The Thermodynamic Properties of Fe‐Mn‐C Melt at Reduced Pressure

The solubility of carbon in the Fe‐Mn‐C system was measured under reduced pressure of 1 Pa at 1573 K and 1673 K, respectively. The carbon solubility in terms of mole fraction in the iron based solution was found varying with manganese mole fraction in the solution and with temperature, as x_C= 0.1819 + 0.2531 x_Mn at 1573 K and x_C = 0.1981 + 0.2515x_Mn at 1673K. Manganese has a stronger influence on the carbon solubility at lower pressure than it has at higher pressure. The pressure was found to have an insignificant effect on the carbon solubility when manganese in the melt was absent. The activity interaction parameters between manganese and carbon in the alloy were determined from carbon solubilities at 1573 and 1673 K. Analysis of the experimental results showed that under vacuum conditions, the activity interaction parameter of manganese with carbon is higher than that at atmospheric pressure.     

Thermodynamic Behaviour of Chlorine in CaO‐SiO2‐MgO‐Al2O3(‐CaF2) Slags

The solubility of chlorine in CaO‐SiO₂‐Al₂O₃‐MgO(‐CaF₂) slag was measured at 1673 ‐1823 K. By estimating the chloride capacity of slags, thermodynamic behaviour of chlorine in the molten slag was investigated. Chloride capacity increased with increasing CaO / SiO₂ ratio (C/S). An increase in MgO content decreased chloride capacity at C/S≥1.0 because it lowered the activity of Ca²⁺ which seemed to have strong affinity with Cl^? in molten slag. Also, the chloride capacity decreased with increasing Al₂O₃ content. The affinity between the Ca²⁺ and Cl^? ions was confirmed by measuring the infrared spectra of slags. The dissolution reaction of chlorine into slag was exothermic and its molar enthalpy was evaluated from the experimental results at 1673 ‐ 1823 K. Based on the result obtained in the present study, the quantitative prediction of chlorine distribution during the blast furnace process was performed. It was estimated that almost all chlorine in the blast furnace would be absorbed into molten slag even if the PCI ratio was increased or low quality coal with chlorine content less than 1.0 mass% was injected.     

Influence of alumina and magnesia on phase equilibria in the system Fe‐CaO‐FeOn‐SiO2 at 1600 °C

The phase relations in the systems CaO‐FeO_n‐SiO₂‐Al₂O₃ and CaO‐FeO_n‐SiO₂‐MgO at 1600 °C saturated with liquid iron are described. The phase conditions in the quaternary system with aluminium oxide are so far rather unknown. An addition of aluminium oxide makes the calciumsilicates and lime saturation areas move towards the CaO corner thus enlarging the homogeneous liquidus space accordingly. Aluminium oxide can be considered as a flux in this case. The fields of different solid solutions in the system CaO‐FeO_n‐SiO₂‐MgO were taken into account. Some additional (2 to 4)‐phase areas occur with increasing MgO content. This causes the precipitation of magnesiowustite which dominates the system accordingly. The changed phase relations strongly influence the direction of tie‐lines and their length. Therewith, the correlation between liquid phase and solid phase, calculated via lever rule, is influenced, too.     

Thermodynamic properties of La2C3 and Gd2C3 at high temperatures

The enthalpies of lanthanum and gadolinium sesquicarbides were determined in the range 400–1900 K by the method of mixtures. The temperature dependences of the basic thermodynamic properties were calculated and tabulated. The temperatures, enthalpies, and entropies of the peritectic reactions were determined. Institute for Meterials Science Problems, Ukrainian Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 7–8, pp. 59–63, July–August, 1997.     

Nitrogen solubilities in CaO—CaF2 melts

Nitrogen solubilities in the CaO—CaF₂ system were determined under controlled oxygen partial pressures as well as at carbon saturation. Nitrogen contents (as N^3?) were shown to strongly depend on oxygen partial pressure from 10^?11 to 10^?13 atm. At carbon saturation both nitride and cyanide contents are also dependent on oxygen partial pressure, i.e. CO partial pressure. The dependence of nitride and cyanide contents on nitrogen partial pressure was found to be compatible with the theory and is described by the equations proposed in this paper. The results are also discussed in terms of nitride and cyanide capacities for a better understanding of the dissolution of nitrogen in slags of different composition. The temperature dependence of nitride content showed an increase in nitride content with increasing temperature.     

