Thermodynamics of the oxygen solutions in aluminum-containing Fe-Co melts

Thermodynamic analysis of aluminum-containing Fe-Co melts is performed. The equilibrium constants of the deoxidation of iron-cobalt melts with aluminum, the activity coefficients during infinite dilution, and the interaction parameters in melts with various compositions are determined. The oxygen solubility in the melts under study is studied as a function of the cobalt and aluminum contents. Aluminum is characterized by a very high affinity to oxygen in iron-cobalt melts. The deoxidizing capacity of aluminum substantially increases with the cobalt content in the melt. The curves of the oxygen solubility in aluminum-containing iron-cobalt melts have a minimum, whose position shifts to lower aluminum contents as the cobalt content in the melt increases. Further aluminum additions increase the oxygen concentration in the melt: the higher the cobalt content in the melt, the sharper the increase in the oxygen concentration after the minimum when aluminum is added to the melt. The aluminum contents at the minimum points in the oxygen solubility curves are determined, and the corresponding minimum oxygen concentrations are found.     

Thermodynamics of the oxygen solutions in manganese-containing Fe-Co melts

Thermodynamic analysis of the oxygen solutions in manganese-containing Fe-Co melts has been performed. The equilibrium constants of deoxidation reaction of iron-cobalt melts with manganese, the activity coefficients during infinity dilution, and the interaction parameters in various melts are found. During the deoxidation of manganese-containing Fe-Co melts, the oxide phase contains FeO and CoO along with MnO. The compositions of the oxide phase above Fe-Co-Mn-O melts are calculated. When the cobalt and manganese contents in the melts increase, the mole fraction of manganese oxide increases, and it approaches 1 in the case of pure cobalt. The dependences of the oxygen solubility in the melts on the cobalt and manganese contents are calculated. The deoxidizing capacity of manganese increases substantially with increasing cobalt content in the melt. The curves of oxygen solubility in Fe-Co melts have minima, whose values shift toward low manganese content in a melt. The manganese contents are determined at the minimum points in the oxygen solubility curves, and the corresponding minimum oxygen contents are found.     

Interaction of silicon-containing melts with single-crystal aluminum oxide

The sessile droplet method is used to study the wettability of aluminum oxide (single-crystal Al₂O₃, i.e. sapphire) by melts of Au-Si, Cu-Si, Ni-Si, Pd-Si, and Ge-Si in relation to silicon concentration, temperature and exposure time. Addition of silicon to melt leads to a fall in the wetting angle from 120–140° for Au, Cu, Ni, Pd and Ge to 70–90° for an alloy with 30–70 at.% Si. The adhesion activity of silicon (a nontransition element) is lower than for transition metals (for example, Ti, Zr). In the systems Au-Si and Pd-Si a phenomenon of dewetting (the wetting angle increases after the initial spreading) is observed. Interphase chemical processes responsible for the wetting angle are studies by mass spectrometry, microscope and profilographic analyses for metal alloys and the surface of solid sapphire.     

Thermodynamics of oxygen solutions in the complex reduction of Fe-Co melts

Thermodynamic analysis of the complex reduction of metal melts is considered. The proposed analytical method identifies the influence of the weaker reducing agent in amplifying the effect of the stronger reagent. The curves of oxygen solubility pass through a minimum. Analysis of the extremal curves of oxygen concentration in the melt as a function of the content of reducing agents yields a formula for the content of the stronger reducing agent such that the oxygen concentration is minimal. Thermodynamic analysis of the combined influence of aluminum and silicon on the oxygen solubility in Fe-Co melts indicates that the reaction products may contain both mullite (3Al₂O₃ · 2SiO₂) and kyanite (Al₂O₃ · SiO₂). The presence of silicon in the melt intensifies the reducing action of aluminum: slightly when mullite is formed and significantly when kyanite is formed. When kyanite is formed, the curves of oxygen solubility pass through a minimum, whose position depends on the aluminum content in the melt but not on the silicon content. The aluminum content at the minimum declines slightly from iron to cobalt, as for Fe-Co-Al systems. Further addition of aluminum elevates the oxygen concentration. The formation of the compounds Al₂O₃, 3Al₂O₃ · 2SiO₂, Al₂O₃ · SiO₂, and SiO₂ is investigated as a function of the Al and Si content in the melt.     

