Deoxidation equilibria of calcium and magnesium in liquid iron

Calcium-oxygen and magnesium-oxygen equilibria in liquid iron saturated with CaO-SiO₂-Al₂O₃-MgO slags were studied at 1873 K using CaO, Al₂O₃, and MgO crucibles. The applicability of the first-order and second-order interaction coefficients between Ca and O and between Mg and O was studied by comparing the Ca-O and Mg-O equilibria observed in the present and previous experiments with the calculated ones from the respective interaction coefficients. As a result, the interaction coefficients obtained in the present work by using a new method were found to explain the measured solubilities of CaO and MgO. The phase stability region in Fe-Al-M (M=Ca, Mg)-O system was described at 1873 K.     

On the minimum in the deoxidation equilibrium curve in liquid iron oxide Fe-O-M alloys

Abstract

The minima in the equilibrium deoxidation curves of Fe-Q-M systems at steelmaking temperatures are discussed in a quantitative manner in terms of a first order interaction parameter model. Two criteria for a minimum are developed and applied to the prediction of the position of minima in the deoxidation curves of several systems, including the system Iron-Oxygen-Rare Earth.

Résumé

Les minima dans les courbes de désoxydation des systèmes Fe-O-M aux températures élevées sont interprétés de façon quantitative au moyen d'un modèle utilisant des paramètres d'interaction du premier ordre. Les auteurs présentent deux critères qui déterminent la position des minima et les appliquent à plusieurs systèmes, et en particulier, au système Fer-Qxygène-Terres Rares.

a : Raoultian activity

f : Henrian activity coefficient

h : Henrian activity

e_i,j : interaction parameter of element j on element i.

K: equilibrium constant of deoxidation reaction

%M : weight per cent metal in solution

%O : weight per cent oxygen in solution

%M* : weight per cent metal in solution at minimum point

%O* : weight per cent oxygen in solution at minimum point

x,y : stoichiometric coefficients

C : log₁₀ e ? 0.4343     

Galvanic cell measurements on supersaturated activities of oxygen in Fe-Al-M (M=C, Te, Mn, Cr, Si, Ti, Zr, and Ce) melts

Using a mullite (3Al₂O₃ · 2SiO₂)-tube and ZrO₂-9 mol pct MgO-plug type solid electrolyte galvanic cells, the activities of supersaturated oxygen in Fe-0.0017 to 0.41 mass pct Al-M (M=C, Te, Mn, Cr, Si, Ti, Zr, and Ce) alloys were measured as a function of total Al or M contents at 1873 K in an alumina crucible. Based on these results, the effects of alloying elements on the supersaturated oxygen activity with respect to alumina precipitation were studied. In the Fe-Al-M (M=C, Te, Mn, Cr, and Si) alloys, the supersaturated oxygen activities for a given Al level approach the equilibrium values with increasing contents of alloying elements. However, the oxygen activities for a given Al level are still supersaturated in the Fe-Al-M (M=Ti, Zr, and Ce) alloys even in the presence of considerable amounts of the alloying elements.     

Activities in CaO-SiO2-Al2O3 slags and deoxidation equilibria of Si and Al

By using the data in previous and present slag-metal equilibrium experiments, the activities of SiO₂ along the liquidus lines in CaO-SiO₂-Al₂O₃ slags were determined at 1823 and 1873 K from the reaction Si+2O=SiO₂ (s), in which the oxygen activities were estimated from the measured oxygen contents or from the combination of nitrogen distribution ratios (L _N) and nitride capacities (C _N). The activities of Al₂O₃ were also determined from the reaction 2Al+3O=Al₂O₃ (s), in which the oxygen activities were estimated from the values for L _N and C _N, or from the reaction 3SiO₂ (s)+4Al=2Al₂O₃ (s)+3Si, in which the activities of SiO₂ and the contents of Al and Si along with the respective interaction coefficients were used. The activities of Al₂O₃ and CaO in the entire liquid region were estimated from the Rein and Chipman’s activities of SiO₂ by using the method of Schuhmann. On the basis of these activities, the deoxidation equilibria of Si and Al in steels were discussed.     