Thermodynamics of lead and bismuth in CaO–CaF2 melts

In order to understand a new refining process for removing tramp elements from alloy steels under strongly reducing conditions, the authors previously reported the thermodynamic behaviour of P, Sn, Sb, As and Cu in CaO–CaF₂ melts. In this investigation, the thermodynamic behaviour of Pb and Bi in CaO–CaF₂ melts under oxygen partial pressures from 10^?16 to 10^?20 atm was studied at temperatures ranging from 1360 to 1550°C, using a similar technique. It was shown that Pb and Bi exist in slag mainly as Ca₂Pb and Ca_1.5Bi, respectively, under very low oxygen partial pressure although a part of Pb is soluble in slags as metal. The obtained results were extrapolated to lower oxygen partial pressures to investigate the possibility of removing these tramp elements from molten iron, causing Bi to be removed from molten iron below an oxygen partial pressure of 10^?23 atm, whereas Pb is removed under higher oxygen partial pressures.     

Manganese Distribution between FeO‐MnO‐SiO2–CaO–MgO‐Al2O3 Slags and Molten Iron

Pretreatment of high manganese hot metal is suggested to produce hot metal suitable for further processing to steel in conventional LD converter and rich manganese slags satisfy the requirements for the production of silicomanganese alloys. Manganese distribution between slag and iron represents the efficiency of manganese oxidation from hot metal. The present study has been done to investigate the effect of temperature, slag basicity and composition of oxidizer mixture on the distribution coefficient of manganese between slag and iron. Ferrous oxide activity was determined in molten synthetic slag mixtures of FeO‐MnO‐SiO₂–CaO–MgO‐Al₂O₃. The investigated slags had chemical compositions similar to either oxidizer mixture or slags expected to result from the treatment of high manganese hot metal. The technique used to measure the ferrous oxide activity in the investigated slag systems was the well established one of gas‐slag‐metal equilibration in which molten slags contained in armco iron crucibles are exposed to a flowing gas mixture with a known oxygen potential until equilibrium has been attained. After equilibration, the final chemical analysis of the slags gave compositions having a particular ferrous oxide activity corresponding to the oxygen potential of the gas mixture. The determined values of ferrous oxide activity were used to calculate the equilibrium distribution of manganese between slag and iron. Higher manganese distribution between slag and iron was found to be obtained by using oxidizer containing high active iron oxide under acidic slag and relatively low temperature of about 1350°C.     

Thermodynamic behaviour of carbon in CaO-SiO2 slag system

In order to understand the thermodynamic behaviour of carbon in steelmaking slag at high temperature, the carbon dissolution into CaO-SiO₂ slag system has been investigated including the effects of temperature and slag components on the carbon dissolution reaction. It was found that carbide solubility in the CaO-SiO₂ slag decreased with increasing oxygen potential to confirm the theoretical relationship of ?1/2, which reflected the ionic exchange reaction mechanism between carbon and oxygen ions. Carbide solubility in slag as a function of slag basicity for various slag systems appeared to confirm this mechanism. This reaction mechanism implied that the carbide dissolution proceeded due to the reaction of solid carbon and oxygen ions supplied from (CaO) in slag. The oxygen ion appears to be the driving force as it is influenced by the slag components as well as the temperature as shown in the concept of the carbide capacity of slag. The solubility of carbide in the CaO-SiO₂ slag increased with the addition of CaF₂; the role of CaF₂ for carbide dissolution into slag could be speculated to have complex effects on indirect increase in basicity in spite of (CaO) dilution. Substitution of CaO by MgO decreased the solubility of carbide in the CaO-SiO₂-MgO slag, possibly caused by the relatively low electro-negativity of MgO.     

