Oxygen In Liquid Iron Research Articles

Assessment of Equilibrium between Yttrium and Oxygen in Liquid Iron

Rare earth elements (REEs) are crucial additives in the iron and steel industry. The accurate determination of thermodynamic data is fundamental for applying REEs in steel production; however, this has proven challenging due to their strong reactivity with refractory materials. This study assessed the thermodynamic data for the yttrium–oxygen equilibrium in liquid iron, using high‐temperature experiments with high‐purity Y2O3 crucibles as the smelting container. More reliable equilibrium constants and first‐order interaction coefficients are obtained by minimizing the reactions between yttrium and the crucible while ensuring favorable kinetic conditions. The results confirm that the deoxidation product of yttrium in liquid iron is Y2O3, and the equilibrium constant for the reaction Y2O3(s) = 2[Y] + 3[O] can be expressed as follows: . can be expressed as: . The first‐order interaction coefficient can be presented as: .

Y2O3‒SiO2 SYSTEM DIAGRAM

The deoxidizing ability of yttrium has not been sufficiently studied, although it has a high affinity for oxygen. In ferrous metallurgy, yttrium is often used in the form of an alloy with silicon. The effect of each of the components of the silicoyttrium alloy on the process of liquid metal deoxidation can be established by studying the Fe‒Y‒Si‒O system. The composition of the formed non-metallic inclusions in steel in this case is mainly determined by the type of oxide state diagrams of the Y2O3‒SiO2 and FeO‒Y2O3‒SiO2 systems associated with the region of existence of metallic melts. In this work, using the method of thermodynamic modeling of phase equilibrium in oxide system state diagrams and the theory of subregular ionic solutions, we analyze and calculate liquidus lines in the Y2O3‒SiO2 oxide system. A diagram of the state of this system was constructed. According to the thermodynamic analysis, the most stable in the system are three compounds ‒ oxy- Y2O3·SiO2 and yttrium orthosilicate 2Y2O3·3SiO2 (congruent melting, 1979 and 1915 °C, respectively), as well as yttrium pyrosilicate Y2O3·2SiO2 (incongruent melting), which is consistent with the literature data. In the course of the work, the enthalpies and entropies of formation of these yttrium silicates from the components of the oxide melt, as well as the melting constants of these compounds, were obtained. The area of delamination borders on the field of cristobalite at 1668 °C in the concentration range 0.593‒0.980 (ionic fraction of SiO2) or 74.5‒99.0 % (mol.) SiO2. The values of the enthalpy and entropy of yttrium silicates obtained in this work allow us to proceed to the next stage of the study – modeling the state diagram of the ternary oxide system FeO‒Y2O3‒SiO2, which is necessary to consider the interaction of yttrium and silicon with oxygen in liquid iron.

Thermodynamic analysis of deoxidizing ability of strontium in liquid iron: phase stability diagram IN Fe-Sr-O and Fe-Mg-Sr-O systems

Strontium is considered to be a promising element-deoxidizer and a modifier of steels and alloys, especially in barium and calcium-containing alloys. However, the thermodynamics of its interaction with oxygen in liquid iron is not studied enough. The aim of the study is a thermodynamic analysis of the deoxidizing ability of strontium in liquid iron of the Fe-Sr-O and Fe-Mg-Sr-O systems using a method for constructing the surface of the solubility of components in a metal (SSCM). SSCM is a diagram linking the compositions of a liquid metal with the compositions of the products of interaction formed during deoxidizing. At the calculation, the chemical reactions occurring in the melt of the Fe-Sr-O and Fe-Mg-Sr-O systems and the equilibrium constants of these reactions, including the formation of liquid and solid strontium oxides from the components of the metal melt, were established. The first-order interaction parameters (according to Wagner) of strontium with oxygen and magnesium in liquid iron were determined. The oxygen solubility isotherms were constructed in the Fe-Sr-O systems (within the temperature range 1550-1650 °С) and FeMg-Sr-O (for the temperature 1600 °С). The maximum deoxidizing ability of strontium in liquid iron was determined. It was established that in comparison with magnesium, strontium is a weaker deoxidizer.