The activity of calcium in calcium-metal-fluoride fluxes

The standard Gibbs energy of reaction Ca (1) +O (mass pct, in Zr) = CaO (s) has been determined as follows by equilibrating molten calcium with solid zirconium in a CaO crucible: ΔG° = -64,300(±700) + 19.8(±3.5)T J/mol (1373 to 1623 K) The activities of calcium in the CaO_satd-Ca-MF₂ (M: Ca, Ba, Mg) and CaO_satd-Ca-NaF systems were measured as a function of calcium composition at high calcium contents at 1473 K on the basis of the standard Gibbs energy. The activities of calcium increase in the order of CaF₂, BaF₂, and MgF₂ at the same calcium fraction of these fluxes. The observed activities are compared with those estimated by using the Temkin model for ionic solutions. Furthermore, the possibility of the removal of tramp elements such as tin, arsenic, antimony, bismuth, and lead from carbon-saturated iron by using calcium-metal-fluoride fluxes is discussed. Formerly Graduate Student, Department of Metallurgy, The University of Tokyo.     

Thermodynamic assessment of Mg deoxidation reaction of liquid iron and equilibria of [Mg]‐[Al]‐[O] and [Mg]‐[S]‐[O]

The deoxidation reaction of magnesium was investigated thermodynamically employing the equilibrium system between magnesium vapour and liquid iron in the molybdenum chamber sealed with an iron cover at 1873 K as a fundamental study to address the clean steel production technology in the steelmaking process. The previously reported thermodynamic data for magnesium deoxidation reaction are limitedly in good agreement with only their respective specific Mg concentration range, but fail to explain the thermodynamic equilibria generally over the wider range of magnesium concentration beyond the limited range. Therefore, the equilibrium constant, K_Mg for the magnesium deoxidation reaction as well as the first and second‐order interaction parameters between magnesium and oxygen were determined over the extensive magnesium mass content range covering up to 0.04 %. Furthermore, the phase stability diagram based on the equilibria of [Mg]‐[Al]‐[O] in liquid iron for the purpose of controlling the oxide inclusions in the steelmaking process was accomplished using the determined thermodynamic parameters. The equilibria of [Mg]‐[S]‐[O] were also discussed in order to evaluate the utilisation of Mg as a desulphurizing agent as well as deoxidizer in the production process of low carbon steels.     

Thermodynamics on the formation of spinel (MgO·Al<Subscript>2</Subscript>O<Subscript>3</Subscript>) inclusion in liquid iron containing chromium

The stability diagram of MgO, spinel solid solution (MgO·(Al _X Cr_1−X )₂O₃), and sesquioxide solid solution ((Al _Y Cr_1−Y )₂O₃) as a function of Mg, Al, and O contents at a constant chromium content (18 mass pct) in liquid iron is drawn at 1873 K. The interaction parameters between Mg and other solutes (Al, Cr, Ni, Ti, Si, and C) are determined by the experimental method, which assures equilibrium between Mg vapor and liquid iron, were applied to calculate the diagram. Titanium deoxidation is not recommended for the prevention of spinel formation, because Ti accelerates Mg dissolution from refractory or slag due to its high affinity for Mg (e _Mg ^Ti = − 0.64). The standard Gibbs free energies of formation for the three inclusions (periclase, spinel, and sesquioxide solid solutions) and the tielines between two solid solutions were calculated with the aid of the regular solution model and the thermochemical F*A*C*T database computing system, respectively. The phase stability regions and oxygen content in steel for the current Fe-Mg-Al-Cr (18 mass pct)-O system are compared with those of the previous non-Cr system. Detailed information on the spinel composition according to Mg and Al contents is also available from the present stability diagram.     

Modification of Inclusions in Liquid Iron by Mg Treatment

Effect of Mg addition on the compositions of inclusions were studied. The results show that Mg can minimize the inclusions of steel obviously. Under the present condition, Mg deoxidation products of low-S content experimental steel would be changed in the order of Al₂O₃→MgAl₂O₄→Mg→Al–O–S→Mg–O–S. Mg deoxidation products of high-S content experimental steel generate Mg–S(–O)+MnS type inclusions, except for usual oxysulfide. And it is consistent with the results of thermodynamics calculation. Mg is preferred to react with oxide, compared with sulfide. The reaction reaches the equilibrium after 1 min or 5 min. It shows that the number and diameter of inclusions in all experimental steel samples are well under control, helping to improve the properties of steel.     

Modification and Minimization of Spinel(Al<Subscript>2</Subscript>O<Subscript>3</Subscript>·<Emphasis Type="Italic">x</Emphasis>MgO) Inclusions Formed in Ti-Added Steel Melts

High-melting-point inclusions such as spinel(Al₂O₃·xMgO) are known to promote clogging of the submerged entry nozzle (SEN) in a continuous caster mold. In particular, Ti-alloyed steels can have severe nozzle clogging problems, which are detrimental to the slab surface quality. In this work, the thermodynamic role of Ti in steels and the effect of Ca and Ti addition to the molten austenitic stainless steel deoxidized with Al on the formation of Al₂O₃·xMgO spinel inclusions were investigated. The sequence of Ca and Ti additions after Al deoxidation was also investigated. The inclusion chemistry and morphology according to the order of Ca and Ti are discussed from the standpoint of spinel formation. The thermodynamic interaction parameter of Mg with respect to the Ti alloying element was determined. The element of Ti in steels could contribute to enhancing the spinel formation, because Ti accelerates Mg dissolution from the MgO containing refractory walls or slags because of its high thermodynamic affinity for Mg ( e_\textMg^\textTi = - 0. 9 3 3). ( {e_{\text{Mg}}^{\text{Ti}} = - 0. 9 3 3}). Even though Ti also induces Ca dissolution from the CaO-containing refractory walls or slags because of its thermodynamic affinity for Ca ( e_\textCa^\textTi = - 0.119 ), \left( {e_{\text{Ca}}^{\text{Ti}} = - 0.119} \right), dissolved Ca plays a role in favoring the formation of calcium aluminate inclusions, which are more stable thermodynamically in an Al-deoxidized steel. The inclusion content of steel samples was analyzed to improve the understanding of fundamentals of Al₂O₃·xMgO spinel inclusion formation. The optimum processing conditions for Ca treatment and Ti addition in austenitic stainless steel melts to achieve the minimized spinel formation and the maximized Ti-alloying yield is discussed.     

Inclusion control of ferritic stainless steel by aluminum deoxidation and calcium treatment

A thermodynamic equilibrium between aluminum and oxygen and inclusion morphology in the Fe-16Cr stainless steel were investigated to understand the fundamentals of the aluminum deoxidation technology for ferritic stainless steels. Further, the effect of calcium addition on the changes in chemistry and morphology of inclusions was discussed. The measured results for the aluminum-oxygen equilibria exhibit relatively good agreement with the calculated values, indicating that an introduction of the first-and second-order interaction parameters, recently reported, is reasonable to numerically express the aluminum deoxidation equilibrium in a ferritic stainless steel. In the composition of dissolved aluminum content greater than about 60 ppm, pure alumina particles were observed, while the alumino-manganese silicates containing Cr₂O₃ appeared at less than 20 mass ppm of dissolved aluminum. The formation of calcium aluminate inclusions after Ca treatment can be discussed based on the thermodynamic equilibria among calcium, aluminum, and oxygen in the steel melt. In the composition of steel melt with relatively high content of calcium and low aluminum, the log ( ) of inclusions linearly increases by increasing the log [a _Ca/a _Al ² ·a _O ² ] with the slope close to unity. However, the slope of the line is significantly lower than the expected value in the composition of steel melt with relatively low calcium and high aluminum contents.     

Thermodynamics of O,N, and S in liquid Fe equilibrated with CaO-AI2O3-MgO slags

Nitrogen and S distribution ratios between CaO-Al₂O₃-MgO slags and liquid Fe were measured at 1873 K as a function of Al (or Mg, Ca) content in metal, using CaO, MgO, and A1₂O₃ crucibles. Based on the results for the solubility product of MgO, the equilibrium constant,K _Mg , for the reaction MgO =Mg +O and the first-order interaction parameter,e _O ^Mg (e _Mg ^O ), were estimated to be logK _Mg = -7.8 ± 0.2 ande _O ^Mg = -190 ± 60 (e _Mg ^O = -290 ± 90), respectively. The activities of A1₂O₃ at the slag compositions double-saturated with CaO/MgO, MgO/ MgO A1₂O₃, and MgO Al₂O₃/CaO 2A1₂O₃ components were obtained from the S distribution ratios between slag and metal, coupled with the reported values of sulfide capacities. Nitride capacities were also estimated from the N distribution ratios and the activities of A1₂O₃.     

Study on Red Long-Time Luminescent Material Y2O2S:Eu,M (M = Mg,Ca, Sr,Ba)

The red long-time luminescent material Y₂O₂S:Eu³⁺, M (M = Mg, Ca, Sr, Ba) was prepared by high temperature solid-state method. The XRD result of the sample showed that the crystal phase was Y₂O₂S, which belong to hexagonal system, and no new crystal phase were by doping different amount of Mg, Ca, Sr, Ba. The excitation spectrum was a broad band within 200 × 400 nm region, the characteristic peaks of emission spectrum were located at 583, 595, 597, 617, 627, 707 nm. There was no marked change in excitation spectra, emission spectra and maximum of their wavelengths of the luminescent materials by doping with different ions. The luminescent intensity of the phosphors were stronger when the concentration of doping ions was Mg/Y = 6%, Ca/Y = 4%, Sr/Y = 8%, Ba/Y = 2.5%, respectively. Its sequence of luminescent intensity from high to low is Sr > Ba > Mg > Ca.     

Chemical equilibria between silicon and slag melts

The equilibria between silicon and slags of the systems CaO-SiO₂, Na₂O-SiO₂, and CaO-SiO₂-Y with Y being A1₂O₃, MgO, TiO_x, B₂O₃, and Na₂O have been investigated in silica crucibles. The calcium content under silica-saturated CaO-SiO₂ slag is 262 parts per million (ppm) at 1500 °C. The aluminum and magnesium contents increase with increasing alumina or magnesium oxide contents, respectively, reaching about 1800 ppm Al at silica/mullite or about 390 ppm Mg at silica/protoenstatite saturation. Boron has a distribution ratio [B]/(B₂O₃) of 0.18. The sodium content under silica-saturated Na₂O-SiO₂ slag is 25 ppm at 1500 °C. In contrast, the titanium content of the silicon, if Y is TiO_x, and (Ti) is in the percent range, is highand varies with the titanium content of the slag according to [wt Pct Ti] = 2.7 √(wt pctTi). In other experiments, it is shown that metallurgical grade (MG) silicon can be purified from aluminum, magnesium, and calcium by treatment with suitable silicate slags.     

Preparation of M2B5O9Cl:Eu2+(M=Sr,Ca) blue phosphors by a facile low-temperature self-reduction method and their enhanced luminescent properties

In this work,through a facile method of low-temperature(only 350 ℃) self-reduction,1D nano-sized M₂B₅O₉CI:Eu²⁺(M=Sr,Ca) blue phosphors with highly efficient performance can be obtained.The crystal structure,morphology and photoluminescence(PL) properties including thermal stability of M₂B₅O₉CI:Eu²⁺(M=Sr,Ca) phosphors were investigated.The M₂B₅O₉CI:Eu²⁺(M=Sr,Ca) phos...     

