Iron-cobalt Melts Research Articles

Oxygen Solubility in the Hafnium-Containing Fe–Co Melts

A thermodynamic analysis of the oxygen solutions in the hafnium-containing Fe–Co melts is performed. The equilibrium constants of the deoxidation reaction of iron-cobalt melts with hafnium, the activity coefficients at infinite dilution, and the interaction parameters for melts differing in composition are determined. The dependences of the oxygen solubility in the melts under study on the cobalt and hafnium contents are calculated.

OXYGEN SOLUBILITY IN CARBON-CONTAINING Fe –Co MELTS

Thermodynamic analysis of oxygen solutions in carbon-containing Fe – Co melts has been carried out. The equilibrium constants of interaction of carbon and oxygen, the activity coefficients at infinite dilution, and the interaction parameters for melts of different composition at 1873 K were determined. The dependences of the oxygen solubility on the contents of cobalt and carbon in the studied melts were calculated. Carbon has a high affinity for oxygen in iron-cobalt melts. Deoxidation ability of carbon increases significantly with the increasing of cobalt content in the melt. Deoxidation ability of carbon in pure cobalt more than an order of magnitude higher than that in pure iron. Reaction products of carbon deoxidation are gaseous oxides – monoxide (CO) and carbon dioxide (CO 2 ). The interaction reaction of carbon and oxygen dissolved in the melt, and hence deoxidation ability of carbon depends on the total pressure of the gaseous phase above the melt. Deoxidation ability of carbon increases significantly with the gaseous phase pressure lowering. The minimum oxygen concentration achieved for alloys of the same composition decreased practically an order of magnitude at decrease 10 times the total pressure of the gaseous phase. The gaseous phase composition above Fe – Co melts and equilibrium carbon and oxygen concentrations in the melt at a total pressure of the gaseous phase P, of 1.0; 0.1 and 0.01 atm were calculated. Optimum oxygen concentration (1 – 10 ppm) in Fe – Co melts, depending on the total pressure of the gaseous phase (0.01 – 1 atm) is achieved at carbon contents from 0.01 to 1 %. The curves of the oxygen solubility in carbon-containing iron-cobalt melts pass through a minimum, which shifts toward lower carbon contents with increasing cobalt content in the melt. Further carbon additions leads to an increase in the oxygen concentration of the melt so that the higher cobalt content of the melt, the steeper the increase in the oxygen content after the minimum as carbon is added to the melt.

Oxygen Solubility in Fe–Co Melts Containing Carbon

In thermodynamic analysis of solutions of oxygen in Fe–Co melts containing carbon, the equilibrium constants of reactions between carbon and oxygen are determined, as well as the activity coefficients at infinite dilution and the interaction parameters in melts of different composition at 1873 K. The dependence of oxygen solubility in such melts on the cobalt and carbon content is calculated. In iron–cobalt melts, carbon has high oxygen affinity. The deoxidizing ability of carbon increase significantly with increase in cobalt content in the melt. In pure cobalt, it is more than an order of magnitude greater than in pure iron. Deoxidation by carbon produces gaseous oxides: carbon monoxide (CO) and dioxide (CO2). The reaction of carbon and oxygen dissolved in the melt and hence the deoxidizing ability of carbon depend on the total gas pressure above the melt. Decrease in gas pressure significantly improves the reducing properties of carbon. The minimum oxygen concentration for alloys of the same composition is reduced by practically an order of magnitude with tenfold decrease in the total gas pressure. The gas composition above Fe–Co melts and the equilibrium carbon and oxygen concentrations in the melt are calculated with total gas pressures of 1.0, 0.1, and 0.01 atm. The optimal oxygen concentration (1–10 ppm) in Fe–Co melts is reached at carbon concentrations between 0.01 and 1% depending on the total gas pressure (0.01–1 atm). The solubility of oxygen in iron–cobalt melts containing carbon passes through a minimum, which is shifted to lower carbon content with increase in the melt’s cobalt content. Further additions of carbon increase the oxygen concentrations in the melt. With increase in cobalt content, this increase will be sharper.

Production of alloys in the Fe–Co system with an oxygen concentration below 10 ppm

A fundamentally new solution of the challenge of producing alloys in the Fe–Co system with an oxygen concentration below 10 ppm (10–3%) has been for the first time justified and demonstrated. A thermodynamic analysis showed that decreasing the pressure of the gas phase over the melt significantly increases the deoxidizing power of carbon. At cobalt and carbon contents characteristic of soft- and hard-magnetic alloys and a total pressure of 0.01 atm, the oxygen concentration was 10–1 ppm (10–3–10–4%). With increasing cobalt content of the melt, the deoxidizing power of carbon increases. The curves of the oxygen solubility in carbon-containing iron–cobalt melts pass through a minimum, which shifts toward lower carbon contents with increasing cobalt content of the melt.

