Structure of Barite (001)− and (210)−Water Interfaces

Abstract

The structures of the barite (001) and (210) cleavage surfaces were measured in contact with deionized water at 25°C. High resolution (∼1 Å) specular X-ray reflectivity and atomic force microscopy were used to probe the step structures of the cleaved surfaces and the atomic structures of the barite-water interfaces including the structures of water near the barite-water interfaces. The barite (001) and (210) cleavage surfaces are characterized by large (>2500 Å) domains separated by unit-cell steps (7.15 and 3.44 Å steps for the (001) and (210) surfaces, respectively). This observation was unanticipated for the (001) surface in which adjacent BaSO 4 layers are displaced vertically by c/2 and symmetry related through a 2 1 screw axis along (001). The atomic structures of the two cleavage surfaces derived by X-ray reflectivity reveal that near-surface sulfate groups exhibit significant (∼0.4 Å) structural displacements, while Ba surface ion displacements are significantly smaller (∼0.07 Å). Water adsorbs to the barite surfaces in a manner consistent, in both number and height, with the saturation of broken Ba-O bonds; no evidence was found for additional structuring of the fluid water near the surface.

From Interfacial Water to Macroscopic Observables: A Review

“…A number of experimental and theoretical studies have been reported for the rutile (110)/water interface (Fitts et al 2005;Zhang et al 2004) and for the muscovite (001)/water interface Park and Sposito 2002;Wang et al 2005). Kerisit et al (2008) reported MD simulation results for the orthoclase (001)/water and orthoclase (010)/water interfaces that closely reproduce the experimental X-ray reflectivity data reported by Fenter et al (2003). The comparison between experimental data and simulation results was undertaken by generating an electron-density profile for adsorbed water molecules.…”

“…Stack and Rustad (2007) simulated water at the (001) barite/water interface. When compared to experimental X-ray reflectivity data obtained by Fenter and co-workers Fenter and Sturchio 2004), the simulated results showed profiles that were substantially different. Among the possible reasons proposed to explain this discrepancy is the fact that simulations are conducted on a very small surface area, necessarily perfect, while experiments are conducted on large samples which certainly contain some heterogeneity because, for example, of surface reconstruction and slight deviations in the cut angle used to prepare the surface (Stack and Rustad 2007).…”

“…X-Ray reflectivity data collection can then be accomplished at beam lines such as those available at advanced light sources. Fenter (2002) has provided a detailed description of the sample cell and experimental equipment necessary for conducting these experiments. Thus, a monochromator is used to select a specific incident X-ray wavelength and a Pt-coated mirror is often used for vertical focusing and harmonic rejection.…”

Prediction of the effects of size and morphology on the structure of water around hematite nanoparticles

“…Highly ordered water structure has been observed experimentally on a wide range of minerals including calcite (CaCO 3 ) (GEISSBUHLER et al, 2004), barite (BaSO 4 ) (FENTER et al, 2001), orthoclase (KAlSi 3 O 8 ) (FENTER et al, 2003), hematite (TANWAR et al, 2007;TRAINOR et al, 2004) and alumina ( -Al 2 O 3 ) (ZHANG et al, 2008). To gain added insight into this ordered structure, computer simulations provide a complementary tool for investigating this interface.…”

Precipitation in Pores: A Geochemical Frontier

“…These typically show modifi cations of the average positions of atoms in a few of the top-most monolayers of a crystal surface due to the creation of the interface. For example in the barite {001} surface, in XR experiments (Fenter et al 2001) and MD simulations (Stack and Rustad 2007), show a bulk-like structure after about three monolayers depth, which is about 1 nanometer (Fenter et al 2001) (Fig. 6).…”