The apparent solubility of aluminum in cryolite melts

The apparent solubility of aluminum in cryolite melts saturated with A1₂O₃ has been determined by titration with electrolytically generated O₂. The results may be expressed by wt pct Al = − 0.2877 + 0.0268 (NaF/AlF₃ wt ratio) + 2.992 × 10⁻⁴ (temp °C) − 0.00192 (% CaF₂) −0.00174 (% Li₃AlF₆) −0.00288 (% NaCl) with a standard deviation of ±0.017. Ranges covered were ratio 0.8 to 2.3, temperatures 969° to 1054°C, CaF₂ ≤ 14 pct, Li₃AlF₆ ≤ 20 pct, and NaCl ≤ 10 pct. There was no significant effect of adding 0 to 38. pct K₃A1F₆ or 0 to 10 pct MgF₂. It was found that solubility was approximately proportional to activity of aluminum when Al-Cu alloys were used. Possible mechanisms of solution are discussed. Monovalent aluminum is ruled out on the basis of the variation of solubility with NaF/AlF₃ ratio and a_Al. The favored, but not proven, mechanism involves formation of both sodium atoms and a colloidal dispersion of aluminum.     

The equilibrium solubility of nitrogen in aluminosilicate melts

The equilibrium solubility of nitrogen in aluminosilicate melts, similar in composition to many blast furnace slags, has been measured, although the silica contents under investigation have been limited by experimental problems to between 30 and 38 mole pct. The solubility is a chemical rather than a physical phenomenon, it being necessary to impose severe reducing conditions to obtain significant quantities of nitrogen in solution. The dependence of solubility on slag basicity has been investigated, and a simple dependence upon nitrogen and carbon monoxide contents in the gas phase established. From the results, it is postulated that an exchange reaction takes place between nitrogen gas and bridging oxygen atoms in the aluminosilicate structure, and the results are discussed in relation to the structure of the melts.     

Nitrogen solubility in CaO-CaF2-SiO2 melts

The preceding paper^[5] demonstrated that nitrogen dissolves in silicate melts either as a free ion or complex anion, being incorporated into silicate networks. In the present study, the influence of CaF₂ addition to CaO-SiO₂ melts on the nitrogen solubility was investigated along the liquidus at 1573 K and within the liquidus at 1723 K at constant CaF₂ levels. In the latter case, as the SiO₂ content increases from CaO saturation, the total nitrogen content decreases to reach the minimum and then starts to increase up to the SiO₂ saturation. This is in accord with the abovementioned mechanism of nitrogen dissolution, which is supported by the changing behavior of free and incorporated nitrogen contents with the slag composition. The role of CaF₂ is complicated through the formation of fluorosilicates. The CaF₂ seems not to function simply as a diluent but to enhance the dissolution of nitrogen by releasing oxygen from silicate networks, promoting the formation of free nitride ions. Formerly Graduate Student, Department of Metallurgy, The University of Tokyo.     

On the solubility of aluminum in cryolitic melts

The solubility of aluminum in NaF-AlF₃-Al₂O₃ melts with various additives was found to increase with increasing NaF/AlF₃ molar ratio (CR) and increasing temperature and to decrease with additions of A1₂O₃, CaF₂, MgF₂, and LiF to the melts. With the use of literature data for the activities of NaF and A1F₃ in cryolitic melts, three dissolution reaction models were found to give a good fit to the experimental solubility data. According to the most probable of these models the total concentration of dissolved aluminum (aluminum and sodium species) is given by c_Al = c_Na(diss) + c_AlF2- + c_Al2F3- + c_Al3F4- + c_Al4F5- In NaF rich melts, aluminum will dominantly dissolve as sodium, while at cryolite ratios commonly used in aluminum electrowinning (CR = 2.25 to 2.7) the AlF _-2 ^- -ion is the predominant dissolved metal species. Other species (A1₂F₃ ^-, A1₃F₄-, A1₄F₅-) were found to be of some significance only in melts with high excess A1F₃ (CR < 2).     

On the solubility of aluminum in cryolitic melts

The solubility of aluminum in NaF-AlF₃-Al₂O₃ melts with various additives was found to increase with increasing NaF/AlF₃ molar ratio (CR) and increasing temperature and to decrease with additions of A1₂O₃, CaF₂, MgF₂, and LiF to the melts. With the use of literature data for the activities of NaF and A1F₃ in cryolitic melts, three dissolution reaction models were found to give a good fit to the experimental solubility data. According to the most probable of these models the total concentration of dissolved aluminum (aluminum and sodium species) is given by c_Al = c_Na(diss) + c_AlF2- + c_Al2F3- + c_Al3F4- + c_Al4F5- In NaF rich melts, aluminum will dominantly dissolve as sodium, while at cryolite ratios commonly used in aluminum electrowinning (CR = 2.25 to 2.7) the AlF _-2 ^- -ion is the predominant dissolved metal species. Other species (A1₂F₃ ^-, A1₃F₄-, A1₄F₅-) were found to be of some significance only in melts with high excess A1F₃ (CR < 2).     

Carbon solubility as carbide in calcium silicate melts

R.A. Berryman, Formerly Graduate Student, Department of Metallurgy and Materials Science, University of Toronto,     

On the solubility of aluminum carbide in cryolitic melts

The solubility of aluminum carbide in cryolitic melts was determined as a function of NaF/A1F₃ molar ratio (CR), temperature, and the concentrations of A1₂O₃, CaF₂, MgF₂, and LiF. At 1020 °C a maximum concentration of 2.1 wt pct aluminum carbide was found at CR = 1.80. The following model for the aluminum carbide dissolution reaction based on activity data for NaF and A1F₃ was found to fit the experimental solubility data: Al₄C₃(s) + 5AlF₃(diss) + 9NaF(l) = 3Na₃Al₃CF₈(diss). From the solubility data for aluminum carbide an empirical equation giving the equilibrium carbide concentration was derived for CR > 1.80.     

Oxygen and sulfur solubilities in Ni-Fe-S-O melts

Oxygen and sulfur solubilities were determined in Ni-Fe-S-O melts under the following conditions: 10^-11.50 ≤ P_O2 ≤ 10^-8.50 atm; 10^-3.00 ≤ P_{s 2} ≤ 10^-2.00 atm; 0.19 ≤ Ni/(Ni + Fe) ≤0.85; and 1473 K ≤T ≤ 1573 K. The oxygen solubility was found to increase with increasing partial pressure of oxygen up to a maximum value at oxide saturation and to decrease with increasing equilibrium partial pressure of sulfur. The ferrous metal content enhanced oxygen solubility. The trends in dissolution behavior of sulfur were opposite to those of oxygen with respect to changing P_{O 2} and P_{S 2} and to the Ni/(Ni + Fe) ratio; however, at high matte grades Ni/(Ni + Fe) > approximately 0.5, sulfur solubility appeared to decrease as a function of the Ni/(Ni + Fe) ratio, as did oxygen solubility. The standard Gibbs energy of oxygen dissolution in Ni-Fe-S-O melts Ni/(Ni + Fe) = 0.47 in the temperature range 1473 to 1573 K can be described by ΔG° = −202.5 + 0.0660 T(K) (±1.5 kJ/mol)     

On the solubility of aluminum carbide in cryolitic melts

The solubility of aluminum carbide in cryolitic melts was determined as a function of NaF/A1F₃ molar ratio (CR), temperature, and the concentrations of A1₂O₃, CaF₂, MgF₂, and LiF. At 1020 °C a maximum concentration of 2.1 wt pct aluminum carbide was found at CR = 1.80. The following model for the aluminum carbide dissolution reaction based on activity data for NaF and A1F₃ was found to fit the experimental solubility data: Al₄C₃(s) + 5AlF₃(diss) + 9NaF(l) = 3Na₃Al₃CF₈(diss). From the solubility data for aluminum carbide an empirical equation giving the equilibrium carbide concentration was derived for CR > 1.80.     

The prediction of the nitrogen solubility in binary iron melts

Statistical model of nitrogen solubility in iron melts. Equations. Calculation of nitrogen solubility of the systems Fe–Co–N, Fe–Cr–N, Fe–Mn–N and Fe–Ni–N in the liquid state at 0.101 MPa. Comparison between model and experiments.     

Oxygen activities in Cr-containing Fe and Ni-based melts

Plug-type, ZrO₂-based oxygen sensors have been used for long-term measurements of oxygen activity in Fe–O–Cr and Ni–O–Cr melts. In these melts, equilibrated with chromium oxide, oxygen activities a_O were determined as a function of Cr content. From the experimental results, data were derived for activity coefficients f_O and of 1st and 2nd order interaction parameters e_O^Cr and r_O^Cr. Cr₂O₃ has been identified as the oxide phase in equilibrium with the metal melt at ≥ 5 wt.% Cr in the case of iron and at ≥ 0.2 wt.% Cr in the case of nickel. Oxygen activities and oxygen contents in Cr-containing iron melts are lowered with increasing additions of nickel. Further investigations were directed to a_O determination in Fe–O–Cr–C and Fe–O–Cr–Al melts.