Oxygen In 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: .

Carbon quantum dots can enable efficient photochemical interfacial activation of molecular oxygen in iron oxides/oxalate system

Photochemical reactions between natural iron oxides and oxalic acid (OA) have attracted wide attentions in environmental decontamination, but the critical interfacial ligand-to-metal charge transfer process (LMCT) is difficult to occur. In this study, carbon quantum dots modified maghemite (γ-Fe2O3/CQDs) with excellent photo-electrochemical properties has been successfully synthesized, which achieved rapid decomposition of sulfamethoxazole (SMX) with OA under UV. It was found that the complexed [≡FeIII(C2O4)n]3-2n on the γ-Fe2O3 surface could occur efficient interfacial LMCT, followed by fast internal transmission of electrons to CQDs part for activating its surface adsorbed O2 to efficiently produce O2•− and •OH. The heterogeneous LMCT would be dominant in UV/γ-Fe2O3/CQDs/OA system for the initial rapid SMX degradation, despite the non-reductive leaching of aqueous FeIII(C2O4)n3-2n would cause additional homogeneous LMCT. Bonded CQDs at iron oxides could highly improve utilization of the photo-generated electrons from complexed OA for O2 activation, and also broaden its application under visible light.

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.

PREPARATION OF MOLTEN CAST IRON FOR MODIFICATION BY MEANS OF REFINING TREATMENT IN THE FURNACE

Refining issues of molten metal are still actual in modern conditions of foundry. In manufacturing process of ductile and vermicular graphite iron castings with required microstructure and mechanical properties one of the essential conditions is the control of sulfur content in the base iron. Increased sulfur concentration (over 0,02%) can destabilize the production process of ductile and vermicular graphite iron castings and decrease the efficiency of modifying treatment. An additional factor reducing the efficiency of modification, which is not mostly controlled and not taken into account in foundry is oxidation of cast iron; average content is 1200–1600 ppb depending on charge materials. In this regard, in the production of ductile castings, the stage of metal pretreatment in the furnace, which consists in refin-ing the metal from sulfur and oxygen, is important. The iron foundry factories do not often have the opportunity to buy the modern equipment for refinement of liquid metal due to its high cost. In this case, in addition to existing traditional methods of refining, it is interesting to use specially developed compositions of complex materials and modifiers, improvement of methods of their input into the liquid metal. A possible variant of metal pretreatment for subsequent modification was presented. The complex briquetted material Refloy®F based on ferrosilicon FS45 has in its composition such active elements as alkaline-earth and rare-earth metals. The chemical composition of briquette Refloy®F and mechanism of its influence on cast iron melt was presented and practical experience of its application was provided. The technology of introducing briquettes depending on applied smelting unit, its consumption characteristics, results of reduction of oxygen and sulfur concentration in pig iron in the course of tests at different plants are presented. The advantages of iron desulfurization technology with Refloy®F briquettes are provided.

Superionic iron alloys and their seismic velocities in Earth’s inner core

Earth's inner core (IC) is less dense than pure iron, indicating the existence of light elements within it1. Silicon, sulfur, carbon, oxygen and hydrogen have been suggested to be the candidates2,3, and the properties of iron-light-element alloys have been studied to constrain the IC composition4-19. Light elements have a substantial influence on the seismic velocities4-13, the melting temperatures14-17 and the thermal conductivities18,19 of iron alloys. However, the state of the light elements in the IC is rarely considered. Here, using ab initio molecular dynamics simulations, we find that hydrogen, oxygen and carbon in hexagonal close-packed iron transform to a superionic state under the IC conditions, showing high diffusion coefficients like a liquid. This suggests that the IC can be ina superionic state rather than a normal solid state. The liquid-like light elements lead to a substantial reduction in the seismic velocities, which approach the seismological observations of the IC20,21. The substantial decrease in shear-wave velocity provides an explanation for the soft IC21. In addition, the light-element convection has a potential influence on the IC seismological structure and magnetic field.

Insights into the tribochemistry of sliding iron oxide surfaces lubricated by sodium silicate glasses: An ab initio molecular dynamics study

Binary alkali silicate glasses are new promising lubricants for harsh working conditions, such as high pressure, elevated temperature, and high sliding speed. In the present work, the tribochemical reaction of sodium silicate under sliding contact with iron oxide substrates was investigated using First Principle Molecular Dynamics. The result indicates that the silicate is chemically active against the iron oxide surface at high temperature. Non-bridging oxygen (NBO) in glass lubricant and iron from the substrate forms the covalent bonds (NBO-Fe), which play a crucial role in the tribological performance. Interestingly, NBO in the glass can change continuously its covalent bond with different Fe atom of the substrate as a consequence of the shearing. Positively charged sodium atoms in the silicate network have an extremely high mobility, which allows them to diffuse towards the substrates, due to the electrostatic interaction with the negatively charged oxygen atoms of iron oxide substrates. These results explain the formation mechanism of a sodium-rich layer on iron oxide substrates. Reducing the sodium content in the glass lubricant will limit the formation of the sodium-rich tribofilm layer and increase the connectivity of the silicate network, which significantly reduce the friction and antiwear properties of the glass lubricant.

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.

Evaluation of metallurgical behavior of oxygen and sulfur in base iron for ductile iron production based on thermal analysis

Evaluation of metallurgical behavior of oxygen and sulfur in base iron for ductile iron production based on thermal analysis

Experimental and ab initio study of the influence of a compound modifier on carbidic ductile iron

To improve the morphology of carbides in carbidic ductile iron, a compound modifier consisting of 0.1% Nb + 0.1% Ti + 0.1 wt.% Y was added to the base ductile iron with chemical composition of 3.72% C, 2.77% Si, 0.51% Mn, 0.99% Cr and balance Fe (wt.%). The effect of this compound modifier on the microstructures of carbidic ductile iron was studied. Also, first-principles calculations were carried out to better understand the modification mechanisms. The results showed that the maximum diameter of spheroidal graphite nodules decreased from 58 to 34 µm after the addition of compound modifier, and continuous carbide networks changed into a broken network. The roundness of graphite nodules decreased slightly, and the percent nodularity of the graphite nodules and the number of carbides decreased by 3 and 1.8%, respectively. Compounds with higher melting point are formed thanks to the compound modifier which acts as heterogeneous core, and the remaining Ti and Nb elements can be selectively attracted by (010) surface of Fe8Cr4C4. Furthermore, Cr elements can be easily replaced by Ti and Nb in the carbides to form more stable Fe8Cr3TiC4 and Fe8Cr3NbC4, which can prevent the continuing growth of carbide on the Fe8Cr4C4 (010) crystal surface and break the continuous network M3C. Y atoms cannot be directly adsorbed onto Fe8Cr4C4 (010) surfaces. They combine first with oxygen in the ductile iron to form Y2O3. The work of adhesion of the interface between a Y2O3 (100) and a Fe8Cr4C3 (010) is predicted to be 0.3 J/m2. The addition of Y element is found to have a positive effect on breaking up the continuity of the carbide network.

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.

Oxygen Solubility in Fe–Co Melts Containing Carbon

In thermodynamic analysis of solutions of oxygen in Fe–Co melts containing carbon, the equilibrium constants of reactions between carbon and oxygen are determined, as well as the activity coefficients at infinite dilution and the interaction parameters in melts of different composition at 1873 K. The dependence of oxygen solubility in such melts on the cobalt and carbon content is calculated. In iron–cobalt melts, carbon has high oxygen affinity. The deoxidizing ability of carbon increase significantly with increase in cobalt content in the melt. In pure cobalt, it is more than an order of magnitude greater than in pure iron. Deoxidation by carbon produces gaseous oxides: carbon monoxide (CO) and dioxide (CO2). The reaction of carbon and oxygen dissolved in the melt and hence the deoxidizing ability of carbon depend on the total gas pressure above the melt. Decrease in gas pressure significantly improves the reducing properties of carbon. The minimum oxygen concentration for alloys of the same composition is reduced by practically an order of magnitude with tenfold decrease in the total gas pressure. The gas composition above Fe–Co melts and the equilibrium carbon and oxygen concentrations in the melt are calculated with total gas pressures of 1.0, 0.1, and 0.01 atm. The optimal oxygen concentration (1–10 ppm) in Fe–Co melts is reached at carbon concentrations between 0.01 and 1% depending on the total gas pressure (0.01–1 atm). The solubility of oxygen in iron–cobalt melts containing carbon passes through a minimum, which is shifted to lower carbon content with increase in the melt’s cobalt content. Further additions of carbon increase the oxygen concentrations in the melt. With increase in cobalt content, this increase will be sharper.

