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Project Progress

We have successfully begun a research program examining how electrochemical processes (e.g. electroplating, corrosion, biological metabolism) act on stable isotopes of transition metals, starting with Fe. A first series of experiments showed that electroplated Fe becomes increasingly fractionated as the electrochemical driving force increases in an aqueous electroplating experiment. These results, together with a new theory based on classical statisticall mechanics of charge transfer processes, were published this year in Geochimica et Cosmochimica Acta.

The theory we developed provides a general explanation for both thermodynamic and kinetic behavior of stable isotopes in electron charge transfer systems. The theory makes a series of predictions about how electrochemical stable isotope fractionation is influenced by a variety of factors, including solution chemical speciation, solution concentration, equilibrium fractionation factors, and temperatures. Currently, we are systematically testing the predictions for Fe electroplating, and will continue to examine electrochemical processes in other stable isotope systems, such as Cr.

Our newest laboratory experiments suggest that as the concentration of the FeCl₂ plating solution is reduced, the slope of the fractionation vs. voltage plot becomes less strong, and ultimately changes sign, a result in concordance with our theory and predictions of equilibrium fractionation [Schauble et al., 2001] (see Fig. 1). However, the results also suggest that mass transport may be playing a role in the observed fractionation, as well as the electrochemical effect.

This research program is helping to provide a tie between the electrochemical-based metabolism of (all?) biotic systems, and potential stable isotope geochemical observables.

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