A mathematical model for estimation of sulphide capacities of multi-component slags

The present work presents mathematical model for the estimation of sulphide capacities. The sulphide capacity, C_S is expressed as (1) where ΔG⁰ is the standard Gibbs energy change for the reaction, (2) ξ, being a function of both temperature and composition, is characterized by the system under consideration. By optimizing ξ, the sulphide capacities could be estimated as functions of temperature and composition. The slag composition is described using a modified Temkin approach, where complex polymeric ions are considered as dissociated to simple species. The model has been applied to the binary systems CaO-SiO₂, MnO-SiO₂ as well as the CaO-MnO-SiO₂ ternary system. The results show that reliable predictions of the sulphide capacities can be obtained using the present model.     

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.     

Nitride capacities in CaO–SiO2 and CaO–SiO2–Al2O3 melts

Nitride capacities, , defined by (mass-% N) · in the CaO–SiO₂ and CaO–SiO₂–AI₂O₃ melts were measured in the temperature range of 1 723 to 1 923 K by a gas-slag equilibration technique using CaO, Al₂O₃, and Mo crucibles. Nitrogen content in slag, (mass-% N), was proportional to oxygen partial pressure, , to the power of ?3/4 at constant nitrogen partial pressure, . The values for increased linearly with increasing temperature and increased with the content of nitride formers, SiO₂ and Al₂O₃, but the effect of SiO₂ on value was found to be greater than that of Al₂O₃. The activity coefficients of Si_3/4N in the CaO–SiO₂ melts tended to increase with increasing the content of SiO₂.     

Equilibria of Ce-Al-O and Nd-Al-O in molten iron

Equilibrium of Ce-Al-O or Nd-Al-O system in molten iron was studied by separately melting radioactive isotope ¹⁴¹Ce or ¹⁴⁷Nd in an Al₂O₃ crucible filled with pure iron to form ¹⁴¹CeAlO₃ or ¹⁴⁷NdAlO₃ around its inner wall. The content of dissolved Ce or Nd in iron was determined by means of electrolysis in anhydrous electrolyte and radioassay. The concentration of dissolved Al in iron was obtained by photometry and followed by calculation. Activity of oxygen in liquid iron was directly measured by solid electrolyte sensors made of ZrO₂(MgO) tube. By extrapolation of data obtained, the temperature dependence of the equilibrium constant of RE-Al-O in molten iron, , or of interaction coefficient, may be described as:      

Measurement of aluminum or silicon activity in Fe-Ni (< 30 %) alloys using mullite and ZrO2-based solid electrolyte galvanic cell

Using mullite (3Al₂O₃·2SiO₂)-tube type and ZrO₂ (MgO mole fractions of 9 %)-plug type solid electrolyte, the activities of Al in the Fe-15, 29% Ni-0.002 to 0.84% Al (mass contents in%) alloys were measured at 1873 K in an Al₂O₃ crucible, and those of Si in the Fe-13, 28% Ni-0.13 to 2.3% Si alloys were measured at 1823 K in a mullite crucible with an excess of SiO₂. The interaction coefficients of and were determined as ?0.0173 ± 0.0052 and 0.00021 ± 0.00007, respectively, and those of and were determined as 0.0094 ± 0.0049 and ?0.00008 ± 0.00004, respectively. The oxygen activities obtained by the EMF measurements were compared with those obtained from the contents of analyzed oxygen. The oxygen activities in the Fe-Ni-Al alloys were found to be supersaturated. The interaction coefficients of and were determined as 0.0027 ± 0.0012 and 0.00012 ± 0.00004, respectively, from the contents of analyzed oxygen in Fe-Ni-Si alloys.     

Conventional chemical potentials of elements in dilute ferrous solution

Conventional thermochemical standard data are defined for dissolved elements i in iron. The standard partial enthalpy and entropy and in ideal dilute solution are described as simple temperature functions a_i and b_i are constants and denotes the partial molar heat capacity, which may be considered constant within a certain temperature range. From and further functions are derived, e.g. the conventional standard chemical potential and the modified Planck function β_i. The constants a_i, b_i, are evaluated and compiled for α-, γ, δ-iron as well as for liquid iron, as far as experimental data are available. In addition to the standard data the first order interaction coefficients for elements dissolved in liquid iron at 1873 K have been revised and tabulated.     

