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Steelmaking slag is considered as a promising phosphorus resource as it contains the phosphorus in a condensed phase of Ca2SiO4–Ca3P2O8 solid solution (C2S–C3P)ss. In the present study, the carbothermic reduction of (C2S–40 mol% C3P)ss at 1573 K was carried out to understand the phosphorus removal mechanism by varying reduction temperature, external gas flow rate, amount of graphite, and concentration of Ca3P2O8 in (C2S–C3P)ss. The carbothermic reduction proceeded as a zero-order reaction when the temperature was 1573 K, despite the P2O5 concentration decrease with the reduction time. At temperatures less than 1473 K, the reduction did not occur. Based on the XRD analysis of the reduced (C2S–C3P)ss samples, it was found that carbothermic reduction of the C2S–C3P solid solution proceeded by the decomposition of the C2S–C3P solid solution into CaO and C2S with the removal of phosphorus, but not by a uniform decrease of the phosphorous throughout the C2S–C3P solid solution. The overall reduction degrees were found to be independent of the reduction rate (zero-order reaction) and the P2O5 concentration in the (C2S–C3P)ss. From these independencies, the rate-controlling step of the carbothermic reduction of (C2S–C3P)ss was concluded to be the Boudouard reaction.

The crystallography of the Ca2SiO4-Ca3P2O8 solid solutions in the dephosphorization slag in current steelmaking process was determined in this study. Understanding the physical and chemical properties of these Ca2SiO4-Ca3P2O8 solid solutions is a preliminary step towards understanding the role of the Ca2SiO4-Ca3P2O8 solid solutions in the dephosphorization process. The range of Ca3P2O8 in the Ca2SiO4-Ca3P2O8 solid solutions synthesized for analysis varied from 10 to 90 mol pct, with an incremental increase of 10 mol pct per solid solution. In solid solutions with a Ca3P2O8 content of up to 40 mol pct, the crystal structure at 1773 K was found to be hexagonal, while the solid solutions with a Ca3P2O8 content over 70 mol pct had a trigonal structure. The silicocarnotite solid solutions observed when the Ca3P2O8 content was 50 to 60 mol pct were likely formed by phase transformation during cooling. In the stable solid solution with a Ca3P2O8 content of 50 to 60 mol pct at 1773 K before the occurrence of transformation, the crystal structure is trigonal since it is in the Ca3P2O8-rich range. A linear increase in the lattice parameters c of the solid solutions in the range of (0, 40 mol pct) and (70 mol pct, 100 mol pct) was found with increasing Ca3P2O8 content. The lattice parameter a, however, was almost independent of the Ca3P2O8 content in the solid solutions.

To design optimal pyrometallurgical processes for nickel and cobalt recycling, and more particularly for the end-of-life process of Ni–Co–Fe-based end-of-life (EoL) superalloys, knowledge of their activity coefficients in slags is essential. In this study, the activity coefficients of NiO and CoO in CaO–Al2O3–SiO2 slag, a candidate slag used for the EoL superalloy remelting process, were measured using gas/slag/metal equilibrium experiments. These activity coefficients were then used to consider the recycling efficiency of nickel and cobalt by remelting EoL superalloys using CaO–Al2O3–SiO2 slag. The activity coefficients of NiO and CoO in CaO–Al2O3–SiO2 slag both show a positive deviation from Raoult’s law, with values that vary from 1 to 5 depending on the change in basicity. The activity coefficients of NiO and CoO peak in the slag with a composition near B = (%CaO)/(%SiO2) = 1, where B is the basicity. We observed that controlling the slag composition at approximately B = 1 effectively reduces the cobalt and nickel oxidation losses and promotes the oxidation removal of iron during the remelting process of EoL superalloys.

In ironmaking, maintaining gas permeability in blast furnace with low coke rate operation is essential to reduce carbon emissions. The high pressure loss in the cohesive zone decreases the gas permeability and affects the productivity of blast furnace. In order to increase the gas permeability in the cohesive zone, the thickness of the cohesive layer should be decreased. For this purpose, increasing softening temperature and decreasing dripping temperature of the iron ore are desired. In this study, softening, melting, and permeation of SiO2-FeO-CaO-Al2O3-MgO on a coke bed were investigated. The oxide sample in a tablet form was heated under CO/CO2 atmosphere, and the shape of the tablet was observed. The softening and melting temperatures of the SiO2-FeO-CaO system changed with the addition of Al2O3 and MgO. Oxide tablets with and without Al2O3 softened below and above the solidus temperature, respectively. The melting temperatures varied with the ratio of CO/CO2 in the gas. The permeation temperature was independent of the melting temperature, but dependent on the wettability.

