Surface Composition of Wustite

Abstract

Adsorption I Katalyse I ReaktionskinetikUsing a solid electrolyte cell inside an UHV-system the surface composition of oxides and metals can be studied at high temperatures 700 to 1OOO"C and well defined oxygen activities in the range po, = lo-'' to bar. AES-measurements on wustite have shown that at temperatures >8OO"C the composition of the surface shows the same change with the varied oxygen activity as would be expected for the bulk. At temperatures below 800 "C the change of surface oxygen content is larger than the change of bulk oxygen which indicates the presence of adsorbed oxygen. An adsorption isotherm obtained at 720°C shows that the degree of coverage 0 = 0.07 is approached near the

A comprehensive kinetic model for the CO-CO2 reaction with iron oxide-containing slags

“…Based on the former model, a variation in the oxidation state of the slag may result in the segregation of oxygen ions to the surface, which will, in turn, change the number of available reaction sites for the reaction. The decrease in the reaction rate of CO 2 with several metals [28,29,30] and with solid iron oxide [31] in some conditions has been related to such phenomena. However, Grabke and Viefhaus [31] found that, for solid iron oxide, the excess adsorption of oxygen at the surface takes place only at temperatures below 1073 K. Therefore, it may reasonably be expected that for liquid slags at much higher temperatures, the adsorption is negligible.…”

“…The decrease in the reaction rate of CO 2 with several metals [28,29,30] and with solid iron oxide [31] in some conditions has been related to such phenomena. However, Grabke and Viefhaus [31] found that, for solid iron oxide, the excess adsorption of oxygen at the surface takes place only at temperatures below 1073 K. Therefore, it may reasonably be expected that for liquid slags at much higher temperatures, the adsorption is negligible. The anticipation is in accord with the findings of Kidd and Gaskell [32] and Bhattacharyya and Gaskell, [33] who examined the dependence of surface tension of liquid FeO x on oxygen potential.…”

“…Since, in the oxides, the valence electrons are dominantly localized around the anion core, the molecular polarizability is governed by the polarizability of oxygen (␣ O 2Ϫ ). Consequently, for typical slag constituents, the approximation can be made [40,41] that [31] Substitution from Eqs. [28] and [31] into Eq.…”

Kinetics of CO-CO2 reaction with CaO-SiO2-FeOx melts

“…[58] However, Grabke and Viefhaus [58] found that for wustite, adsorption occurs, only at temperatures lower than 1073 K. The surface structure of oxide melts at high temperature and dependence on oxygen potential has not yet been fully understood. Measurements by Gaskell and his group [59,60] on liquid iron oxide at 1673 K showed that the surface tension of liquid iron oxide is approximately constant with Fe 3ϩ /Fe 2ϩ .…”

“…Grabke and Viefhaus [58] have discussed that dissociation of CO 2 on the surface of solid wustite may involve formation of singly or doubly charged CO 2 ions. Assuming that the introduction of oxygen ions into the iron oxide melt may involve formation of single charge CO 2 ions instead of double charge ions , dissociation of CO 2(ad) can be further broken into two elementary reactions:…”