Charging Phenomena at the Metal Oxide–Liquid Metal Interfaces and Determination of Excess Electron Density of Metal Oxide–Mercury Systems by the Induced emf Method

Abstract Interfacial charge in a metal oxide–liquid metal system is mainly due to the electron transfer between two phases. Many metal oxides accompany electronic defects, such as quasi-free electrons or holes in their lattices. When those oxides are brought into contact with a liquid metal, electrons in the oxide may transfer to the liquid metal phase, giving rise to an electrical double layer with a flat diffuse layer extended far into the bulk liquid metal phase. In this report, a new method based on the induced electromotive force (emf) is introduced to determine the excess electron density of the diffuse layer. The induced emf is simply generated by rotating a cell of liquid metal containing excess electrons in a solenoid and is only a function of the excess electron density and the rate of rotation velocity of the cell. For systems of NiO and Al 2 O 3 particles dispersed in Hg, oxides carried the positive charges on their surfaces by providing electrons for Hg. The excess electron densities in Hg were measured to be about 4.7×10 23 electrons/m 3 of Hg for NiO and 2.6×10 23 electrons/m 3 of Hg for Al 2 O 3 with a solid density of 1.1 wt% at room temperature.