 was also explored. [ 322 ] Force curves were measured as a function of the surface separation, and repulsive forces were recorded in all cases. Despite the solution being saturated with respect to calcite, the calcite surfaces underwent minor dissolution, where this was attributed to the roughness of the films.…”

Ca2+ Ions Decrease Adhesion between Two (104) Calcite Surfaces as Probed by Atomic Force Microscopy

“…Reactivity, recrystallization, and the resulting surface roughening of calcite surfaces often correlate with a much higher magnitude and range of repulsion that would be expected from the theoretical EDL contribution. 33 …”

“…Since the measurement of forces between the two calcite surfaces is experimentally challenging, these forces have been directly measured and distance-resolved only in few works using atomic force microscopy (AFM) and a surface force apparatus (SFA). − Repulsive or slightly adhesive forces act between the two calcite surfaces in calcite-saturated water and have been attributed to hydration repulsion that counteracts the attractive van der Waals (vdW) forces. Higher ionic strength (IS) due to the addition of NaCl or the presence of sulfate ions has been found to increase the adhesion, likely as an effect of EDL screening and attractive ion correlation forces.…”

Real-time visualization of metastable charge regulation pathways in molecularly confined slit geometries

“…Also in nano-fluidics, stress-corrosion cracking, or geological dissolution processes, fluid-filled nano-channel geometries substantially alter ion diffusion (concentration gradient driven) and migration (field gradient driven) and the locally acting osmotic pressures, unlike in systems with limited spatial confinement [10][11][12][13] . Thus, experimental measurements of ion diffusion kinetics during a surface charging/discharging process in nano-cavities are essential to progress our understanding of charge regulation across all those systems.…”