The recoverability of phosphorus oxide from steelmaking slag was investigated using a mechanical approach involving capillary action. It was found that P2O5 was concentrated in the 2CaO·SiO2 phase. To separate the P2O5-enriched solid 2CaO·SiO2 phase and FeO-rich liquid phase in steelmaking slag, capillary action was used to facilitate penetration into absorbers such as sintered CaO, Fe2O3, and CaCO3 tablet. Once the liquid phase had penetrated the absorber, it was found that the solid 2CaO·SiO2 phase and FeO-rich phase could be effectively separated. When CaCO3 was used as an absorber, 91 % of phosphorus oxide in the steelmaking slag was recovered in solid 2CaO·SiO2 phase. The recovered absorber, which includes a FeO-rich liquid phase, may be used as Fe source, and the 2CaO·SiO2 phase, which includes P2O5, may be used as P source.

Suppression of CO2 discharged from iron- and steel- making companies is an example of the biggest issues for the protection of global environment and sustainable growth of steelmaking industry. One of the efforts made to decrease the emission of CO2 in ironmaking process is blowing of hydrogen gas into blast furnace. Hydrogen gas can reduce iron oxide and form harmless H2O. Cementite (Fe3C) may be formed by introduction of hydrogen into blast furnace and play an important role on carburization and smelting behavior of reduced iron. The conditions that Fe3C was formed were experimentally determined by changing CO–CO2–H2 gas composition in the present work. As the result, it was found that there is a possibility of Fe3C formation by hydrogen gas introduction into blast furnace. Therefore, the effect of Fe3C on smelting behavior of reduced iron was also observed, and it was confirmed that the presence of Fe3C will have positive effect on enhancing carburization and smelting of reduced iron.

The Ti deoxidation equilibrium of Fe–Ni, Fe–Cr and Fe–Cr–Ni alloys saturated with ‘Ti3O5’ and Ti2O3 phase was clarified in previous researches. Solubility of Fe, Cr and/or Ni oxides in ‘Ti3O5’ phase equilibrated with liquid Fe–Ni, Fe–Cr and Fe–Cr–Ni alloys at 1823 K to 1923 K were measured by SEM–EDS. It was confirmed that the solubility of Fe, Cr and/or Ni oxide in ‘Ti3O5’ phase at low Ti content increase with decrease of Ti content in alloys. Titanium content that dissolution of Fe, Cr and/or Ni oxide into ‘Ti3O5’ phase becomes apparent increases with increase of Cr and/or Ni content of the alloys. The activity of Ti deoxidation product, ‘Ti3O5’ phase, equilibrated with Fe–Ni, Fe–Cr and Fe–Cr–Ni alloys was also evaluated by Redlich-Kister type polynomial. Equilibrium between Ti and O at low Ti content of those alloys was analyzed using the activity of ‘Ti3O5’ phase.

Elution of fluorine from landfill slag by rainwater or groundwater causes serious problems; hence, fixation of fluorine in electric arc furnace reducing slag (EAFRS) is crucial. The phase including fluorine was identified for some EAFRS specimens and confirmed is as (3CaO·2SiO2)·CaF2 in the current work. Experiments to determine the dissolution of fluorine from the EAFRS into water were conducted at pH 4, 7, and 10. It was found that fluorine tended to elute under acidic conditions. Therefore, the elution of fluorine from fluorine-containing substances into water at pH 4 was investigated in detail. It was found that 2(2CaO·SiO2)·CaF2, (3CaO·2SiO2)·CaF2, and CaF2 were unstable, while the 3(3CaO·P2O5)·CaF2 phase was stable; further, fluorine elution from 3(3CaO·P2O5)·CaF2 into water was found to be limited. On the basis of these results, it was concluded that the dissolution of fluorine into water can be suppressed by adding a sufficient amount of P2O5 to EAFRS, so that the formation of unstable fluorine-containing substances is prevented.

