Solubility of carbon in CaO-B2O3 and BaO-B2O3 slags

The solubility of carbon in molten CaO-B₂O₃ and BaO-B₂O₃ slags at high temperatures was measured to understand the dissolution mechanism of carbon into the slags. The B₂O₃-bearing slags, which have a wide range of liquids, at the temperature of interest have been applied to investigate the effect of basicity on the solubility of carbon from the saturation of acidic or basic components. The solubility of carbon, as a function of the composition of slags, shows a minimum value, and it is suggested that carbon dissolves by different mechanisms in the acidic and basic slags, respectively. From the infrared spectra measurements, the wave number indicating the B-C bond was found to be about 1150 cm⁻¹ in the acidic region of slags; hence, the incorporation of carbon into the borate network was confirmed qualitatively. The carbide capacity was compared to the nitride capacity, showing that the dissolutions of carbon and nitrogen into the slags are similar.     

Quantitative analysis of the relative basicity of CaO and BaO by silver solubility in slags

The solubility of silver in molten CaO-B₂O₃ and BaO-B₂O₃ slags at high temperatures was measured to seek a new measure of the basicity of slags. The B₂O₃-bearing fluxes, which have wide range of liquids at the temperature of interest, have been applied to investigate the effects of flux composition on the solubility of silver from the saturation of acidic or basic components. The solubility of silver in slags has a minimum value as a function of flux composition, and it is suggested that silver behaves as an amphoteric substance and dissolves by different mechanisms in acidic and basic fluxes. The solubility of silver decreased with the increasing temperature and content of basic oxides in the acidic region, and vice versa in the highly basic region. In the acidic region, BaO is more basic than CaO by, at most, about 33 pct, based on the difference of the solubility of silver in both slags, indicating that BaO is not a much-stronger basic oxide than CaO in the acidic slags. In the highly basic region, BaO is about 5 times more basic than CaO. The solubility of silver in slags was compared to the nitride capacity, showing that the dissolutions of silver and nitrogen into the melts are similar to each other. The relationship between Ag solubility and theoretical optical basicity was also discussed.     

Thermodynamic study on the effect of CaF2 on the nitrogen and carbon solubility in the CaO-Al2O3-CaF2 slag system

The nitrogen and carbon solubilities in the CaO-Al₂O₃-CaF₂ slag system at 1723K were measured to understand the effect of CaF₂ on the nitrogen and carbon dissolution behaviour using thermochemical equilibration technique. The nitride capacity in the CaO_satd.-Al₂O₃-CaF₂ system was constant until X_Al2O₃ / X_CaF2 = 0.23, followed by decrease with an increase in X_Al2O₃ / X_CaF2 ratio, and then showed a constant value. The carbide capacity in the CaO_satd.-Al₂O₃-CaF₂ system also showed the similar behaviour to the nitride capacity, however, the effect of CaF₂ on the activity coefficient of nitride and carbide ions showed some differences in case of X_CaF2 = 0.2. The effect of CaF₂ on the activity coefficient of carbide and nitride ions would not be significant in case of CaO-rich region of X_CaO / X_CaF2 = 0.31. However, CaF₂ could be expected to affect the activity coefficient of each ion in case of the Al₂O₃-rich region, causing compensating effect of the incorporated nitride (carbide) mechanism. The relationship between nitride and carbide capacity was also discussed.     

The Thermodynamic Behavior of Copper in the CaO-B<Subscript>2</Subscript>O<Subscript>3</Subscript> and BaO-B<Subscript>2</Subscript>O<Subscript>3</Subscript> Slag System

The Cu solubility was measured in the CaO-B₂O₃ and BaO-B₂O₃ slag systems to understand the dissolution mechanism of Cu in the slags. The Cu solubility had a linear relationship with oxygen partial pressure in the CaO-B₂O₃ slag system, which corresponds with previous studies. Also, the Cu solubilities in slag decreased with increasing the slag basicity, which value of slope was close to –0.5 in logarithmic form. From the results of experiment, the Cu dissolution mechanism established as follows:

Removal of nitrogen from steel using novel fluxes

The solubility of nitrogen and the nitride capacity of CaO-Al₂O₃-TiO₂ and CaO-BaO-Al₂O₃-TiO₂ slags were measured at 1873 K using a gas-slag-metal equilibration technique with carbon-saturated iron and gas mixtures of CO and N₂. The nitride capacity increased with increasing the TiO₂ and BaO content and is significantly higher than the nitride capacity for normal ladle slags. The activity coefficient of TiO₂ in CaO-Al₂O₃-TiO₂ and CaO-BaO-Al₂O₂-TiO₂ systems were measured. This is necessary to know in order to estimate the possible pickup of titanium in the metal when an aluminum-killed steel is treated with these slags. Also, the activity coefficient of Ti in carbon-saturated iron was measured. The kinetics of the nitrogen reaction between slag and metal is influenced by the oxygen potential in the metal and is primarily controlled by liquid-phase mass transfer of nitrogen in the metal. Formerly with the Department of Metallurgical Engineering and Materials Science, Carnegie Mellon University     