Thermodynamic Analysis of Deoxidation of Titanium Through the Formation of Rare-Earth Oxyfluorides

In this work, the possibility of the direct removal of oxygen species from metallic Ti through the formation of rare-earth oxyfluorides has been investigated from a thermodynamic viewpoint. The deoxidation limit of β-Ti using rare-earth metals (M: Y, La, Ce, and Nd) as deoxidants was evaluated. It was found that Ti metal with an oxygen concentration of 200 mass ppm or less could be theoretically obtained under the M/MOF/MF₃ equilibrium at 1300 K (1027 °C), which suggested a possibility of reducing the oxygen content in Ti below 500 mass ppm utilizing a fluoride-based molten salt. Furthermore, a new deoxidation process, in which oxygen was removed in the form of MOF compounds using Mg deoxidant, was discussed as well. The obtained results revealed that the oxygen content in β-Ti could be theoretically reduced to a level below 1000 mass ppm using a MF₃-containing molten salt equilibrated with Mg. Rare-earth metals and their alloys are usually produced by the electrolysis in a fluoride-based molten salt; hence, the modern industrial electrolysis techniques can be potentially utilized for deoxidizing Ti scrap.     

Evolution and deformability of inclusions in Al-killed steel with rare earth-alkali metals(Ca or Mg) combined treatment

The quality of stainless steel is closely related to the deformability of inclusions,which is significantly affected by their compositions.The present study first inve stigated the evolution of inclusion compositions in AI-killed steel with rare earth-alkali metals(Ca or Mg) combined treatme nt through four laboratory-scale experiments.The Ce contents in the final steel are 0.0080 wt%,0.015 wt%,0.016 wt% and 0.010 wt%,respectively.The Mg content is 0.0014 wt% in Ce-Mg combined treated steel,and ...     

Analysis of the complex deoxidation of carbon steel melts

The joint complex deoxidation of carbon steel melts is analyzed. A procedure is proposed to calculate the equilibrium oxygen concentration in a melt. Rail steel is used as an example to study the joint complex deoxidation of a melt by aluminum and silicon. Mullite (2Al₂O₃ · 3SiO₂) and kyanite (Al₂O₃ · SiO₂) are considered as the reaction products. Thermodynamic calculations demonstrate that the deoxidizing capacity of aluminum is increased in the presence of silicon in a melt. In this case, a substantial increase in the deoxidizing capacity in the concentration range 0.001–0.1 wt % Al is achieved when kyanite (Al₂O₃ · SiO₂) forms in the reaction products. The results of laboratory and industrial experiments on complex deoxidation are shown to agree well with the calculated data. These results demonstrate that the proposed calculation procedure can be recommended to determine the equilibrium oxygen concentration in a melt in the presence of several deoxidizing elements.     

On the Formation of non-metallic inclusions in fe-50 pct Ni type alloys by deoxidation with Mn,Si, and Al

This investigation deals with deoxidation experiments in 30 g lab melts of Fe-50 pct Ni alloys. After deoxidation with different amounts of Mn, Si and Al and their combinations the samples were quenched into water at different times. Metallographic studies comprising light microscopy, scanning electron microscopy, electron microprobe and image analysis were performed. Classical nucleation theory was used for computation of the different supersaturation with oxygen or the deoxidant necessary for homogeneous nucleation. The different deoxidation reactions and the transformation of inclusions due to diffusion of oxygen, or the deoxidant, from or into the inclusions was treated for the different cases of deoxidation. Most deoxidation reactions take place within some seconds. The experimental results were to be used to estimate the pertinent interfacial tensions between the oxides and the melt and the values obtained for the different oxides seemed to be reasonable. The diffusional computations were successfully used for predicting the different transformations taking place. For example, in deoxidation with 0.03 pct Si the oxygen solubility is controlled by the equilibrium with liquid FeO ⋅ SiO₂. The time taken to reach equilibrium is determined by the number of inclusions and the particle size. In deoxidation with 0.1 pct Si or more, the equilibrium is controlled by SiO₂ inclusions and the time taken to reach equilibrium, less than 1 s, is much shorter compared to the samples with 0.03 pct Si. The deoxidation reactions with aluminum were treated in the same way, and it was shown that the number of particles determined the time elapsing before equilibrium with respect to the formation of FeOAl₂O₃ or A1₂O₃. It was further shown that transformation of primary liquid FeOAl₂O₃ with high contents of FeO into solid FeOAl₂O₃ was expected to occur within one second. However, the experiments showed that it took somewhat longer, due to formation of solid FeOAl₂O₃ around the liquid FeOAl₂O₃ inclusions, thereby preventing the diffusion of aluminum into the particles.