The most important subject in the steelmaking process is the control of non-metallic inclusions. Non-metallic inclusions with a high melting point do not deform during a hot working process because they are relatively hard. Hence, the inclusion composition should be controlled in order to achieve a low melting point to prevent product defects. Therefore, an MnO–SiO2-based inclusion is considered to be one of the preferred systems. Moreover, the heat treatment of austenitic stainless steel has been reported to influence the composition of MnO–SiO2-type inclusions; these inclusions change into MnO–Cr2O3-type, MnO–Nb2O5-type, and MnO–V2O3-type inclusions. In this study, we investigated the influence of heat treatment on the composition of the inclusions in the martensitic stainless steel. In general, a scanning electron microscope–energy dispersive x-ray spectrometer (SEM–EDS) is used for the quantitative analysis of inclusions; however, SEM–EDS cannot simultaneously analyze a large number of inclusions. Therefore, a new technique using the SEM–EDS along with the image analysis software “Particle Analysis” was used for the chemical analysis and the size measurement of a large number of inclusions (hereafter abbreviated as the PA method). The heat-treatment-induced compositional change of the inclusions in martensitic stainless steel was evaluated by using both the analysis methods.

Utilization of steelmaking slag is indispensable for sustainable growth of steelmaking industry. Steelmaking slag contains nutrition such as phosphorus, silicon and iron and may be utilized as a fertilizer if elution of environmentally regulated elements is negligible. Chromium is contained in stainless steel slag as an oxide and stabilization of this chromium oxide in the slag is very important in the view of environmental protection.Elution behavior of elements from chromium containing phases into seawater was investigated to observe the stability of phases that may exist in steelmaking slag. It was found that the existence of 2CaO·SiO2 enhanced the dissolution of chromium into seawater. Elution behavior of chromium from especially synthesized stainless steel slag into seawater was investigated. Finally, fixation of chromium was conducted by control of mineralogical phase with SiO2 addition to stainless steel slag. Addition of SiO2 to the slag was very effective for prevention of chromium elution into seawater.

Suppression of CO2 discharged from iron and steelmaking companies is an example of the biggest issues for the protection of global environment and sustainable growth of steelmaking industry. One of the efforts made to decrease the emission of CO2 in ironmaking process is blowing of hydrogen gas into blast furnace. Hydrogen gas can reduce iron oxide and form harmless H2O. Cementite (Fe3C) may be formed by introduction of hydrogen into blast furnace and play an important role on carburization and smelting behavior of reduced iron. In the present work, Fe3C sample was held at 800–1 100 K under Ar atmosphere to clarify the stability and the behavior of Fe3C phase. It was confirmed that metastable Fe3C phase will decompose under Ar atmosphere at 800 K and rapidly decompose at temperature over 900 K. Also, it was found that composite of nano-size C and Fe will form when Fe3C decompose.

Currently, several metals are commercially recycled from by-products and wastes by metallurgical processing. However, the metallurgical process has each characteristic, which causes limitation for resource recovery. The combinations of elements in secondary resources, such as by-products and wastes, are often different from those in natural resources. There are even combinations that are not present in natural resources. Conventional metallurgical processes have been optimized for economical and efficient extraction of desired elements only from large amount of ores under constant grade. Therefore, in order to extract metals from secondary resources by the conventional metallurgical process, it is necessary to estimate the recoverability of the constituent elements by taking into account their chemical properties well in advance. In particular, analysis for combination of elements is significantly important. In this study, we developed the evaluation method of metal resources recoverability based on thermodynamic analysis, and made clear the element distribution among gas, slag and metal phases during metal recovery based on thermodynamic analysis. In an application of the method shows that Cu, and precious metals (Ag, Au, Pt, Pd) present in mobile phones can be recovered as metals in the pyrometallurgy process of Cu in a converter. Other elements distributed in the slag phase are difficult to recover. The result of our analysis reflects the trends observed in the distribution of metals in copper metallurgy, thereby indicating the validity of our proposed evaluation method.

Currently, several metals are commercially recycled from by-products and wastes by metallurgical processing. However, the metallurgical process has each characteristic, which causes limitation for resource recovery. The combinations of elements in secondary resources, such as by-products and wastes, are often different from those in natural resources. There are even combinations that are not present in natural resources. Conventional metallurgical processes have been optimized for economical and efficient extraction of desired elements only from large amount of ores under constant grade. Therefore, in order to extract metals from secondary resources by the conventional metallurgical process, it is necessary to estimate the recoverability of the constituent elements by taking into account their chemical properties well in advance. In particular, analysis for combination of elements is significantly important. In this study, we developed the evaluation method of metal resources recyclability based on thermodynamic analysis, and made clear the element distribution among gas, slag and metal phases during metal recovery based on thermodynamic analysis. In an application of the method shows that Cu, and precious metals (Ag, Au, Pt, Pd) present in mobile phones can be recovered as metals in the pyrometallurgy process of Cu in a converter, while Pb and Zn can be recovered as vapor. Other elements distributed in the slag phase are difficult to recover. The result of our analysis reflects the trends observed in the distribution of metals in copper metallurgy, thereby indicating the validity of our proposed evaluation method.