КОМПЛЕКСНАЯ ДЕСУЛЬФУРАЦИЯ И ДЕГАЗАЦИЯ ЧУГУНА МАГНИЕМ

The aim of the work is a theoretical and experimental study of the behavior of oxygen, hydrogen and nitrogen in iron during desulfurization with its granulated magnesium. A computational and analytical assessment of the formation and floating of gas bubbles during the introduction of dispersed magnesium into a metal melt in an argon jet is performed. It has been established by calculation that when dispersed magnesium is introduced into the cast iron in an argon jet, through a lance with a nozzle diameter of 7 mm to a depth of 3 m, argon bubbles with a diameter of 25 mm are formed. The thermodynamic probability of the processes of interaction of magnesium with oxygen, nitrogen and hydrogen during desulfurization of cast iron has been established. It has been established that the processes of desulfurization and deoxidation of iron occur throughout the entire range of pressures under study, and the formation of magnesium nitride is possible only with an excess pressure in the gas-metal system at a depth of molten iron more than 1.4 meters. Experiments in industrial conditions revealed the features of the removal of oxygen, nitrogen and hydrogen from cast iron during desulfurization of the melt with dispersed magnesium in a stream of various carrier gases. It was established experimentally that the type of carrier gas has a decisive influence on the by-pass degassing of the iron during its desulfurization by injecting granular magnesium. When using nitrogen or argon as a carrier gas, the hydrogen content in cast iron is reduced by 50-70%.

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.

Thermodynamic Calculation among Cerium, Oxygen, and Sulfur in Liquid Iron.

Thermodynamic calculation has been applied to predict the inclusion formation in molten SS400 steel. When the Cerium addition in liquid iron is 70 ppm and the initial Oxygen and Sulphur are both 110 ppm, the formation of oxides containing Cerium would experience the transformation from Ce2O3 to CeO2 and also the formation of sulfides containing Cerium would experience the transformation from CeS to Ce2S3 and then to Ce3S4. Below 2000 K the most thermodynamic stable matter is CeO2 and the less thermodynamic stable inclusion is CeS. Only when the amount of [O] is extremely low and the amount of [S] and [Ce] is relatively high, Ce2S3 has the possibility to form.

Thermodynamic Study on Interfacial Reaction between Molten Iron and Spinel

The effect of the oxygen concentration in the molten iron on the formation of the FeO-MgO phase at the interface between the MgAl2O4 spinel substrate and the molten iron was investigated at 1833 K on the basis of thermodynamics. The results showed that the FeO-MgO phase was formed at the interface between the molten iron and the substrate, if the oxygen concentration in the molten iron was larger than 0.04 mass% for the 50mol%Al2O3-50mol%MgO substrate and 0.08 mass% for the 61mol%Al2O3-39mol%MgO substrate, respectively. For both the substrates, with increasing the oxygen concentration in the molten iron, the activity coefficient of FeO in the spinel substrate increased, and when this value reached above 1.5, a part of MgO was discharged from the spinel and reacted with Fe and oxygen in the molten iron to form the FeO-MgO phase.

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.

