Surface Active Effect of Na2O on the Rate of CO2 Dissociation on the Surface of Molten FeOx-Na2O and FeOx-SiO2-Na2O Systems

Abstract

It is well known that P2O5 and Na2O have strong surface active effect in the molten oxide systems and affect the rate of oxidation or reduction of melts. In the previous work, the effect of P2O5 addition on the rate of CO2 dissociation on the surface of FeOx (FeO and Fe2O3)-based molten oxides was investigated by isotope exchange technique and it was confirmed that P2O5 strongly disturbs CO2 dissociation. In the present study, the effect of Na2O addition on the rate of CO2 dissociation on the surface of FeOx-Na2O and FeOx-SiO2-Na2O (mol%FeOx : mol%SiO2=65 : 35) melts was measured at 1773 K with PCO2/PCO=1 by isotope exchange technique. Reaction rate constant drastically increased with increasing Na2O content for the FeOx-Na2O system. On the other hand, rate constant gently increased for the FeOx-SiO2-Na2O system. The Fe3+/Fe2+ ratio of each system also slightly increased.To estimate the rate constant from the composition of melts, the relationship between the rate constant and the Fe3+/Fe2+ ratio for the FeOx-CaO-SiO2 system was also investigated. From the comparison of the estimated and observed rate constants, the strong promoting effect of Na2O for CO2 dissociation was confirmed in the FeOx-Na2O system.The surface active effect of Na2O was analyzed by “smoothed surface potential model”, and the nature of molten oxide was discussed. From the obtained values, the surface tension of the molten oxide was estimated as a function of Na2O concentration.