Water-Induced Reconstruction that Affects Mobile Ions on the Surface of Calcite

Abstract

Time-sequenced contact-force micrographs show that the (104) calcite cleavage surface reconstructs in humid air through pit formation and film growth. After 8 h at 80% relative humidity (RH), 50% to 80% of the surface is covered by islands that are flat-topped and 1-nm high. The lateral growth rates of individual islands are 4.2+/-0.4 nm min-1 in the 41 direction and 1.8+/-0.4 nm min-1 in the 48 direction, resulting in islands having distinct major and minor axes. On some samples, a contiguous, 1.5-nm-high film rapidly grows between the islands and the pits. The areal expansion rate of the film is 500 times faster than that of the islands. Gaps between the contiguous film and the islands expand and contract, which suggests that mass is exchanged between them and that both are loosely bound. Complementing the topographic images, polarization heights are simultaneously measured by polarization-force microscopy. The polarization heights of the islands and the contiguous film are -6 to -10 nm and -4 to -5 nm, respectively, compared to their respective topographic heights of +1.0 and +1.5 nm. Under our experimental conditions, the polarization heights are a surrogate for the local dielectric constant of the sample epsilon and arise from a convolution of the mobility and the density of surface ions. The polarization heights imply that epsilonsubstrate>epsilonfilm>epsilonisland. Changes in topographic and polarization heights at 20% and 50% RH suggest that the structures of the islands are in dynamic equilibrium with the adsorbed water. Our evidence suggests that the islands contain loosely bound water and may therefore be a hydrated calcium carbonate phase stabilized by the calcite surface.

Growth modification of seeded calcite using carboxylic acids: Atomistic simulations

“…Even stable surfaces such as the ð1 0 1 4Þ surface have been shown to reconstruct in moist air via pit formation and film growth [57], making it reasonable to consider defective stepped surfaces in our simulations. In order to have an estimate of the number of carbonate groups to be removed, experimental zeta-potential measurements (À13 mV) at low CO 2 partial pressure [58] were considered and the surface charge density u calculated via the surface potential w as given by [59].…”

Pore-scale investigation of residual oil displacement in surfactant–polymer flooding using nuclear magnetic resonance experiments

“…Oil was removed, as the emulsion was displaced through the formation, rather than tending to adhere to pore surfaces, resulting in an incremental oil recovery. In summary, the incremental oil recovery was attributed to the synergism between polymer and surfactant (Kendall and Martin 2007;Lai et al 2014). …”

A high-pressure atomic force microscope for imaging in supercritical carbon dioxide

“…It is worth noting that the range of the piezoelectric scanner is temperature-dependent and must be calibrated at the target operating temperature. From Hooker, 30 one can estimate the temperature dependence of the transverse strain constant (d 31 ) for PZT-5A at 8 × 10 −12 m V −1 C −1 between the temperature range of 0 • C -50 • C. Given that the transverse strain constant is -173 × 10 −12 m V −1 at 298 K, a 13 • temperature increase (from our 295 K room temperature) would increase d 31 by approximately 6%. This change is consistent with our recalibration settings (e.g., 77.1 nm V −1 versus 72.0 nm V −1 for y sensitivity).…”

“…This dynamic process that is occurring on the surface is likely due to changes in surface chemistry that have occurred during the induction period between cleavage and imaging. Kendall and Martin 31 have shown using polarization force microscopy that a 1.5 nm high film forms on the surface of calcite under humid conditions which they attribute to the formation of a hydrated calcium carbonate phase that is stabilized by the underlying calcite surface. It is not unreasonable to expect that flowing anhydrous scCO 2 over the surface of such a film would dehydrate the loosely bound water in this phase and result in the decomposition of this overlayer phase.…”