HR: 0800h
AN: B21B-0868    [Abstracts]
TI: Step Velocity Distributions, Step Spacing, and Stepwave Theory: Experimental Evidence and Modeling Results
AU: * Arvidson, R S
EM: rsa4046@ruf.rice.edu
AF: Rice University, Department of Earth Science MS-126 P.O. Box 1892, Houston, TX 77251-1892 United States
AU: Zhang, L
EM: lizhang@rice.edu
AF: Rice University, Department of Earth Science MS-126 P.O. Box 1892, Houston, TX 77251-1892 United States
AU: Vinson, M D
EM: mvinson@rice.edu
AF: Rice University, Department of Earth Science MS-126 P.O. Box 1892, Houston, TX 77251-1892 United States
AU: Luttge, A
EM: aluttge@rice.edu
AF: Rice University, Department of Earth Science MS-126 P.O. Box 1892, Houston, TX 77251-1892 United States
AB: Much of current attention in mineral dissolution reaction kinetics is devoted to the study of the relationship between the overall "bulk" rate, reflected in time-averaged solute fluxes observed in a well-mixed reactor, versus the rates of individual, "elementary" processes, such as kink nucleation, attachment and detachment, surface and edge diffusion, and resultant step motion. Regardless of the details of the interaction between these processes, implicit in many interpretations is the notion that the relationship between them is a deterministic one, i.e., that if a given set of physical and chemical conditions is imposed on a crystal surface, a predictable rate will result. This assumption has currency in many recent AFM studies of carbonate mineral dissolution that observe that parameters such as step velocity and interstep spacing acquire characteristic values. This assumption is also the basis for kink transport models. Despite an incomplete understanding of the complex relationships between kink density and kink detachment rate, characteristic values for these individual rates guarantee a predictable cumulative "bulk" rate. However, not all AFM observations validate this assumption. For example, etch pits forming on calcite show a large variation in the velocity of steps under otherwise constant conditions that may reflect mechanistic differences. These include steps migrating within relatively flat etch pit interiors, bunched steps that comprise bounding vicinal faces, and curved or roughened steps often formed during etch pit coalescence. Here we examine experimental evidence collected using both AFM and vertical scanning interferometry for these relationships in light of a theoretical framework that relates step velocity, surface diffusion, free energy, and other relevant parameters. Our goal is to understand how variations in surface micro-topography may contribute to intrinsic rate variability, and to use this understanding to clarify the relationship of "bulk" rates to surface area.
DE: 3620 Crystal chemistry
DE: 1886 Weathering (1625)
DE: 1045 Low-temperature geochemistry
DE: 0400 Biogeosciences
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting