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 Earth's core/mantle boundary.