Nucleation and growth processes are fundamental to crystallization reactions in general and geochemical mineralization in natural and engineered systems in particular.  Barite (barium sulfate) formation represents a model process from which the nucleation and growth kinetics can be studied using experimental microscopy techniques.  In this work, nucleation of barite on glass substrates has been investigated using atomic force and optical microscopy.  The surface density of heterogeneously nucleated barite crystallites was found to depend on the solution supersaturation, as was expected, however, experimental evidence indicates that the local nucleation process is affected by the presence of the AFM probe and cantilever.  In barite growth studies, barite (001) surfaces were subjected to supersaturated solutions containing various alkali metal chloride salts as background electrolyte.  In LiCl solution, spiral growth hillocks on the barite surface were comprised of polar [010] steps and non-polar〈120〉steps at ionic strengths of 0.05 and 0.1 M. [010] steps were not observed at lower ionic strength. In NaCl solutions, hillocks displayed greater prominence of the [010] steps when compared with LiCl. From the saturation state dependent studies, it was found that the kinetic coefficient for step growth increased by 200% when ionic strength increased from 0.01 M LiCl to 0.1 M LiCl. When KCl was used as the background electrolyte, conversion from a surface dominated by 〈120〉 steps to a surface consisting primarily of [010] steps was observed, however, a thorough explanation for this phenomenon was hampered by changes in the surface – tip interaction which led to poorly resolved surface features. When RbCl was used as the background electrolyte, the growth of hillocks was completely inhibited whereas growth from CsCl solutions yielded growth hillocks consisting exclusively of 〈120〉 steps.  Interpretation of the experimental results suggests the main role of the cation is to affect the kinetics of 〈120〉 step growth, which in turn, influences the hillock morphology.

Scanning probe microscopic studies of mineral nucleation and growth

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.