Korrekturverfahren für die Röntgenfluoreszenzanalyse hochlegierter Stähle

Untersuchung des Ansatzes auf seine Wirksamkeit zur Korrektur der Meßergebnisse. Erprobung an zahlreichen Werkzeugstählen und hochlegierten Stählen mit max. etwa 2% C, 1,4% Si, 1,7% Mn, 25% Cr, 25% Ni, 8% Mo, 3,5% V, 18% W, 5% Co, 0,3% Al, 0,5% Ti und 0,6% Cu. Fehlerabschätzung und Einsatz von Kleinrechnern zur schnellen Ermittlung des korrigierten Wertes.     

Untersuchung der ausscheidungsinduzierten magnetischen Nachwirkung in Fe-N-Legierungen mit verschiedenen Ausscheidungsstrukturen

Es wurde eine Fe-80 Gew.ppm-N-Legierung nach verschiedenen Anlaßbehandlungen mit Hilfe der magnetischen Nachwirkung untersucht, um den Effekt der Ausscheidungsstruktur auf die schon früher gefundenen Relaxationsprozesse⁶) ^{bis 8}) zu bestimmen. Es wurden zwei Prozesse gefunden: I. Diffusion im Spannungsfeld der Ausscheidung mit den mittleren Aktivierungsparametern Die Atome im Spannungsfeld erreichen ihre Gleichgewichtslage durch weitreichende Diffusion. Da dieser Effekt – ähnlich der hydrostatischen Relaxation bei Koiwa²⁶) – nur bei bestimmten geometrischen Konfigurationen der Blochwände und der spontanen Magnetisierung stattfindet und außerdem die Diffusion durch Versetzungen behindert werden kann, verschwindet diese Relaxation bei zunehmender Ausscheidungsgröße. Sie geht dann über in einen zweiten Reorientierungsprozeß, der im Spannungsfeld abläuft. Dieser hat wegen der Wechselwirkung mit den Versetzungen eine im Vergleich zur Richter-Nachwirkung erhöhte Aktivierungsenergie (1,10 eV). Für die Bindungsenergie der Stickstoffatome an die Oberfläche der Ausscheidungen findet man Werte im Bereich 0,3 … 0,5 eV, wobei die Stärke der Bindung mit wachsender Ausscheidungsgröße zunimmt. Dies weist darauf hin, daß die Versetzungen die Ausscheidungsoberfläche stabilisieren. II. Reorientierung der Stickstoffatome in der Randzone der Ausscheidung mit den mittleren Aktivierungsparametern Die Aktivierungsparameter werden von der Ausscheidungsstruktur kaum beeinflußt, ihre Verteilungen werden jedoch bei stabilisierten Ausscheidungen schärfer.     

Control of the aluminium-oxygen reaction in pure iron melts

Modified electrochemical oxygen sensors based on CaO-doped ZrO₂ and Y₂O₃-doped ThO₂ were developed and applied to study the aluminium-oxygen reaction in pure liquid iron with special regard to the provision of reliable experimental conditions and the attainment of true chemical equilibrium. The sensors represent valuable tools particularly for EMF long-term measurements over several hours. At 1600 °C, values of the constant and of the interaction parameters and were determined. When Fe-O-Al melts are covered with a slag phase at an activity a(Al₂O₃) < 1, e.g., CaO-saturated CaO-Al₂O₃ slag, the Al-O relationship in the iron may nevertheless be controlled by an equilibrium oxide phase at an activity a(Al₂O₃) = 1, presumably represented by inclusion particles consisting of pure Al₂O₃.     

On the reaction mechanism of the carburization and decarburization of α-iron in CH4/H2-mixtures

The surface reaction of the carburization and decarburization of α-iron in CH₄/H₂-mixtures has been investigated by a method using the radioactive isotope ¹⁴C. Experimentally two different kinetic equations have been confirmed and discussed in detail: In accordance to ¹) the kinetic equation (1) is explained by a slow reaction: . For the kinetic equation (2) the adsorption, respectively the desorption of CH₄, is considered to be the most slow partial step. The correlation of the carburization with the adsorption is supported by the relations: Thus can be regarded as E_a, the activation energy of the adsorption. Its value was determined at 109 kJ/mol being equivalent to 1.1 eV, which is characteristic for a chemisorption. Further it was established, that the rate of the decarburization according to equation (2) increases with decreasing temperature, i.e. the (apparent) activation energy proved to be negative. This is explained by the fact that before its rate-controlling desorption the CH₄-molecule first of all must be formed step-by-step and by the assumption that for thermodynamical reasons the surface concentration of CH₄ increases very much with decreasing temperature. The range of validity of the kinetic equations (1) and (2) can be limited to each other as follows:

• – The kinetic law (1) is established especially at higher H₂-pressures and at surfaces with low, but effective impurities. The impurities simultaneously result in a high decline of the reaction rate.
• – The kinetic law (2) is valid especially at lower H₂-pressures.

