A Direct Current Polarization on the Interfaces of ZrO₂·CaO-molten Ag, Pb, Fe and Solid Pt-molten PbO-GeO₂, PbO-SiO₂, and Na₂O-SiO₂

Abstract

The mechanism of charge transfer process on metal-ionic conductor oxide interfaces was studied at elevated temperatures in various oxygen pressure range.
(1) Following cells were made with lime stabilized zirconia as solid electrolyte;
Ni. NiO or Mo. MoO₂/ZrO₂ CaO/molten silver, lead or iron.
When a current was supplied galvanostatically to this cell, the oxygen concentration overpotential was observed on the zirconia-molten metal interface. A linear relationship between exp (2F/RTη) and √t was obtained for every cell. This indicates that the diffusion of dissolved oxygen in molten metal is the rate controlling step of charge transfer process on the interface.
(2) A potential was applied potentiostatically between two of three platinum rods which were dipped into PbO-GeO₂, PbO-SiO₂ and Na₂O-SiO₂ melts. The supplied current across the examining platinum-molten oxide interface decreased with time. Plot of current i against 1/√t exhibited a linear relationship for every cell examined.
The slope of the line increased with po₂, with temperature, and decreased with the increase of SiO₂content in PbO-SiO₂ system.
These results were interpreted as follows; The applied overpotential is the oxygen concentration overpotential and the diffusion of di-atomic oxygen dissolved in molten oxide is the rate controlling step of the charge transfer process on the solid platinum-molten oxide interface.