Core/mantle-like interactions in an electric field

Reactions between metal and silicate phases, such as those that may occur at the core/mantle boundary, are charge transfer reactions—involving oxidation and reduction of chemical species. Therefore, the chemical potential driving force can be recast as an electric potential difference. Conversely, the application of an electric field across a metal/silicate interface is capable of driving chemical reactions. To explore the electrochemical behavior of a core/mantle-like boundary, the behavior of a liquid sulfide/silicate boundary in the presence of an externally applied electric potential difference was examined experimentally. The physical and chemical responses of this electrified interface include: (1) reaction zones containing new oxide phases at the ∼1 V level, (2) unusual partitioning of highly siderophile elements at ∼100 mV, (3) electrowetting at 10–100 mV, and (4) valence changes, indicating oxygen fugacity perturbations, at a level of ∼1–10 μV. An equivalent circuit diagram representing the experimental results is introduced, and extended to processes at the Earthʹs core/mantle boundary.