Solubility of oxygen in Fe–Co melts containing titanium

Solutions of oxygen in Fe–Co melts containing titanium are subjected to thermodynamic analysis. The first step is to determine the equilibrium reaction constants of titanium and oxygen, the activity coefficients at infinite dilution, and the interaction parameters in melts of different composition at 1873 K. With increase in cobalt content, the equilibrium reaction constants of titanium and oxygen decline from iron (logK(FeO · TiO2) =–7.194; logK(TiO2) =–6.125; logK(Ti3O5) =–16.793; logK(Ti2O3) =–10.224) to cobalt (logK(CoO · TiO2) =–8.580; logK(TiO5) =–7.625; logK(Ti3O5) =–20.073; logK(Ti2O3) =–12.005). The titanium concentrations at the equilibrium points between the oxide phases (Fe, Co)O · TiO2, TiO2, Ti3O5, and Ti2O3 are determined. The titanium content at the equilibrium point (Fe, Co)O · TiO2 ↔ TiO2 decreases from 1.0 × 10–4% Ti in iron to 1.9 × 10–6% Ti in cobalt. The titanium content at the equilibrium point TiO2↔Ti3O5 increases from 0.0011% Ti in iron to 0.0095% Ti in cobalt. The titanium content at the equilibrium point Ti3O5 ↔ Ti2O3 decreases from 0.181%Ti in iron to 1.570% Ti in cobalt. The solubility of oxygen in the given melts is calculated as a function of the cobalt and titanium content. The deoxidizing ability of titanium decline with increase in Co content to 20% and then rise at higher Co content. In iron and its alloys with 20% and 40% Co, the deoxidizing ability of titanium are practically the same. The solubility curves of oxygen in iron-cobalt melts containing titanium pass through a minimum, whose position shifts to lower Ti content with increase in the Co content. Further addition of titanium increases the oxygen content in the melt. With higher Co content in the melt, the oxygen content in the melt increases more sharply beyond the minimum, as further titanium is added.

Thermodynamics of oxygen solutions in titanium-containing Fe–Co melts

Performed for the first time, the thermodynamic analysis of oxygen solutions in titanium-containing Fe–Co melts showed that the deoxidizing power of titanium with increasing cobalt content of the melt first decreases, reaches a minimum at a cobalt content of 20%, and then increases. The titanium contents [%Ti]* at equilibrium points between the oxide phases TiO2, Ti3O5, and Ti2O3 were determined. The curves of the oxygen solubility in titanium-containing iron–cobalt melts pass through a minimum, which shifts toward lower titanium contents with increasing cobalt content of the melt. Further alloying with titanium leads to an increase in the oxygen concentration of the melt so that the higher cobalt content of the melt, the steeper the increase in the oxygen content after the minimum as titanium is added to the melt.

Thermodynamics of the oxygen solutions in boron-containing Fe–Co melts

A thermodynamic analysis of the oxygen solutions in boron-containing Fe–Co melts has been performed. The equilibrium constant of reaction between boron and oxygen, which are dissolved in iron–cobalt melts; the activity coefficients at infinite dilution; and the interaction parameters for melts differing in composition have been determined. The oxide phase formed in the Fe–Co melts containing boron and oxygen comprises FeO and CoO along with the B2O3 phase. The oxide phase compositions over Fe–Co–B–O melts are calculated. As the cobalt and boron contents in the melts increase, the mole fraction of boron oxide increases; in the case of pure cobalt, it is close to unity. The dependences of the oxygen solubility on the cobalt and boron contents in the melts are calculated. The deoxidizing capacity of boron substantially increases as the cobalt content in a melt increases. The composition dependences of the oxygen solubility in boron-containing Fe–Co melts have a minimum, which shifts to a low boron content as the cobalt content in the melts increases. The boron contents corresponding to the minimum in the oxygen solubility curves and the minimum oxygen concentrations corresponding to the boron contents are determined.

Thermodynamics of the oxygen solutions in chromium-containing melts of the Fe-Co system

Thermodynamic analysis of the oxygen solutions in chromium-containing melts of the Fe-Co system is carried out. The equilibrium constants for the interaction of chromium and oxygen, the activity coefficients at infinite dilution, and the interaction parameters in melts of various compositions are determined. The dependences of the oxygen solubility in the melts on the cobalt and chromium contents are calculated. Chromium in iron-cobalt melts is characterized by a fairly high oxygen affinity, which substantially increases with the cobalt content in a melt. The introduction of chromium into a melt in manufacturing ironcobalt alloys results in the final metal with a lower oxygen concentration. The solubility curves of oxygen in chromium-containing iron-cobalt melts pass through a minimum, whose position shifts toward low chromium contents as the cobalt content in a melt increases. Further chromium additives result in an increase in the oxygen concentration in a melt. The higher the cobalt content in the melt, the sharper the increase in the oxygen concentration after the minimum when chromium is added to the melt.

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.

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.

Thermodynamics of oxygen solutions in iron-cobalt melts

Thermodynamics of oxygen solutions in iron-cobalt melts