Equilibrium relation between Ti and O in molten Fe–Ni alloy has been investigated at 1873 to 1923 K. Ti oxide equilibrated with molten Fe–Ni alloy has been determined by EBSD (Electron Backscatter Diffraction) pattern analysis using FE-SEM (Field Emission Scanning Electron Microscope). The present results have been numerically analyzed by the excess Gibbs free energy change of mixing for the Fe–Ni–Ti–O system with Redlich–Kister type polynomial. Redlich–Kister type polynomial parameters concerning Ni and Ti were determined as follows,0ΩNi–Ti = 424280−270.40T J/mol (XTi

Titanium deoxidation equilibria between Ti and O in molten Fe–Cr and Fe–Cr–Ni alloys were investigated at temperatures of 1823 to 1923 K. Titanium oxides equilibrated with molten Fe–Cr and Fe–Cr–Ni alloys have been determined by EBSD (Electron Backscatter Diffraction) pattern analysis using FE-SEM (Field Emission Scanning Electron Microscope). Deoxidation product changes from Ti2O3 to Ti3O5 with decrease of Ti content in Fe–Cr and Fe–Cr–Ni alloys.Binary interaction parameters of Redlich–Kister type polynomial between Cr and O was assessed by using the previous experimental result in the Fe–Cr–O system. Experimental result of titanium deoxidation in molten Fe–Cr alloy has been numerically analyzed by the excess Gibbs free energy change of mixing Fe–Cr–Ti–O system with Redlich–Kister type polynomial. Validity of evaluated parameters between Cr–O (ΩCr–O) and Cr–Ti (ΩCr–Ti) was confirmed by comparison with experimental result for Fe–Cr–Ni alloy.Binary interaction parameters of Redlich–Kister type polynomial in present work were evaluated as follows,0ΩCr–O = −52870−24.10T J/mol (XO

Iron nugget making process by rapid heating reduction of powdery iron ore and pulverized coal mixture is regarded as one of the novel iron-making processes. Iron carburization during smelting reduction is especially important reaction step from the viewpoint of saving energy in this process. If the rate and efficiency of carburization reaction are increased, energy consumption of the process will be reduced to large extent. The purpose of this study is to clarify the carburization degree of iron nugget during smelting reduction of the mixture.The sample was prepared from graphite, electrolytic iron powder and synthetic slag containing iron oxide to simulate iron carburization phenomena during smelting reduction of the mixture in the present work. The sample was quenched immediately after the mixture changed into nugget shape in a rapid heating process. Laser microscope combined with infrared image furnace was used for sample heating and observation of carburization phenomena, and carbon content in the nugget was chemically analyzed after quenching.From above-mentioned investigations, it was revealed that the occurrence of carburization during smelting reduction in the sample mixture is advantageous to obtain higher carbon contain iron nugget.

Magnesium deoxidation equilibrium of molten Fe–Cr–Ni alloy was determined by a chemical equilibrium method at temperature of 1873 to 1973 K. Extreme care was taken of oxygen analysis of the samples. Numerical analysis on Mg deoxidation of molten Fe–Cr–Ni alloy has been carried out by utilizing the model based on Darken's quadratic formalism and Redlich-Kister type polynomial. Magnesium deoxidation equilibrium can be expressed in wide composition region of the Fe–Cr–Ni alloy.

The effect of temperature on oxygen activity in steel was studied in plant trials where temperature and oxygen activity were measured at two depths and at the same time during different parts of la ...

The equilibrium relation between Ti and O in liquid Fe has been measured only at 1 873 K on the condition of various kinds of titanium oxides saturation in our previous paper. The present work deals with the equilibrium between Ti and O in liquid Fe saturated with 'Ti 3 O 5 ' and Ti 2 O 3 at 1 823 K and 1 923 K for full understanding temperature dependence. Also, equilibrium phase changes of titanium oxides with various Ti contents in molten Fe have been identified as the equilibrium titanium oxides with electron backscatter diffraction (EBSD) pattern analysis technique. The present results have been thermodynamically evaluated combining with previous results on the various thermodynamic values as a function of temperature. The equilibrium constants and the interaction parameters of Wagner's formalism were given as a function of temperature in the present work as follows. Ti 2 O 3 (s) = 2Ti + 3O [-10.61, 0.28

Aluminum deoxidation equilibrium of molten Fe–Ni alloy was determined by chemical equilibrium method at temperature of 1873 to 1973 K. Also, critical point in molten Fe–40mass%Ni alloy that coexisted with Al2O3 and FeO·Al2O3 was determined experimentally at 1973 K. Solvent extraction method was applied to improve the analytical accuracy of the low aluminum content in molten Fe–Ni alloy. The relation between aluminum and oxygen contents in molten Fe–Ni alloy equilibrated with Al2O3 or FeO·Al2O3 was estimated in the whole alloy composition range at 1873 to 1973 K by utilizing the metallic solution model based on Darken's quadratic formalism and Redlich–Kister type polynomial.

