Open AccessDissolution dynamics of the calcite-water interface observed in situ by glancing-incidence X-ray scattering
Author(s) -
Neil C. Sturchio,
R. P. Chiarello
Publication year - 1995
Language(s) - English
Resource type - Reports
DOI - 10.2172/510301
Subject(s) - calcite , dissolution , saturation (graph theory) , mineralogy , surface finish , analytical chemistry (journal) , chemistry , scattering , kinetic energy , surface roughness , x ray crystallography , cleavage (geology) , crystallography , crystal (programming language) , materials science , thermodynamics , diffraction , optics , metallurgy , physics , environmental chemistry , mathematics , combinatorics , quantum mechanics , fracture (geology) , computer science , composite material , programming language
Glancing-incidence X-ray scattering measurements made at the National Synchrotron Light Source were used to investigate dissolution dynamics in situ at the calcite-water interface. The relation between calcite saturation state and roughness of the calcite (1014) cleavage surface as a function of time was examined during pH titrations of an initially calcite-saturated solution. Systematic variations in roughness were observed as a function of saturation state as pH was titrated to values below that of calcite saturation. Different steady-state values of roughness were evident at fixed values of {Delta}G{sub r}, and these were correlated with the extent of undersaturation. A significant increase in roughness begins to occur with increasing undersaturation at a {Delta}G{sub r} value of approximately {minus}2.0 kcal/mol. The dissolution rate corresponding to this increase is about 1.5 x 10{sup 7} mmol/cm {center_dot} sec. This increase in roughness is attributed to a transition in the principal rate-determining dissolution mechanism, and is consistent with both powder-reaction studies of dissolution kinetics and single-crystal dissolution studies by atomic force microscopy. These data indicate some important potential applications of GIXS in the study of mineral-water interface geochemistry