Galvanostatic Polarization Measurements on a Soid Platinum-Alkali Silicate Melts

Abstract

Galvanostatic polarization measurements were made at 1350°C on a solid platinum-molten alkali silicate interface. From the analysis of the initial dccay up to 80μsec of the overpotential-time curves, the exchange current density has been determined as a function of the M₂O/SiO₂ molar ratio (M=Li, Na and K) and the oxygen partial pressure. (P_O2=1, 0.21 and 0.03atm) The exchange current density has been found to increase with increasing the M₂O/SiO₂ molar ratio and the oxygen partial pressure. Subsequent decay up to 1msec, 10msec, 100msec, 1sec and 5sec- of the overpotential curves has been studied on the assumption that mass-transfer controls the rate of the oxygen discharge reaction. At the constant M₂O/SiO₂ molar ratio, the slope in the overpotential-square root of time plots has been shown to be inversely proportional to the square root of an oxygen pressure. It was also found that the product of the solubility of and the square root of the diffusivity of soluble oxygen and oxygen ion increases with the increase of the M₂O/SiO₂ molar ratio. The product also increases with changing M₂O from Li₂O to Na₂O to K₂O in this order at a constant M₂O/SiO₂ molar ratio.