To investigate the slag permeation to packed bed of carbonaceous materials, the measurement of molten slag's densities, surface tensions and dynamic contact angle on carbonaceous materials at relatively low temperatures (from 1 673 to 1 773 K) are carried out by applying the sessile droplet method. The interfacial compositions of slags and carbonaceous materials were examined by SEM/EDX. SiC at carbonaceous material surface was not observed. The variation of measured density, contact angle and surface tension with time were found to be almost negligible with given slag composition and at given temperature. It is reported that carbonaceous material wettability at the temperature of more than 1 873 K was strongly dependent on the slag composition as well as carbon properties. The almost constant contact angel with time in this study can be attributed to the negligible formation of SiC at carbonaceous material surface. The slag permeation model has been developed along with the measurement of physical properties. The maximum retention height of liquid layer on the sphere packing layer is expressed by H c =A/L c +L c /2, where A is constant and H c and L c are the dimensionless slag layer retention height and the dimensionless sphere's diameter, respectively. Slag layer retention height on the carbonaceous material packing layer is evaluated using the measured physical properties. The proposed characteristic length λ(=√ -γL cosθ/pg) in the model can be used to characterize the slag permeation behaviour.

The equilibrium between Ti and Q has been investigated in molten Fe-Ti alloy saturated with various kinds of titanium oxides at 1 873 K. The present results have been thermodynamically analyzed applying Wagner's formalism as well as Darken's quadratic formalism with the excess Gibbs free energy change of mixing described by Redlich-Kister type polynomial. The equilibrium constants and the interaction parameters of Wagner's formalism were given as follows at 1 873 K in the present work. Ti 2 O 3 (s)=2Ti+3O (0.5

There are huge quantities of uncertainties on the Ti deoxdiation equilibrium constants and their interaction parameters in the literatures including the recommended values by the Japan Society for the Promotion of Science (JSPS). The main reason of such uncertainties among the previous works is due to the insufficient information of titanium oxide phase in equilibrium with liquid Fe–Ti alloy. The measurement of the equilibrium phase changes of titanium oxides with various Ti contents in molten Fe–Ti alloy has been carried out in the present study. Molten Fe–Ti alloys with various Ti contents have been equilibrated with ‘Ti3O5’ crucibles at 1 873 K. The kinds of Ti oxide at the interface of ‘Ti3O5’ crucible contacted with molten Fe–Ti alloys have been identified as the equilibrium titanium oxides with the electron backscatter diffraction (EBSD) pattern analysis technique. After the ‘Ti3O5’ crucible reacted with molten Fe–Ti alloys adequately and both of them were quenched.The present result on the stable region of equilibrium titanium oxides with Ti contents in Fe–Ti alloy was in good agreement with the thermodynamically calculated results based on the free energies of titanium oxides formation and the activity of Ti in Fe–Ti alloy.

Numerical analysis on Si deoxidation of molten Fe, Ni, Fe-Ni, Fe-Cr, Fe-Cr-Ni, Ni-Cu and Ni-Co alloys have been carried out. The excess Gibbs free energy change of mixing has described with Redlich-Kister type polynomial using the relation derived from Darken's quadratic formalism. Excellent agreement between present work and experimental results was found for equilibrium Si and O contents in molten Fe, Ni, Fe-Ni, Fe-Cr, Fe-Cr-Ni, Ni-Cu and Ni-Co alloys. Si deoxidation equilibrium of not only one component metal but also alloys can be analyzed numerically using the formula determined in the present work. Also, interaction parameters of Redlich-Kister type polynomial can be easily converted into interaction coefficients with Taylor's series, which are widely used in steelmaking processes.