Thermodynamic behaviours of manganese and phosphorus between CaO‐MgOsat‐SiO2‐Al2O3‐FetO‐MnO‐P2O5 ladle slag and liquid iron

The thermodynamic equilibria of manganese and phosphorus between liquid iron and CaO‐MgO_Sat‐SiO₂‐Fe_tO‐MnO‐P₂O₅‐Al₂O₃ (0–33%) ladle slag have been investigated at 1873 K from the viewpoint of Mn and P yields for the production of high‐strength steels. The equilibrium distribution ratios of Mn and P were found to increase with increasing Fe_tO content; however, these ratios vary with basicity, but they do this the other way round. The addition of alumina into slag at a fixed basicity and Fe_tO content decreases both the equilibrium manganese and phosphorus distributions. The equilibrium distribution ratios were discussed in terms of the variation of activity coefficients of Fe_tO, MnO and PO_2.5, according to the slag basicity and Al₂O₃ content. The quantitative contributions of basicity and (%Fe_tO + %MnO) on L_Mn and L_P were empirically determined and their usefulness was discussed with the aid of plant data: To improve Mn and P yields in the practical RH operation, it is strongly recommended that Fe‐Mn and Fe‐P alloys be added after Al deoxidation treatment inducing relatively high Al₂O₃ in slag and maintaining low Fe_tO content. In addition, a ladle slag composition for the targeted Mn and P contents in liquid iron was substantially estimated using the empirical relationships.     

The solubility of water vapour in CaO‐SiO2‐Al2O3‐MgO slag system

The solubility of water vapour in the CaO‐SiO₂‐Al₂O₃‐MgO quaternary slag system was measured using an inert gas fusion technique with thermal conductivity detection. The slags were equilibrated with argon‐water vapour mixture corresponding to 0.157 bar of water vapour pressure at 1873 K. The slag solubility of water vapour is proportional to the square root of vapour pressure. Since the hydroxyl capacity of slag, C_OH shows an independence on the relative amount of CaO or MgO in slag, the contributions of CaO and MgO on the hydroxyl capacity are equivalent on a molar basis. Whereas, Al₂O₃ shows a better effect on the hydroxyl capacity than SiO₂. A linear relationship between hydroxyl capacity and slag basicity in logarithmic scale was obtained with the slope of 1/2, confirming the water vapour dissolution reaction into a basic slag as (O^2‐) + H₂O(g) = 2(OH^?). The correlation between hydroxyl capacity and slag components was derived in terms of their contributing weight factors. The measured values of C^'_OH agree well with the calculated ones using the interaction energies of α_H‐Al = ?38300 and α_H‐Mg = ?22700 J determined with the aid of the regular solution model. In addition, the correlation between hydroxyl capacity and sulphide capacity was empirically derived as a formula of logC_OH = 1/2logC_S + (4.38 ± 0.25) through the thermodynamic expression of both capacities by virtue of the common oxygen ion activity.     

Thermodynamics of antimony,arsenic, and tin in CaO—CaF2 melts

In view of the importance of tramp element contamination of steel products through a large volume of scrap consumption in the near future, the thermodynamic behaviour of Sb, As, Sn and Cu in CaO—CaF₂ melts under reducing conditions was studied by examining the dependences of distribution of each element between Cu, Ag or Sn alloys and CaO—CaF₂ melts on the CaO activity, oxygen partial pressure and temperature around 1 500°C. As a result, the reaction products on treatment by Ca compounds were demonstrated to be Ca₃Sb₂, Ca₃As₂, Ca₂Sn and CaCu. Experimentally obtained distributions were extrapolated to lower oxygen partial pressures less than 10^?18 atm to estimate the feasibility of removing those tramp elements from molten iron. It is thermodynamically indicated that if the prevailing oxygen partial pressure of the environment is below 10^?23 atm, these impurities, except Cu, would be substantially removed from molten steel.     

Thermodynamic properties of lanthanum silicides at high temperatures

The enthalpies of five lanthanum silicides were determined over the temperature range 380–2225 K by the method of mixtures. Values of the basic thermodynamic functions of the materials were calculated and tabulated, as well as the temperatures, enthalpies, and entropies of fusion. The temperatures and enthalpies of fusion were related to the relative concentrations of silicon in the compounds.Institute of Materials Science Problems, Ukrainian National Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 3–4, pp. 48–53, April–May, 1994.     

