Surface Active Effect of Na₂O on the Rate of CO₂ Dissociation on the Surface of Molten FeO_x-Na₂O and FeO_x-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 FeO_x (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 FeO_x-Na₂O and FeO_x-SiO₂-Na₂O (mol%FeO_x : mol%SiO₂=65 : 35) melts was measured at 1773 K with P_CO2/P_CO=1 by isotope exchange technique. Reaction rate constant drastically increased with increasing Na₂O content for the FeO_x-Na₂O system. On the other hand, rate constant gently increased for the FeO_x-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 FeO_x-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 FeO_x-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.