The most serious issues in the world are a large amount of energy consumption and generation of greenhouse effect gas from iron-making industry. The main factors of energy consumption are reduction of iron ore and carburization of reduced iron at high temperature. If it is possible to accelerate the rates of iron ore smelting reduction and the succeeding carburization at low temperature, the technology will be very valuable to lower energy consumption in the blast furnace. It is well known that phenomena during smelting reduction are very complicated and the mechanism has not yet been clarified. Therefore, "in-situ" observation of smelting reduction and carburization of iron sample were carried out in our previous work. It was confirmed from the results that iron was carburized without a direct contact with carbonaceous material during smelting reduction. The mechanisms of this unique carburization were discussed and it was obtained a conclusion that formation rate of Fe-C particles caused by smelting reduction mainly determined the overall rate of iron carburization reaction.

Suppression of CO 2 and waste such as slags discharged from iron- and steelmaking processes are some of the typical biggest issues for the protection of global environment and sustainable growth of steelmaking industry. Utilization of active phytoplankton growth will be one of the best options to stabilize and suppress carbon dioxide at high-efficiency. Inorganic minerals such as C, O, N, Si, P and Fe are necessary for phytoplankton multiplication. It is crucial for supply of nutrition into seawater effectively for phytoplankton multiplication to understand the dissolution behavior of some elements from steelmaking slags into seawater. Firstly, the morphology of the precipitated phases in steelmaking slags during cooling period was investigated in the present work. Secondary, the dissolution behavior of some elements from steelmaking slags and pure substances such as 4CaO . P 2 O 5 (8.5mass% P), 3CaO . P 2 O 5 (10.0 mass% P) and 2CaO . SiO 2 -3CaO . P 2 O 5 (2.8mass% P) solid solution phase into artificial seawater has also been studied. Thirdly, the dissolution mechanism of elements from steelmaking slags was discussed by using stability diagrams of Si, P and Fe in seawater.

Steelmaking slag contains nutrition such as Si, P and Fe for acceleration of phytoplankton growth. Phytoplankton can fixate carbon dioxide more than any other creatures on the earth. Hence, suppression of CO 2 can be achieved by educing the potential of steelmaking slag as the nutrition for their propagation. When it is considered to supply nutrition from steelmaking slag to seawater, we must avoid hazardous elements dissolution from steelmaking slag into seawater. In the present work, the dissolution behavior of Ca, Mg, Mn and F from steelmaking slags into artificial seawater was studied continuously with our previous paper. The dissolution mechanism of elements from steelmaking slags was discussed again by using stability diagram in seawater.

Steelmaking slag contains nutrition such as Si, P and Fe and it is reported by our group that dissolved Si, P, Fe can accelerate phytoplankton growth by photosynthesis. Phytoplankton can fixate more carbon dioxide at unit earth surface area than any other creature on this planet. This means that by educing the potential of steelmaking slag, suppression of CO 2 in the atmosphere and utilization of steelmaking slag can be achieved. In consideration of nutrition supply from steelmaking slag to seawater, we must avoid hazardous element dissolution from steelmaking slag into seawater. The elution mechanism of fluorine into the artificial seawater has been studied based on dissolution behavior of fluorine from synthesized fluorine containing substances into artificial seawater in the present work.

Relation between the activity coefficient expressed by Darken's quadratic formalism and the excess Gibbs energy change of mixing described with Redlich-Kister type polynomial was discussed on Si deoxidation of Fe-Ni and Ni-Co alloys. The activity coefficients of Si and O in metal expressed by quadratic formalism have been converted into formula using interaction parameters Ω i - j under the condition where concentration of Si and O are dilute. Numerical analysis on Si deoxidation of molten Fe-Ni and Ni-Co alloy has been carried out. It has been found to be outstanding in the agreement of equilibrium Si and O contents in molten Fe-Ni and Ni-Co alloy analyzed in the present work with the experimental results. The deoxidation equilibrium of not only one component metal but also alloy can be analyzed numerically using the formula determined in the present work.

Relation between the activity coefficient expressed by Darken's quadratic formalism and the excess Gibbs energy change of mixing described by Redlich-Kister type polynomial was discussed in Si deoxidation of Ni alloy. The activity coefficients of Si and O in metal expressed by quadratic formalism have been converted into formula using interaction parameters Ω i-j under the condition where concentration of Si and O are dilute. Numerical analysis on Si deoxidation of molten Ni and Ni-Cu alloy has been carried out. It has been found to be outstanding in the agreement of equilibrium Si and O contents in molten Ni and Ni-Cu alloy analyzed in the present work with the experimental results. The deoxidation equilibrium of not only pure metal but also alloy can be analyzed numerically using the formula determined in the present work.