The oxygen pressure of dilute FexO‐CaO‐Al2O3 slag in equilibrium with liquid iron

The relationship between slag composition and oxygen partial pressure of dilute Fe_xO‐CaO‐Al₂O₃ slag in equilibrium with iron the activity of which is below 1 was extrapolated to give the oxygen partial pressure of a slag equilibrated with iron of the activity 1. In the process of extrapolation, the oxygen partial pressure and the activity of iron were unified to give a single thermodynamic quantity which is defined as: , where K(x) is the equilibrium constant for the formation reaction of Fe_xO and is considered to be a function of x. The dependence of on the slag composition was obtained experimentally. On the other hand, it was found that the plot of against log a_Fe has the slope ?1 as expected from the theoretical consideration. The relation has been employed to estimate the composition of slag in equilibrium with liquid iron. Thus, the obtained composition is used to calculate the values of and of the slag in equilibrium with liquid iron.     

萤石对改善高炉高铝渣性能的影响

高炉生产实践表明,炉渣w（Al2O3）超过16%会对炉况稳定顺行产生较大影响,甚至引起高炉失常。在w（Al2O3）为17%、18%、19%、20%、21%的炉渣中添加0%、2%、4%、6%、8%、10%的w（CaF2）,测定了炉渣黏度的变化。研究表明,炉渣中w（Al2O3）在17%～18%,起降低黏度作用的w（CaF2）最低为2%。最后介绍了某高炉加萤石处理炉况失常的情况。     

Thermodynamic behaviour of carbonate in CaO based slag

Carbonate solubility was measured for CaO bearing slag systems at 1600 °C under different thermodynamic conditions by using equilibration techniques. Carbonate solubility increased with activity of (CaO). The reaction mechanism of the carbonate dissolution in slag can be expressed as a reaction between CO₂ gaseous phase and oxygen ion to form carbonate (CO₃^2-). Carbonate capacities of various slags depended not only on oxygen ion but also activity coefficient of carbonate ion. The activity coefficient of carbonate ion in CaO-SiO₂ slag changed with CaO content, but that of CaO-Al₂O₃ slag did not change remarkably. Substitution of MgO by CaO for solubility of carbonate had a similar effect as in the case of carbide in CaO-SiO₂-MgO slag. The critical oxygen potential for carbide and carbonate stability was found to be 10-¹⁰ bar.     

Thermodynamic Activities of “FeO” in some Binary “FeO”‐Containing Slags

In the present investigation, experimental measurements of the thermodynamic activities of iron oxide in the Al₂O₃‐“FeO”, CaO‐“FeO” and “FeO”‐SiO₂ systems were performed in the temperature range 1823‐1873 K by using gas equilibration technique. The molten slag, kept in a Pt‐crucible was brought to equilibrium with a gas mixture of known oxygen partial pressure. A part of the Fe from the “FeO” was reduced during the equilibration and got dissolved in the Pt phase. The samples were quenched after the required equilibration time and the slag phase as well as the platinum crucible was subjected to chemical analysis. The activities of “FeO” in the slag were calculated from the experimental data using thermodynamic information on the Fe‐Pt binary metallic system generated and assessed earlier. The experimental results are compared with earlier thermodynamic studies of the slag systems. Reassessment with the KTH slag model is performed and the results are compared with other thermodynamic models, viz. F*A*C*T? and Thermo‐Calc? respectively. The experimental activities predicted by the KTH slag model are in good agreement with the experimental data available in the literature. A general agreement between the various models is also observed.     

Oxidation State of Titanium in CaO‐SiO2‐TiOx Slags at 1873K

Oxidation state of titanium was determined in CaO‐SiO₂‐TiO_x slags in the composition range 25‐53 percent CaO, 27‐46 percent SiO₂, 10‐55 percent TiO_x at 1873K using gas equilibration method. In the experiments, slags with different titanium oxide contents were equilibrated with a known carbon monoxide and carbon dioxide ratio. The results were used to determine the Ti³⁺ and Ti⁴⁺ contents as well as the activity coefficient ratio of corresponding oxides in the slag. The dependence of the activity coefficient ratio as a function of oxygen partial pressure was determined.