Phase equilibrium data and liquidus for the system “MnO”-CaO-(Al2O3 + SiO2) at Al2O3/SiO2 = 0.41

Phase-equilibrium data and the liquidus for the system “MnO”-CaO-(Al₂O₃-SiO₂) at a manganese-rich alloy saturation have been determined in the temperature range from 1423 to 1723 K. The results are presented in the form of a pseudoternary section “MnO”-CaO-(Al₂O₃ + SiO₂) with an Al₂O₃/SiO₂ weight ratio of 0.41. The following primary phases are present in the range of conditions investigated: 3Al₂O₃·2SiO₂; SiO₂; MnO·Al₂O₃·2SiO₂; (Mn,Ca)O·SiO₂; 2(Mn,Ca)O·SiO₂; MnO·Al₂O₃; (Mn,Ca)O; α-2CaO·SiO₂; α′-2CaO·SiO₂; 2CaO·Al₂O₃·SiO₂; CaO·SiO₂, and CaO·Al₂O₃·2SiO₂. The presence of alumina in this system is shown to have a significant effect on the liquidus compared to the system “MnO”-CaO-SiO₂, leading to the stabilization of the anorthite and gehlenite phases.     

Thermodynamic behavior of Na2O-B2O3 melt

The activity of Na₂O in a Na₂O-B₂O₃ melt was measured at 1373 K by a chemical equilibration technique to understand the thermodynamic behavior of this slag system. Also, the activity coefficient of Na in Ag was preliminarily measured as fundamental thermodynamic data, to estimate the activity of Na₂O in the slag. Sodium in the silver melt, within the present concentration range, exhibits the Henrian behavior, and the Henrian activity coefficient of Na in Ag (γ ⁰ _Na) is estimated to be 37.5 at 1373 K, indicating a positive deviation from ideality. The activity of Na₂O in the slag varies from 1.86×10⁻⁶ to 4.99×10⁻⁴ when its content is increased from 11.0 to 64.9 mol pct; this indicates a significant negative deviation from ideality. The excess stability does not exhibit any pronounced peak, despite being drastically changed at specific slag compositions. Comparing the molar Gibbs free energy of mixing in various binary slags, Na₂O was considered to be more basic than BaO (CaO) was, followed next by MgO; also, P₂O₅ would be significantly more acidic than SiO₂ would be, followed next by B₂O₃. Comparing the heats of formation of solid compounds in binary slags, the larger the differences in the electronegativity values between slag components, the more the relative ionic characters of the melts seemed to be.     

Solubility of nitrogen and carbon in CaO-Al2O3 melts in the presence of graphite

CaO-Al₂O₃ slags were melted in graphite crucibles under N₂–CO–Ar gas mixtures at 1600°C. The contents of total nitrogen, cyanide and total carbon of the slags were determined by chemical analyses of quenched samples taken by suction from the melt. The nitrogen is present in the melt as nitride N⁻³ ion and cyanide CN⁻¹ ion, and carbon as cyanide and carbide C ₂ ²⁻ ion. The equilibrium constants for the respective reactions were evaluated. It is found that the nitride capacity of the melt decreases whereas the cyanide and carbide capacities increase with increasing CaO/Al₂O₃ ratio.     

A study of the sulfide capacities of iron-oxide containing slags

Sulfide capacities of iron-oxide containing slags in the “FeO”-Al₂O₃-SiO₂, “FeO”-CaO-SiO₂, “FeO”-MgO-SiO₂, and “FeO”-MnO-SiO₂ systems were experimentally determined using gas-slag equilibration technique. The experiments were conducted in a temperature range of 1673 to 1923 K. The experimental data were employed to optimize the model parameters of a sulfide capacity model developed earlier in the present laboratory. Based on these parameters, along with those obtained in previous works, an equation was suggested to predict the sulfide capacities of the “FeO”-Al₂O₃-CaO-MgO-MnO-SiO₂ slags. The results of model predictions show reasonable agreement with the experimental values of the six-component slags determined as a part of this work.     

