Formation of Molten Nanocraters on Electrodes during Charge Transfer with Conductive Droplets or Particles

当导电液滴或微粒接触电极时，电荷从电极转移到液滴或微粒上。虽然电荷转移的确切机制尚不清楚，但通常假设电荷转移不影响电极或与电极接触的液滴或颗粒。然而，最近的观察表明，电荷转移到水滴或其他粒子会在电极表面产生直径达一微米的陨石坑，这些陨石坑可以通过电子显微镜和原子力显微镜检测到。这个项目的目标是了解陨石坑形成的机制以及它如何影响电荷转移。一系列的实验将验证电荷转移过程中的焦耳加热使电极局部熔化的假设。由于周围流体的等离子体喷射，熔化的金属在压力下被推出。然后金属冷却并凝固，留下一个陨石坑。了解电荷转移的这些和其他细节可以提高各种工业电化学过程的效率，包括用于分离水和油的电脱乳化，以及用于控制颗粒排放的静电沉淀。该项目的成果将用于加州大学戴维斯分校的通识教育课程，该课程向初学者介绍科学和工程，每年有1500多名学生参加。带电物体在电极上的行为将通过一系列的原位实验来表征，包括高速视频、高分辨率计时法和高灵敏度光子计数。结果将与通过光学，电子和原子力显微镜获得的所产生的陨石坑的原位特征相结合。具体的实验将旨在直接测试所提出的陨石坑形成机制，包括系统地改变电极的熔点温度，周围流体的介电击穿强度以及固体导电颗粒的曲率半径。如果得到证实，这里提出的机制可以解释长期以来难以获得与预测电荷转移值的定量一致，因为陨石坑的形成物理地改变了电极。

CBET - 1707137PI: Ristenpart, William D.When a conductive droplet or particle contacts an electrode, charge is transferred from the electrode to the droplet or particle. Although the exact mechanism of charge transfer is not well understood, it is usually assumed that the charge transfer does not affect the electrode or the droplet or particle that contacts the electrode. However, recent observations show that charge transfer to water droplets or other particles creates craters in the electrode's surface up to a micron wide that can be detected by electron microscopy and atomic force microscopy. The goal of this project is to understand the mechanism of crater formation and how it affects charge transfer. A series of experiments will test the hypothesis that Joule heating during charge transfer melts the electrode locally. The molten metal is pushed out under pressure due to a plasma jet of the surrounding fluid. The metal then cools and solidifies leaving behind a crater. Understanding these and other details of charge transfer could lead to improved efficiencies in a variety of industrial electrochemical processes, including electrical de-emulsification, which is used to separate water from oil, and electrostatic precipitation, which is used to control particulate emissions. The results of this project will be used in a general education course at UC Davis that introduces beginning students to science and engineering and is taken each year by more than 1500 students. The behavior of charged objects at an electrode will be characterized by a series of in situ experiments, including high speed video, high resolution chronocoulometry, and high sensitivity photon counting. Results will be combined with post in situ characterizations of the resulting craters obtained by optical, electron, and atomic force microscopy. Specific experiments will be aimed at directly testing the proposed mechanism of crater formation, including systematically varying the melting point temperature of the electrode, the dielectric breakdown strength of the surrounding fluid, and the radius of curvature of solid conductive particles. If corroborated, the mechanism proposed here could explain the long-standing difficulty in obtaining quantitative agreement with predicted charge transfer values, since the crater formation physically alters the electrode.