Interfacial Impedance between Solid Platinum and Liquid Oxide Solutions

Abstract

Dispersion of AC-impedance at the interface of solid platinum/oxide or halide melts has been determined at 800 to 1 300°C under pure oxygen, air or argon atmosphere. The liquid solutions studied are; a) 60, 50, and 40 mol % PbO-GeO₂, b) 60, and 40 mol % PbO-SiO₂, c) pure CaCl₂, d) 50 mol % CaF₂-MgF₂, and e) 47mol% CaF₂-MgF₂. The interface impedance, measured by both parallel and series connections of a variable capacitance and a variable resistance in the bridge, has been found to increase with decreases of the frequency, temperature, and oxygen pressure in the atmosphere, and with the increase of silica or germanate content.
Under the assumption that the double layer capacity is independent of the frequency, a calculation for the ohmic and capacitive components of the measured interface impedance has been made. By so doing, these two-components have been plotted against reciprocal square root of the frequency. Except for the frequencies higher than 5 kilocycles, a good linear relation has been obtained in the diagrams. Thus, it seems that the interface impedance is predominantly composed of a diffusion impedance. The most likely species for the diffusion is deduced to be di-atomic oxygen dissolved in liquid oxide solutions, because the impedance has depended on both oxide composition and oxygen pressure in the gas phase.
The probable double layer capacity is in the range of 700 to 1 100 μF square centimeter but its relation to temperature and the oxide composition has not been clarified due to large experimental errors.