     

Structural statements,coordination numbers and water vapour solubility in aluminate slags

The IR emission of liquid CaO-Al₂O₃ slags is caused by IR active molecule vibrations of and -complexes. In the liquid CaO-Al₂O₃ slags the equilibrium dominates. At lower temperatures (1000°C) the formation of condensed -complexes was observed (glassy state). By the addition of B₂O₃ to CaO-Al₂O₃ slags B-O-Al associations were formed. Since the emission bands of the aluminate complexes overlap, a curve fitting with Gaussian functions was carried out to separate the bands. Furthermore, this quantitative evaluation leads to statements concerning the ratios between the different molecules. With the increase in temperature these associations are dissociated. In CaF₂-CaO-Al₂O₃ slags with higher contents of CaF₂, Al-O-F complexes with the coordination number 4 are present. Water vapour is dissoluted in liquid CaO-Al₂O₃ as hydroxide-ions (diffuse IR-emission-spectrum of ^?O-H^?…O^2?-molecule units).     

Control of the chromium-oxygen reaction in pure iron melts

Oxygen activities in Fe-O-Cr melts, equilibrated with chromium oxide, were determined as a function of chromium content by EMF measurements using ZrO₂(CaO) plug-type sensors with a Cr-Cr₂O₃ reference. Plug-type sensors with or without Cr₂O₃ saturator were used in the experiments. From the experimental results values for the activity coefficient f_O and the interaction parameters and were evaluated. Raoultian chromium activity features a slight positive deviation from ideal solution behaviour in the temperature range from 1550 to 1650°C. Taking into account the calculated interaction parameters, the equilibrium constant K_Cr-O was redetermined at 1550 to 1650°C. In comparison with previous studies a better agreement was obtained with existing thermochemical data.     

Thermodynamic behaviour of zinc in Fe‐C and CaO‐FeO‐CaF2 slag at high temperatures

The distribution ratio of zinc between Ag‐Zn and Fe‐Zn alloys was measured to clarify the thermodynamic behaviour of zinc in Fe‐C melt at high temperatures. Also, the distribution ratio between Ag‐Zn alloy and CaO‐FeO‐CaF₂ slag was measured to understand the dissolution mechanism of zinc in molten slags. The activity coefficient of zinc in Ag‐Zn alloy was preliminarily measured as a fundamental thermodynamic data for the activity of zinc in Fe‐C melt. From the dependence of the activity coefficient of zinc in Fe‐C melts on temperature and carbon content, the following equation could be obtained at 1473 ‐ 1623 K: The distribution ratio of zinc between Ag‐Zn alloy and CaO‐FeO‐CaF₂ slag increased by increasing both the oxygen potential and slag basicity. The stoichiometric coefficients of the dissolution reaction were obtained by considering the relationship between zinc distribution ratio and slag basicity or oxygen partial pressure, when one of these two independent variables was fixed. The dissolution reaction of zinc into the slags could be described as follows:      

Equilibrium between ammonia-hydrogen mixtures and the ε phase of iron

Foils made from pure iron with a porous structure were nitrided in mixtures of pure and entirely decomposed ammonia until constant weight was reached. The relationship between nitriding potential, temperature and concentration was measured in the ε region between 350 and 725°C and at concentrations between and . This relationship can be mathematically represented, if the ε phase is considered to be a subregular solution of nitrogen in hexagonal iron. From the Gibbs free energy of the nitrogen in the gas phase, the numerical relation and the parameters L′ = ? 600 000 + 775.6 T J/mole L″ = 1270000 ? 1423 T J/mole are deduced. The results of a calculation of the (γ + ε)/ε phase boundary using this equations are in accordance with an experimental measurement.     