Thermodynamics of the Interactions in Fe–Mg–Al–La–O Melts

Today, rare-earth elements are mainly introduced in alloys in the form of misch metal, which is a natural mixture of rare-earth elements (with atomic numbers 57–71). This mixture contains about 50 wt % cerium. The primary components of the mixture are generally cerium, lanthanum, and niobium. The specific composition depends on the particular field from which they were drawn. The variable composition of this mixture may significantly impair its effectiveness in alloying. The ratio of the individual elements in the mixture cannot be determined experimentally for each grade of steel, because of the prohibitive expense of such separation. However, thermodynamic modeling permits determination of the optimal concentration of each rare-earth element and the composition of the misch metal. In the present work, thermodynamic modeling is applied to the interaction of magnesium, aluminum, and lanthanum with oxygen in liquid iron. The thermodynamic model of the reduction of steel by mixtures of such active metals is considered. On the basis of literature data regarding the phase diagrams of the MgO–Al2O3, MgO–La2O3, and La2O3–Al2O3 systems, the coordinates of points of invariant equilibrium in the MgO–La2O3–Al2O3 system are established. The MgO–La2O3–Al2O3 phase diagram is plotted. That permits the identification of all possible equilibria in the reduction of steel by magnesium, aluminum, and lanthanum and also the determination of corresponding descriptive equations. The activity of the components in liquid oxide melts is determined by the theory of subregular ionic solutions, taking account of the influence of the oxide melt’s composition on the coordination number of the cations. The activity of the components in metallic melts that are conjugate with the oxide systems is determined by means of the Wagner theory on the basis of first-order reaction parameters. The equilibrium constants of the reduction of steel by the given elements are established by indirect thermodynamic calculations. On the basis of the results, the solubility surface of the components in Fe–Mg–Al–La–O melts is constructed. That permits the identification of regions where the composition of the liquid metal corresponds to a particular oxide phase.

Structural changes and anomalous self‐diffusion of oxygen in liquid iron at high pressure

AbstractWe report structural properties and diffusivity of liquid Fe0.96O0.04 over a density range of 5.421–11.620 g cm−3, corresponding to pressures of 0–330 GPa and 2200–5500 K, using first‐principles molecular dynamics. We predict a change in compression mechanism near 8 g cm−3. At lower density, Fe and O coordinations increase from ~10 to ~13 and ~3 to ~6, respectively, the average Fe–O distance increases from ~1.81 Å to ~1.88 Å, and the Fe–Fe distance remains essentially constant. Calculated oxygen diffusivities, DO, remain constant over the corresponding pressure range, consistent with experiments. For larger densities, interatomic distances and diffusion rates for both species decrease monotonically. Oxygen coordination reaches a maximum of ~8.5 at ~9.4 g cm−3, indicating a local B2 packing for Fe around O under conditions of the Earth's core. The pressure‐induced structural evolution provides an explanation for a previously reported change in pressure dependence of oxygen solubility in liquid iron.

On the Interaction of Calcium and Oxygen in Liquid Iron

The parameters of calcium and oxygen interaction in liquid iron are revised. The Vagner parameter values of several hundreds or dozens are proved to be wrong. The recommended value for the constant for the reaction of dissolved calcium and oxygen forming solid calcia is /CaO/=[Ca]+[O] is: lgK/CaO/=-34100/T + 13.46. Vagner parameter for the interaction of Ca and O in liquid iron should be expressed in units (we used =–1.41), not in hundreds. The equilibrium diagram of calcium and oxygen content in liquid iron is calculated at 1550-1700 °C and 0.00001-0.1 mass % Ca. The minimum oxygen content possible to be achieved at 1550 °C and 1 atm is about 0.001 mass %.

Critical Assessment and Thermodynamic Modeling of the Al-Fe-O System

A complete literature review, critical evaluation, and thermodynamic modeling of the phase diagrams and thermodynamic properties of phases in the Al-Fe-O system at 1 atm total pressure are presented. Optimized model equations for the thermodynamic properties of all phases are obtained, which reproduce all available thermodynamic and phase-equilibrium data within experimental error limits from 298.15 K (25 °C) to above the liquidus temperatures at all compositions and oxygen partial pressures from metal saturation to 1 atm. The complex phase relationships in the system have been elucidated, and discrepancies among the data have been resolved. The database of the model parameters can be used along with software for Gibbs-energy minimization in order to calculate all thermodynamic properties and any type of phase diagram section. The modified quasichemical model was used for the liquid oxide phase. A sublattice model, based upon the Compound Energy Formalism, was developed for spinel, which expands from magnetite, Fe3O4, to hercynite, FeAl2O4. The distribution of cations between octahedral and tetrahedral sites and oxygen nonstoichiometry in spinel are taken into account. The model for metallic liquid assumes random mixing of associates: Fe, Al, O, AlO, and Al2O. It describes well the minimum that is observed on the solubility of oxygen in liquid iron as a function of the Al content. The solid solution between hematite and corundum exhibiting a miscibility gap, as well as a small solubility of Al2O3 in wustite are quantitatively described by a simple Bragg-Williams model.

An Improved Theoretical Model for A-TIG Welding Based on Surface Phase Transition and Reversed Marangoni Flow

It is experimentally shown that a thin layer of silica flux leads to an increased depth of weld penetration during activated TIG (=A-TIG) welding of Armco iron. The oxygen-content is found higher in the solidified weld metal and it is linked to the increased depth of penetration through the reversed Marangoni convection. It is theoretically shown for the first time that the basic reason of the reversed Marangoni convection is the phenomenon called “surface phase transition” (SPT), leading to the formation of a nano-thin FeO layer on the surface of liquid iron. It is shown that the ratio of dissolved oxygen in liquid iron to the O-content of the silica flux is determined by the wettability of silica particles by liquid iron. It is theoretically shown that when the silica flux surface density is higher than 15 µg/mm2, reversed Marangoni flow will take place along more than 50 pct of the melted surface. Comparing the SPT line with the dissociation curves of a number of oxides, they can be positioned in the following order of their ability to serve as a flux for A-TIG welding of steel: anatase-TiO2 (best)-rutile-TiO2 (very good)-silica-SiO2 (good)-alumina-Al2O3 (does not work). Anatase (and partly rutile) are self-regulating fluxes, as they provide at any temperature just as much dissolved oxygen as needed for the reversed Marangoni convection, and not more. On the other hand, oxygen can be over-dosed if silica, and other, less stable oxides (such as iron oxides) are used.

Partitioning of Si and O between liquid iron and silicate melt: A two‐phase ab‐initio molecular dynamics study

The magma ocean process in the early history of the Earth has a great influence on the light element identities and contents of the core which subsequently affect the energy of the geodynamo provided by the compositional convection and the inner core growth through their effect on the phase diagram of iron alloy. In the present work, a two‐phase ab‐initio molecular dynamics method is established to study the solubility of silicon and oxygen in liquid iron in equilibrium with silicate melt. The ab‐initio results are found to be in close agreement with experimental data. At the base of a deep magma ocean (39 GPa and 3116 K), liquid iron contains 2.7 wt% silicon and 0.5 wt% oxygen at the current bulk Earth composition. The oxygen content is low compared with its current estimate in the core, indicating a deeper magma ocean may need to be invoked.

Assessment of thermochemical data on steel deoxidation

It is proposed to develop a method to judge the certainty on the information regarding to deoxidation equilibria of iron melts. To accomplish this objective, thermochemical data was collated and then evaluated. The basic knowledge on deoxidation conditions are framed by the non-ideal Henrian behaviour of diluted solutions of both deoxidizer and oxygen in liquid iron in equilibrium with a pure oxide. Conventional deoxidation reactions were considered at 1,873 K such that in their equilibrium constants, only first order interaction coefficients were considered. The criteria in selecting the most appropriated free energy equation was based on evaluating them under two critical composition points: 1 where they satisfy an oxygen to deoxidizer ratio dictated by its stoichiometry and 2 where oxygen contents at a given amount of deoxidizer reaches a minimum value. These data were plotted on logarithmic scales to appreciate the effects of deoxidizer’s valences. Once such information was classified, under restrictions 1 and 2, previous compositions were related to deoxidizer´s electronegativities.

Interfacial Tension between CaO‐Al2O3 Slag and Iron Containing Nonmetal or Tramp Elements

The interfacial tension between CaO‐Al2O3 slag and iron was studied for the iron containing nonmetal or tramp elements. The sessile drop technique was used to measure interfacial tensions under argon atmosphere at 1853K. Oxygen in liquid iron markedly reduced the interfacial tension. This effect was taken into consideration when analysing the interfacial tension between the slag and Fe‐S, Fe‐C, Fe‐Sn, Fe‐Sb and Fe‐Cu alloys. When adding S, Sn, Sb, or Cu to the iron, the interfacial tension was observed to decrease while carbon had no significant effect.

Influence of Slag Composition on Slag–Iron Interfacial Tension

Interfacial tensions between liquid iron and slag were examined for CaO–SiO2 binary and CaO–SiO2–Al2O3 ternary slag systems. The influences of FeO, MgO, B2O3, TiO2, BaO and ZrO2 in slag on the interfacial tension were also investigated by varying these oxides from 1–30 wt% in the CaO–SiO2 binary or CaO–SiO2–Al2O3 ternary slag systems.The interfacial tensions were determined by the sessile drop technique under argon atmosphere at 1 853 K. An X-Ray radiographic technique was employed to image the profile of molten iron drop in a slag bath and the interfacial tensions between slag and iron were obtained from the drop shape analysis.In examining the effect of slag composition on the interfacial tension, the oxygen in liquid iron and its impact on the interfacial tension was taken into consideration. The interfacial tension was found slightly increased with increasing CaO/SiO2 ratio in CaO–SiO2 slag, and with increasing MgO content in the slag. A decrease of interfacial tension was found with increasing FeO in slag. Only minor changes in the interfacial tension were observed with varying the slag composition in the CaO–SiO2–Al2O3 ternary slag system and the influences of B2O3, TiO2, BaO, and ZrO2 in slag on the interfacial tension were found insignificant.

Marangoni convection and weld shape variations in Ar–O2 and Ar–CO2 shielded GTA welding

Increasing the oxygen or the carbon dioxide concentration in the argon-based shielding gas leads to an increase in the weld metal oxygen content when the oxygen or carbon dioxide concentration is to be lower than 0.6 vol.% in the shielding gas. However, when the O2 or CO2 concentration is higher than 0.6 vol.% in the Ar-based shielding gas, the weld metal oxygen is maintained around 200 ppm–250 ppm. An inward Marangoni convection mode in the weld pool occurs when the weld metal oxygen content is more than 100 ppm. When it is lower than 100 ppm, the Marangoni convection would change to the outward direction and the weld shape varies from a deep narrow to a shallow wide shape. The effective ranges of O2 and CO2 concentrations for deep penetration are same. A heavy layer of oxides is formed when the O2 or CO2 concentration in the shielding gas is more than 0.6 vol.%. Based on the thermodynamic calculation of the equilibrium reactions of Fe, Si, Cr and Mn with oxygen in liquid iron for the oxide products, FeO, SiO2 ,C r 2O3 and MnO and the experimental oxygen content in the weld metal, Cr2O3 and SiO2 oxides are possibly formed at the periphery area of the liquid pool surface under the arc column during the welding process. One model is proposed to illustrate the role of the oxide layer on the Marangoni convection on the pool surface at elevated temperature. The heavy oxide layer inhibited the fluid flow induced by the Marangoni convection and also became a barrier for the oxygen absorption into the molten weld pool. © 2004 Elsevier B.V. All rights reserved.

Thermodynamics of nucleation and supersaturation for the aluminum-deoxidation reaction in liquid iron

The nucleation process of alumina in aluminum-deoxidized liquid iron was investigated by computer simulation, in which the Gibbs free-energy change of the parent liquid iron, the dependence of interfacial free energy between liquid iron and α-alumina on oxygen content, and the dependence of the interfacial free energy on the curvature of a nucleus were considered. The calculated curve of the Gibbs free-energy change of the systems (ΔG), with respect to nuclear radius, has a maximum and a minimum. Nucleation occurs rapidly when the initial oxygen content is higher than the critical point of nucleation (C O ), but the growth of nuclei stops just after ΔG reaches its minimum. At the minimum, the small alumina nuclei are suspended in liquid iron for an extended period of time. This suspension is one reason for the presence of excess oxygen in liquid iron above the α-alumina equilibrium level, which is characteristic in this system. The residual dissolved aluminum and oxygen at the ΔG minimum remain supersaturated in the liquid iron. At an initial oxygen content below C 0 , no nucleation can occur, and the components in the liquid iron remain in the supersaturated state. This supersaturation is another reason for the phenomenon of excess oxygen in liquid iron.

Equilibria of Ce‐Al‐O and Nd‐Al‐O in molten iron

Equilibrium of Ce‐Al‐O or Nd‐Al‐O system in molten iron was studied by separately melting radioactive isotope 141Ce or 147Nd in an Al2O3 crucible filled with pure iron to form 141CeAlO3 or 147NdAlO3 around its inner wall. The content of dissolved Ce or Nd in iron was determined by means of electrolysis in anhydrous electrolyte and radioassay. The concentration of dissolved Al in iron was obtained by photometry and followed by calculation. Activity of oxygen in liquid iron was directly measured by solid electrolyte sensors made of ZrO2(MgO) tube. By extrapolation of data obtained, the temperature dependence of the equilibrium constant of RE‐Al‐O in molten iron, , or of interaction coefficient, may be described as: urn:x-wiley:01774832:srin01171:equation:srin01171-math-0001

Equilibrium between Yttrium and Oxygen in Liquid Iron and Nickel.