Sustainability in Metallurgy

Sustainable metallurgical processes encompass new theory and techniques regarding the optimization of existing processes for improved energy efficiency, enhanced environmental benefits, and increased resource/waste/by-product utilization. This special topic, ‘‘Sustainability in Metallurgy,’’ is dedicated to presenting metallurgical processes and related research aimed at improving the sustainability of metal production. For this objective, six articles were collected in this topic, demonstrating how recent progress in metallurgy theory and practice can result in improved sustainability. The sustainable development of metallurgical process must be built on a deep understanding of thermodynamic behavior of related substances. In the first article, which is titled, ‘‘Henry’s Law Activity of Oxygen in Molten Iron,’’ J. W. Matousek proposes a tentative model for evaluation of the thermodynamic behavior of oxygen in molten iron at concentrations below 100 ppm. The findings are deemed a necessary complement to thermodynamics of oxygen in iron as the classic equations were derived in experimental programs in which the oxygen content was above 200 ppm. The traditional blast furnace ironmaking process suffers huge energy consumption, serious environment pollution, and high CO2 emission. Unlike the traditional blast furnace, the oxygen blast furnace exhibits the potential to significantly reduce energy consumption and CO2 emissions. In the second and third articles titled, ‘‘Numerical Study of the Gas Distribution in an Oxygen Blast Furnace. Part 1: Model Building and Basic Characteristics,’’ and ‘‘Numerical Study of the Gas Distribution in an Oxygen Blast Furnace. Part 2: Effects of the Design and Operating Parameters,’’ Zongliang Zhang et al. report the influence of recycling gas distribution from shaft tuyere on heat distribution and energy utilization in oxygen blast furnace by developing a multifluid model. With this model, optimum design and operating parameters of the furnace were achieved, contributing to improved sustainability of the ironmaking process. Biomass char is a renewable resource that can be produced from practically any carbonaceous material, including agricultural and forestry waste. In the fourth article titled, ‘‘Production of LowPhosphorus Molten Iron from High-Phosphorus Oolitic Hematite Using Biomass Char,’’ Huiqing Tang et al. demonstrate the potential of biomass char as a suitable reducing agent for reduction of the hematite to obtain metallic product with low carbon content. The phosphorus content of the product was further reduced in the smelting stage by addition of sodium carbonate. With this approach, hot metal with iron recovery rate of 78% to 75% and phosphorus content of<0.3 wt.% was obtained. For production of nickel pig iron, nickel-bearing resources like nickeliferous laterite ores are often processed using complex energy intensive production routes. To improve the process economics a simple route, namely the blast furnace smelting process, was developed. This process involves a stage of sintering of the mixture of the ore, coke breeze and flux, prior to smelting. In the fifth article titled, ‘‘Evaluation of Sintering Behaviors of Saprolitic Nickeliferous Laterite Based on Quaternary Basicity,’’ Jun Luo et al. show the effect of quaternary basicity on sintering behavior of saprolitic laterite in the reducing atmosphere by controlling the addition of calcium oxide. The sintering indexes, including vertical sintering velocity, yield, and productivity, were improved by optimizing the quaternary basicity. The extraction of gold from complex ores usually involves the use of toxic agents such as cyanides. This will inevitably lead to cyanide contamination of the final process water, which requires further treatment before discharge. The last article in this series by M. Ordiales et al., ‘‘Potassium Zhiwei Peng and Dean Gregurek are the guest editors for the Pyrometallurgy Committee of the TMS Extraction & Processing Division, and coordinators of the topic Sustainability in Metallurgy in this issue. JOM, Vol. 67, No. 9, 2015

Henry’s Law Activity of Oxygen in Molten Iron

A model is proposed for the solubility of oxygen in molten iron in dilute solutions in which the oxygen exists in two states, free and associated. Only the free oxygen has thermodynamic activity in the sense of interaction with an electrochemical cell to produce the voltage described by the Nernst equation.

Vacancy mechanism of oxygen diffusivity in bcc Fe: A first-principles study

Diffusivity of interstitial oxygen (O) in bcc iron (Fe) with and without the effect of vacancy has been investigated in terms of first-principles calculations within the framework of transition state theory. Examination of migration pathway and phonon results indicates that O in octahedral interstice is always energetically favorable (minimum energy) with and without vacancy. It is found that vacancy possesses an extremely high affinity for O in bcc Fe, increasing dramatically the energy barrier (∼80%) for O migration, and in turn, making the predicted diffusion coefficient of O in bcc Fe in favorable accord with experiments.