Oxidation‐reduction equilibria of ferrous/ferric ions in oxide melts

Oxidation‐reduction equilibrium experiments were conducted with oxide melts containing CaO, Li₂O, Al₂O₃, ZnO, B₂O₃, SiO₂ and small concentrations of iron oxide. The results indicated that for compositions within the acidic regime, the ratio {(Fe³⁺)/(Fe²⁺) P_O2^1/4} decreased with an increase in basicity while for relatively basic melts, the ratio increased with an increase in basicity. This variation of {(Fe³⁺)/(Fe²⁺) P_O2^1/4} could be interpreted in terms of the optical basicity of the glass melts and is consistent with the following expressions for the red‐ox equilibria within acidic and relatively basic melts, respectively: In an acidic melt, the temperature dependence of the reaction yielded an enthalpy value which was in excellent agreement with the enthalpy change for the reaction: For a relatively basic melt, the enthalpy value for the corresponding reaction was about half of that found for the acidic melt.     

Thermodynamics of nitrogen in CaO-TiO2-TiO1.5 slags

The nitride capacities in CaO-TiO₂-TiO_1.5 slags, and nitrogen distribution ratio between these slags and liquid Cu (L_N = (mass-% N)/[mass-% N]) were measured by a gas-slag-metal equilibration technique, using a Mo crucible in the temperature range of 1823 to 1923 K under controlled partial pressures of oxygen and nitrogen . The values for , (mass-% Ti³⁺)/(mass-% Ti⁴⁺) ratio, and solubility of TiN in CaO-TiO₂-TiO_1.5 slags were obtained as a function of slag composition (X_CaO = 0.24 ～ 0.39) and temperature. Activity coefficients of TiN were evaluated from the values for activity coefficients of Ti in liquid Cu which were calculated from the results of TiN saturation experiments.     

Untersuchung des Verhaltens von Schwefel in kohlenstoffhaltigen Eisenschmelzen und der Wechselwirkung mit Kalk-Tonerde-Schlacke unter reduzierender Atmosphäre

Es wurde die Verteilung von Schwefel zwischen kohlenstoffhaltigen Eisenschmelzen und Schlacken des Systems CaO—Al²O³ bei Temperaturen bis 2000°C und ρ_co ≤ 1 bar untersucht. Es wird gezeigt, daß die Schwefelverteilung vom Partialdruck des Kohlenmonoxids und von der Temperatur abhängig ist. Für das System Eisen-Schwefel und ternäre Systeme mit Silicium und Mangan wurde die allgemeine Gesetzmäßigkeit für die Schwefelverdampfung in einem breiten Druckbereich von 10^?3 bis 10⁺³ mbar und bis 2000°C ermittelt. Es werden weiterhin unterschiedliche Mechanismen für die Entschwefelung diskutiert: Bei einem Druck von rd. 10^?3-10^?2 mbar ist die Diffusion durch die Diffusionsgrenzschicht in der Schmelze und bei 10^?1-10⁺³ mbar die Diffusion in der Gasgrenzschicht mit der chemischen Reaktion in der Gasphase geschwindigkeitsbestimmend. Im Druckbereich von 10^?2-10^?2 mbar existiert ein Zwischenbereich, in dem die Stoffübergangskoeffizienten in Schmelze und Gasphase gleiche Größenordnung besitzen.     

Thermodynamics of iron oxide in FexO‐dilute CaO + Al2O3 + SiO2 + FexO slags at 1873 K

The ferrous and ferric ion capacities, and , for the slag of CaO + Al₂O₃ + SiO₂ are determined at 1873 K by means of the distribution equilibrium of iron between Fe_xO dilute slags of the system and Pt + Fe alloys under a controlled atmosphere. Compared with the values of for CaO + Al₂O₃ binary slag at a constant ratio of Al₂O₃ to decreases with an increase in SiO₂ content. Nearly linear relationships are observed between the logarithm of the ferrous and ferric ion capacities and the optical basicity. Applying these capacities, the relationship between (%Fe^T) and PO₂ under iron saturation, as well as the iron redox equilibrium in slag in relation to the optical basicity were discussed.     

Solubilities of carbon in CaO-Al2O3-SiO2 slags saturated with liquid iron

By equilibrating the CaO-Al₂O₃-SiO₂ slags with Fe - 0.0003～0.07% Al - 0.002～3.5% Si - 0.9～2.0% C alloys (mass contents in %) at 1873 K, the solubilities of carbon were measured as a function of Si contents in metal, using an alumina or lime crucible. The distribution ratios of carbon as a C^2- -ion were found to be linearly related to Si contents with a slope of 1/2 at a given slag composition. The carbide capacity, , defined by (% C) , increased with increasing SiO₂ contents at a given CaO/AlO_1.5 molar ratio in the CaO-AlO_1.5SiO₂ system.     

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: