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.     

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 solubility in silicon-containing Fe-Co melts

Thermodynamic analysis of the oxygen solutions in silicon-containing Fe-Co melts is performed. The equilibrium constant of silicon deoxidation of iron-cobalt melts, the activity coefficients for infinite dilution, and the interaction parameters for melts differing in composition are determined. The dependences of the oxygen solubility in the melts under study are calculated for different cobalt and silicon contents. The deoxidizing capacity of silicon increases substantially as the cobalt content in a melt increases. The curves of oxygen solubility in Fe-Co melts have a minimum; the minimum oxygen solubility shifts to a low silicon content as the cobalt content in the melts increases. The silicon contents for the minima in the curves of oxygen solubility and the minimum oxygen concentrations corresponding to the silicon contents are determined.     

A model for silicate melts

Formerly Research Fellow of the Royal Institute of Technology     

Solubilities of carbon dioxide in sodium silicate melts

Carbonate solubilities in Na₂O-SiO₂ melts were measured over the composition range X_{Na 2}O/ (X_{Na 2}O + X_{SiO 2}) = 0.5 to 1.0 and the temperature range 1100 to 1300 ‡C. The solubility increased with increasing X_Na2_O and decreased with increasing temperature. Carbonate capacities calculated from the experimental results compared favorably with values for sulfide and phosphate capacities obtained from the literature. In addition, an excellent correlation was obtained between carbonate capacity and the activity of sodium oxide. The carbonate capacity, which is an easier parameter to obtain, is a good measure of the basicity of sodium silicate melts. It would appear that carbonate capacity could be an excellent basicity index for iron and steelmaking slags as well as for fluxes used in other high temperature technologies. Formerly with University of Toronto. Formerly with the Department of Metallurgy, University of Tokyo.     

The thermodynamic activity of ZnO in silicate melts

The activity of ZnO in ZnO-SiO₂ and CaO-ZnO-SiO₂ melts has been measured at 1560 °C using a transpiration technique with CO-CO₂ mixtures as the carrier gas. The activities of ZnO in dilute solution in 42 wt pct SiO₂?38 wt pct CaO-20 wt pct A1₂O₃ in the range 1400° to 1550 °C and in 62 wt pct SiO₂?23.3 wt pct CaO?14.7 wt pct A1₂O₃ at 1550 °C have also been measured. The measured free energies of formation of ZnO-SiO₂ melts are significantly more negative than published estimated values and this, together with the behavior observed in the system CaO-Al₂O₃-SiO₂, indicate that ZnO is a relatively basic oxide. The results are discussed in terms of the polymerization model of binary silicate melts and ideal silicate mixing in ternary silicate melts. The behavior of ZnO in dilute solution in CaO-Al₂O₃-SiO₂ melts is discussed in terms of the possibility of the fluxing of ZnO by iron blast furnace slags.     

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.     

Modeling of sulfide capacities of silicate melts

An examination of the solution chemistry of sulfides in silicates leads to a method for the calculation of the sulfide capacities of silicate melts using the Flory model for polymeric silica chains. Calculations for the CaO−SiO₂, FeO−SiO₂, and MgO−SiO₂ binary systems at 1773 K and 1923 K are shown to be in good agreement with available experimental data and to be more reliable than calculations based on the empirical concept of basicity.     

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).     

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).     

Magnesium-thermic synthesis of molybdenum carbide in ion melts

The physicochemical aspects of the synthesis of the powders of molybdenum carbide by the magnesium-thermic reduction of its oxide in melts of lithium, sodium, and potassium carbonates are considered. The thermodynamic evaluation of reactions based on the synthesis is given. The influence of the melt temperature on the granulometric characteristics of the carbides is revealed. It is shown that the powders with the largest specific surface are formed in the melt of lithium carbonate (Mo₂C of 7.96 m²/g) at 750°C.     

Fuming of stannous oxide from silicate melts

The kinetics of vaporization of SnO from silicate melts was studied in helium, nitrogen, argon and argon-helium mixtures, and in inert gas—carbon monoxide mixtures. The rate of extraction of tin from the meltvia SnO vaporization was significantly higher in reducing gases than in inert gases. The enhanced vaporization phenomenon, commonly recognized in metallic systems, is demonstrated to occur in silicate melts. The vapor phase reduction of SnO (g) was studied experimentally, and the reduction was found to be very rapid. The addition of acidic or basic oxides to the binary SnO-SiO₂ melts decreased the vaporization rate.     

Densities and molar volumes of silicate melts

Abstract

Expressions are derived for densities and molar volumes of binary and ternary silicate melts based on the interpretation that the constitution of the melts can be described in tern-IS of conventional polymer theory. For simplicity, the treatment is limited to the case in which only linear chains are considered to be present. The assumptions in this approach are that (a) the value of k_ln for the equilibrium constant of the polymerization process, as expressed in terms of the activities of the constituents, is independent of the chain length n of the reacting species, and (b) the enthalpy change for the mixing of the pure constituents is identical with the change in internal energy. It is readily shown that these are equivalent to the assumptions that there is a constant increment in standard free energy of formation and molar volume on passing from one member to the next along the homologous series of pure liquid silicates and that, for the molar volumes, this increment is equal to that on passing from the oxide to the pure liquid orthosilicate. Densities and molar volumes calculated on this basis are in good agreement with experiment for basic melts in the systems FeO-SiO₂, PbOSiO₂, FeO-CaO-SiO₂, FeO-MnO-SiO₂ and FeO-CoO-SiO₂. The treatment becomes inexact near the metasilicate composition due to the neglect of cyclic and network structures, not allowed in the theory. The increment in molar volume due to the MSiO₃ group, as calculated from the data, varies between 40 and 50 cm³ and increases with the ionic radius of the cation.

Résumé

Des expressions ont été dérivées pour calculer les densités et les volumes molaires des silicates binaires et ternaires fondus en supposant que la composition des silicates peut être représentée par la théorie conventionnelle de polymères. Pour cette analyse nous utilisons simplement Ie formalisme de chîines linéaires avec les hypothéses que: (a) la valeur de k_ln, la constante d'équilibre du procédé de polymérisation reliant les activités des constituants, est indépendante de la longueur de chaîne “n” des réactifs et (b) que l'enthalpie de mélange des composants purs est identique à l'énergie interne de mélange. On peut démontrer que ces hypothéses reviennent à supposer qu'il existe un acroissement constant dans l'enthalpie libre standard de formation et dans le volume molaire au cours de la progression entre les séries homologues de silicates purs fondus. Pour les volumes molaires, cet accroissenlent correspond à la différence entre l'oxyde et l'orthosilicate pur liquide. Sur cette base les valeurs calculées des densités et des volurnes molaires se comparent bien avec les valeurs expérimntales des silicates fondus dans les systèmes FeO-SiO₂, PbO-SiO₂, FeO-CaO-SiO₂, FeO-MnO-SiO₂ et FeO-CoO-SiO₂. La correspondance est moins bonne lorsqu'on tend vers la composition du métasilicate, à cause de la présence des structures cycliques et groupées, non incluses dans les hypothèses. L'accroissement du volume molaire dû au groupelnent MSiO₃, tel que calculé à partir des données, varie entre 40 et 50 cm³ et augmente avec le rayon ionique du cation.     

Solubility of calcium in Fe-Ca-Xi melts

The equilibrium experiments on liquid Fe-Ca-X_i were carried out in a high pressure induction furnace in dense CaO crucibles. The solubility of calcium, saturated with CaO, in iron was determined as a function of temperature under 10 bar argon pressure. In pure iron the maximum solubility of calcium at 1 600°C is 0.03 wt.%. The alloying elements silicon, aluminium and nickel remarkably increase the calcium solubility in iron, whereas manganese causes an almost negligible increase. Chromium significantly reduces calcium solubility. The opposite influence of chromium and nickel on calcium solubility is balanced in an 18/8 steel. The interaction parameters of the alloying elements in the solvent iron with respect to Raoultian standard state are as follows:      

Activities and free energies of mixing in binary silicate melts

The thermodynamic properties of the Whiteway, Smith and Masson (WSM) models of polymerized silicate melts are calculated. The free energy is calculated as a function of composition and degree of polymerization of the silicate ions from heats of mixing and Guggenheim’s expression for the configurational entropy of a system of linear and branched chain polymer molecules in which random mixing of the mer units occurs. The variations, with composition, of the equilibrium degree of polymerization, the activities of solution components and the free energy of mixing are calculated as functions of the stability of the solid orthosilicate compound. Under the assumption of random mixing of the mer units, the thermodynamic properties are found to be independent of whether the SiO _in4 ^su4 ion is considered to be a bifunctional or tetrafunctional polymerizing unit. It is found that the apparent differences between the dependencies, on composition, of the ion fraction of O^2- in the WSM linear chain model and the WSM branching chain model are the result of the assumption, in these models, that random mixing of the anions occurs,i.e. that the systems exhibit Temkin behavior. It is suggested that the deviations of the theoretical free energies of mixing from experimental measurement, which begin when the mole fraction of silica is between 0.3 and 0.4, are due to the first significant appearance of ring ions in actual silicate melts at some composition within this range.