Solubility of nitrogen in CaO-SiO2-CaF2 slag system

Equilibrium experiments between gas and slag were carried out to understand the thermodynamic behaviour of nitrogen in the CaO-SiO₂-CaF₂ slag system at 1600°C. The solubility of nitrogen in this slag system increased as the oxygen potential decreased and as the reaction temperature increased. The values of the nitride capacity have a minimum at about 2.0 slag basicity, having higher values in both more acidic and basic regions. This may be explained by two mechanisms for nitrogen dissolution; incorporated nitride ion and free nitride ion state. In slag with 2.0 basicity or less, MgO content increased the nitride capacity slightly. At higher slag basicity, however, nitride capacity decreased with MgO content. The effects of BaO to substitute CaO on nitride capacity showed similar behaviour as MgO. This complex relationship between basicity of slag and nitride capacity is explained by using optical basicity. It was found that nitride capacity and optical basicity had a close relationship even in the different basic oxide systems.     

Thermodynamics of nitrogen in CaO-SiO2-AI2O3 slags and its reaction with Fe-Csat. melts

The solubility of nitrogen as the nitride ion in CaO-SiO₂-Al₂O₃ slags in equilibrium with N₂-CO gas mixtures and carbon was measured at 1823 K. The nitride capacity (C _N3-) was calculated to compare the nitrogen contents measured under different nitrogen and oxygen potentials.C _N3- decreased with increasing basicity and by replacing SiO₂ with A1₂O₃. The nitrogen partition ratio between carbon saturated iron and the slag was measured in CO gas at one atmosphere at 1823 K. By comparing the partition ratios with the corresponding nitride capacities measured by the gas-slag experiments, it was concluded that the oxygen partial pressure at the slag-metal interface was controlled by the Fe-FeO reaction. A new definition of nitride capacity was proposed based on the reaction between nitrogen and the network former,i.e., SiO₂ or A1₂O₃. This capacity could consistently explain the experimental results. Empirical equations were derived to estimate the activity coefficients of silicon and aluminum nitrides in the slags. On leave of absence from the Research Institute of Mineral Dressing and Metallurgy, Tohoku University, Sendai, Japan.     

A study of nitrogen solubility in Na2O‐B2O3 slag

The nitrogen solubility and nitride capacity of a Na₂O‐B₂O₃ slag system were investigated in a concentration range of Na₂O mass contents up to 40 % at 1373K. The solubility of nitrogen in Na₂O‐B₂O₃ slag was found to be proportional to the oxygen partial pressure to the power of ?3/4, and it was also found to increase with increasing reaction temperature. The nitride capacity of the slag decreased with increasing Na₂O content. From the experimental results it was concluded that nitrogen dissolution into Na₂O‐B₂O₃ slags (Na₂O mass contents < 40 %) occurs by its reaction with both free oxygen ions and with oxygen ions incorporated with the network.     

Activity Calculation Model for Ternary Slag System of Al2O3-BaO-B2O3

According to the ion and molecule coexistence theory, the activity model of Al₂O₃-BaO-B₂O₃ ternary slag system was established, and the influences of BaO/Al₂O₃ molar ratio, B₂O₃ mole fraction and temperature on the activity of the slag system were investigated. Finally, the equal activity curves were drawn with the model results. The results show that with the increase of BaO/Al₂O₃ ratio, the activity of Al₂O₃ is significantly reduced, the activity of BaO ? Al₂O₃ is increased obviously, and the activity of 2Al₂O₃ ? B₂O₃ is also decreased. With the increase of B₂O₃ mole fraction, the activity of BaO ? Al₂O₃ decreased significantly, while the activities of BaO ? 2B₂O₃ and 2Al₂O₃ ? B₂O₃ increased. In addition, the influence of temperature on the activities of different components is comparatively smaller than the influence of BaO/Al₂O₃ ratio and B₂O₃ mole fraction.     

Phosphate capacity of CaO-AI2O3 slags containing CaF2, BaO,Li2O,or Na2O

Phosphorus partition ratios between CaO-Al₂O₃ and CaO-Al₂O₃-CaF₂ fluxes and Fe-C_sat-P alloys have been measured as a function of slag composition at 1500 °C. The effects of additions of BaO, Li₂O, and Na₂O to the CaO-Al₂O₃-CaF₂ system on the phosphorus partition ratios at 1400 °C and 1300 °C have been measured. From the partition ratio, and assuming that the oxygen potential is controlled by C-CO equilibrium, the phosphate capacities of the fluxes were calculated. Also, the activities of Li₂O and Na₂O were measured as a function of slag composition at 1300 °C by equilibrating the flux and the metal with Pb-Li or Pb-Na alloy and CO in a graphite crucible. The results indicate that phosphorus partition ratios with carbon-saturated iron and the phosphate capacities for additions of more basic oxides decrease in the following order: Na₂Oτ;Li₂Oτ;BaO. The activities of Li₂O and Na₂O in calcium aluminate fluxes have large negative deviations from ideal behavior; the activity coefficients at infinite dilution are on the order of 0.05 and 10^-5, respectively. Formerly Graduate Student, Department of Metallurgical Engineering and Materials Science, Carnegie Mellon University     