In order to investigate the equilibrium between yttrium and oxygen in liquid iron and nickel, the deoxidation equilibrium of yttrium in liquid iron and nickel saturated with yttria has been measured at the temperature ranges from 1600 to 1700°C using the sampling technique.The equilibrium constant for the deoxidation reaction: Y2O3(s)=2Y+3O in liquid iron was found to be:logKY(Fe)(KY(Fe)=aY2aO3/aY2O3)=–36160/T+7.33 1600–1700°Cwhile the deoxidation product, K'Y(Fe)(=[%Y]2[%O]3) was expressed as follows: logK'Y(Fe)=logKY(Fe)–(–17350/T+3.14)(3[%Y]+11.1[%O]) 0.02<[%Y]<0.11 by the use of the interaction parameter, eO(Fe)Y=–17350/T+3.14. The equilibrium constant for the deoxidation of liquid nickel, log KY(Ni), was determined as the expression: logKY(Ni)=–36250/T+6.36 1600–1700°C Besides, the deoxidation product of nickel was represented to be: logK'Y(Ni)=logKY(Ni)+6.47(3[%Y]+11.1[%O]) 0.01<[%Y]<0.11 with the interaction parameter, eO(Ni)Y=–6.47 at the temperature between 1600 and 1700°C.

Assessment of Calcium-Oxygen Equilibrium in Liquid Iron.

The first-order (eOCa) and the second-order (rOCa, rOCa, O) interaction parameters between calcium and oxygen in liquid iron were determined at 1873 K by using the previous data obtained in slag-metal equilibrium experiments, on the basis of the reciprocal and conversion relationships between mass percent and mole fraction scales. The Values for eOCa, rOCa and rOCa, O were obtained as -3600, 5.7×105 and 2.9×106 in the range of {[mass%Ca]+2.51[mass%O]}<0.005 and -990, 4.2×104 and 2.1×106 in the range of {[mass%Ca]+2.51[mass%O]}≥0.005, respectively, and the validity of these values was discussed.

溶融鉄およびニッケル中のイットリウムと酸素の平衡

溶融鉄およびニッケル中のイットリウムと酸素の平衡

Wettability of Al&lt;SUB&gt;2&lt;/SUB&gt;O&lt;SUB&gt;3&lt;/SUB&gt; Substrate by Liquid Iron &lt;BR&gt;&amp;mdash;Effects of Oxygen in Liquid Iron and Purity of Al&lt;SUB&gt;2&lt;/SUB&gt;O&lt;SUB&gt;3&lt;/SUB&gt; Substrate&amp;mdash;

The interfacial properties between liquid Fe-O alloy and alumina substrates with different purities, 99.9% and 96% Al 2 O 3 , were measured by the sessile drop method. The interfaces of samples were examined by SEM and EPMA after the experiment. It was found that the surface tension decreased with increasing oxygen concentration in the iron for both substrates. The contact angle of 99.9% Al 2 O 3 abruptly increased with increasing oxygen concentration at lower oxygen concentrations. These phenomena were attributed to the dissociation of Al 2 O 3

溶鉄の表面張力およびアルミナとのぬれ性におよぼす酸素の影響

The surface tension and the contact angle of liquid iron on the alumina substrate were measured at 1823 K over a wide range of oxygen concentration in the iron by the sessile drop method under the condition of oxygen transfer from the gas phase to liquid iron (3.8×10−6 mol/m2s).It was presumed from the considerations of time-dependence of surface tension and the increasing rate of oxygen in liquid iron that the adsorption reaction at the liquid iron surface should be nearly in equilibrium with oxygen in liquid iron under the rate of oxygen transfer in the present study.From the Gibbs adsorption isotherm, the excess quantities for oxygen at the liquid iron surface and the interface between liquid iron and alumina substrate were calculated as 2.1×10−5 mol/m2 and 2.4×10−5 mol/m2, respectively. The excess quantity for oxygen at the liquid iron surface is in good agreement with those obtained by previous investigators under the assumption of adsorption equilibrium of oxygen at the surface.The relation between the surface tension, γlg (N/m), and the oxygen activity in the liquid iron is given by the following equation:(This article is not displayable. Please see full text pdf.) \ oindentThe contact angle of liquid iron on the alumina substrates decreases with increasing oxygen content in the iron. The work of adhesion increases with increasing oxygen content up to 0.03 mass%, while above 0.03 mass%, it increases very gradually with increasing oxygen content. FeO·Al2O3 was detected at the interface for the high oxygen level.