Effect of Oxidation State of Iron Ions on the Viscosity of Alkali Silicate Melts

Abstract

Understanding the changes in viscosity due to the different oxidation states of iron ions is important for simulating phenomena related to molten slags and also for understanding the structure of iron-oxidecontaining silicate melts. However, these viscosity changes are not well understood. Here, we show the viscosity changes of R2O-SiO2-FexO (R = Li, Na, or K) melts due to changes in the oxidation states of the iron ions by systematically varying the oxygen partial pressure using several Ar-based gases at 1 773 K. The initial compositions of the samples were 30R2O-60SiO2-10Fe2O3 (mol%), and the ratio of Fe 3+ to Fe 2+ in the R2O-SiO2-FexO melts increased with increasing oxygen partial pressure in all samples. Meanwhile, the viscosity of all the R2O-SiO2-FexO melts decreased with increasing Fe 2+ to total-Fe ratio. The data indicate that the increase in the amount of Fe 2+ ions, which behave as network modifiers, would result in depolymerization of the silicate melts. It should also be noted that the viscosity of the melts increased in the order of alkali cationic radius (K > Na > Li) when the ratios of Fe 2+ to Fe 3+ in the melts were comparable. This was due to the change in the coordination structure of Fe 3+ in the melts. Not only the oxidation state of the iron ions but also the coordination structure of Fe 3+ may be important for understanding the viscosity.KEY WORDS: viscosity; alkali ferrosilicate melts; redox equilibria of Fe; oxygen partial pressure.

Structural Evolution of Molten Slag during the Early Stage of Basic Oxygen Steelmaking

“…18) In order to make the value of Fe 3 + /Fe 2 + within this range, a suitable oxygen partial pressure must be taken into account. Based on previous study, 20) it is found that when the value of Fe 3 + /Fe 2 + was between 0.13 and 0.16 at 1 773 K in the R-Si-Fe-O system (R = K or Na), oxygen partial pressure was approximately 10 − 10 atm. The Ca-Si-Fe-O system in this study is similar to the above system, so the oxygen partial pressure in our experiment can be designed in terms of R-Si-Fe-O system.…”

“…The researches indicated that the iron redox state was as a function of pressure, temperature and bulk composition. 13,20) Under the same condition of other factors, the Fe 3+ / Fe 2+ ratio decreased with increasing ionic potential (Z/r) of non-framework cations and had positive correlation with oxygen partial pressure. 13,18) The Z/r of K + , Na + and Ca 2+ is 0.75, 1.02, 2.00, respectively.…”

Arrhenius Crossover Phenomena and Ionic Conductivity in Ionic Glass‐Forming Liquids

“…This process is related with the structural relaxation ( α relaxation) seen in the glass‐formation process. [ 1–3,27,28 ] In the supercooled liquid state below T m , the viscous flow occurs due to breaking and switching the bonds connecting the structural units (or molecular units). Likewise, bond twisting can also trigger the flow of adjacent structural units.…”

Crystallization Behaviors of Spinel During Cooling Process of Modified EAF Slag

“…Stage three involves the crystallization of the DS and the solidification with a silicate glassy phase from this homogeneous melt. Osugi et al [25] reported that the oxidation state of iron ions, and the coordination structure of Fe 3+ had a great influence on the viscosity of the melt. Fe 3+ plays an intermediate role between the network former and the network modifier since it forms both tetrahedra [FeO 4 ] and octahedra [FeO 6 ].…”