HR: 1340h
AN: B33C-1039    [Abstracts]
TI: Reconstruction of Calcite in Response to Surface Hydration
AU: * Kendall, T A
EM: tkendall@deas.harvard.edu
AF: Harvard University, Division of Engineering and Applied Sciences, 29 Oxford St., Pierce Hall, Room 122, Cambridge, MA 02138 United States
AU: Martin, S T
EM: smartin@deas.harvard.edu
AF: Harvard University, Division of Engineering and Applied Sciences, 29 Oxford St., Pierce Hall, Room 122, Cambridge, MA 02138 United States
AB: Molecular level observations of a calcite surface equilibrating in response to water sorption will be presented. Changes in surface topography are directly linked to time dependent trends in surface ion density and mobility. This information is essential to a comprehensive mechanistic model of calcite dissolution and growth and, thus, is key to a kinetic description of biomineralization. Time sequenced AFM micrographs show that the (104) calcite cleavage surface reconstructs over several hours under two to three monolayers of water. Reconstruction consists of 1 nm high, flat-topped islands growing between expanding surface pits. The orientation of the islands in a single direction indicates a crystallographic influence from the substrate. The irregular shape of the islands and mass balance considerations suggest a hydrated calcium carbonate island phase. Importantly, the hour scale evolution of the surface is correlated with the mobile ion response collected using polarization force microscopy. One observable is maximum polarization force (Fmax) which trends with surface ion density. Completion of surface reconstruction coincides with a drop in Fmax to a minimum. The loss of surface charge presumably results from mobilization, extended dehydration and precipitation of surface ions. As such, this work provides a quantitative connection between mobile surface ion diffusion and surface reconstruction.
DE: 0412 Biogeochemical kinetics and reaction modeling (0414, 0793, 1615, 4805, 4912)
DE: 0419 Biomineralization
DE: 1039 Alteration and weathering processes (3617)
SC: Biogeosciences [B]
MN: Fall Meeting 2005