Solubility of BaS in BaO-BaF2 slag and the Influence of FeOx,SiO2, Cr2O3, BaCI2, CaO,and MgO on the sulfide capacity of this system

The influence of SiO₂, FeO_x, Cr₂O₃, BaCl₂, CaO, and MgO on the sulfide capacity of the BaO-BaF₂ system was measured at 1473 K, using a gas-slag-metal equilibration technique. It was found that the substitution of BaF₂ by SiO₂, FeO_x, Cr₂O₃, and BaCl₂ decreases the sulfide capacity of the BaO-BaF₂ system. Similar results were obtained for the carbonate capacity. The CaO-saturated BaO-BaF₂ flux, however, was found to have slightly higher sulfide and carbonate capacities than the pure BaO-BaF₂ flux. The solubility of CaO increased with increasing BaF₂ content and was 18 mol pet in BaF₂ at 1473 K. The solubility of MgO in the BaO-BaF₂ system at the same temperature is very low, and it has no effect on the sulfide and carbonate capacities. The solubility of BaS in the BaO-BaF₂ system was also measured at 1473 K and had its maximum for the slag containing 40 mass pet BaO. The activity of BaO in the system was calculated from those data. IVAN P. RACHEV, formerly Graduate Student, Department of Metallurgy, The University of Tokyo.     

Determination of the standard gibbs energy for the reaction of 3BaO (s) + 2Cr (s) + 3/2O2 (g) = 3Ba0 · Cr2O3 (s)

The standard Gibbs energy of formation of 3BaO · Cr₂O₃ has been measured by a chemical equilibrium technique and is expressed as follows: 3BaO (s) + 2Cr (s) + 3/2 O₂ (g) = 3BaO · Cr₂O₃ (s) ΔG^o = -1,260,000 (±3000) + 282 (±24)r(J/mol) The activity coefficient of chromium in copper, which was needed for the foregoing measurement, may be expressed by the following equation: 5790 log γ _Cr ^{o =5790/T-2.10} The value of standard Gibbs energy at 1573 K was found to be close to that of reaction of formation of CaO · Cr₂O₃ expressed in the similar form. The BaO saturated BaF₂ flux is shown to be far more promising in the oxidative dephosphorization of chromium-containing hot metal in comparison with the CaO-SiO₂-CaF₂ flux doubly saturated with CaO and 3CaO-Cr₂O₃.     

Liquidus temperatures in calcium ferrite slags in equilibrium with molten copper

Experimental laboratory methods have been developed that enable phase-equilibria studies to be carried out on slags in the system Ca-Cu-Fe-O in equilibrium with metallic copper. These techniques involve equilibration at temperature, rapid quenching, and chemical analysis of the phases using electron-probe X-ray microanalysis (EPMA). Equilibration experiments have been carried out in the temperature range of 1150 °C to 1250 °C (1423 to 1523 K) and in the composition range of 4 to 80 wt pct “Cu₂O,” 0 to 25 wt pct CaO, and 20 to 75 wt pct “Fe₂O₃” in equilibrium with metallic copper. Liquidus and solidus data are reported for the primary-phase fields of spinel (magnetite) and dicalcium ferrite. The resulting data have been used to construct liquidus isotherms of the CaO-“Cu₂O”-“Fe₂O₃” system at metallic copper saturation.     

Phase equilibrium studies in the “MnO”-Al2O3-SiO2 system

Phase relations and the liquidus surface in the system “MnO”-Al₂O₃-SiO₂ at manganese-rich alloy saturation have been investigated in the temperature range from 1373 to 1773 K. This system contains the primary-phase fields of tridymite and cristobalite (SiO₂); mullite (3Al₂O₃·2SiO₂); corundum (Al₂O₃); galaxite (MnO·Al₂O₃); manganosite (MnO); tephroite (2MnO·SiO₂); rhodonite (MnO·SiO₂); spessartine (3MnO·Al₂O₃·SiO₂); and the compound MnO·Al₂O₃·2SiO₂.     

Solubility of nitrogen and carbon in CaO-Al2O3 melts in the presence of graphite

CaO-Al₂O₃ slags were melted in graphite crucibles under N₂-CO-Ar gas mixtures at 1600°C. The contents of total nitrogen, cyanide and total carbon of the slags were determined by chemical analyses of quenched samples taken by suction from the melt. The nitrogen is present in the melt as nitride N^3- ion and cyanide CN^-1 ion, and carbon as cyanide and carbide C_2- ion. The equilibrium constants for the respective reactions were evaluated. It is found that the nitride capacity of the melt decreases whereas the cyanide and carbide capacities increase with increasing CaO/Al₂O₃ ratio.