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:      

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.     

Some aspects on MgO solubility in complex slags

A magnesia capacity is defined, C_Mg²⁺ = (%Mg²⁺)/a_MgO and its relation to optical basicity is examined and discussed. The solubility of MgO in complex slags, in equilibrium with magnesiowustite, is derived from the activity of MgO in the magnesiowustite and from the magnesia capacity as given by the slag's optical basicity. It is found that the activity of MgO in the magnesiowustite can be derived from [%O] assuming ideality in the FeO–MgO system at 1600°C. It is also found that the MgO saturation contents in complex slags are accurately derived from the equation: In addition, the relation between the magnesia capacity and the capacities of vanadium and phosphorus is examined and the relative basicity of the oxides is discussed.     

Connection between diffusivity and activity coefficient

On the basis of linear nonequilibrium thermodynamics, the connection between diffusivity and activity interaction coefficients in melts was delineated and this relation can be expressed as the following mathematic formula: (1)     

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:      

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.     

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.     

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.

     

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:      

Solubility of nitrogen in austenitic FeCrMn alloys

The equilibrium solubility of nitrogen in austenitic iron-chromium, iron-manganese, and iron-chromium-manganese alloys with mass up to 20 % Cr and 18 % Mn was measured in the temperature range 1273 to 1473 K. The following interaction parameters were obtained: (1) Describing the effect of chromium and/or manganese on the nitrogen solubility by the excess term , the present measurements correspond satisfactorily to those of Hertzmann and Jarl and of Zheng in the system Fe-Cr-N, but they differ somewhat from values calculated by means of parameters published by Frisk. For the system Fe-Mn-N the present measurements correspond to measurements by Grabke et al. and to values calculated with parameters published by Qiu. Using parameters deduced from the present measurements in the austenitic Fe-Cr-Mn-N system similar nitrogen solubilities were calculated as Zheng had measured, but small deviations were found between the analysis by Qiu and this investigation.     

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.     

Kinetics of the carburization of iron alloys in methane-hydrogen mixtures and of the decarburization in hydrogen

The surface reaction kinetics have been investigated for the reaction CH₄ (gas) = C (dissolved) + 2H₂ (gas) on Fe and Fe-M foils (M = Mn, Cr, Co, Ni, Sn) at temperatures between 800 and 1000°C. The resistance relaxation method was applied in a flow apparatus. The following rate equation was observed for the rate of carbon uptake where is the carbon concentration and k and k′ are the rate constants for carburization and decarburization respectively. For Fe, Fe-10 Ni and Fe-10 Co the value of v = 3, for the alloys with > 20% Ni as well as for all Fe-Mn and Fe-Cr alloys the value v = 4 results from the measurements, which indicates differences in the rate determining step. With increasing Cr, Mn, Ni, Co content the rate constants k and k′ increase. The decrease of the equilibrium carbon concentration with increasing Ni content in Fe-Ni alloys is correlated to a fast increase of k′ and a slow increase of k with increasing Ni content. Beyond the minimum of at about 70 wt.% Ni both rate constants show a strong increase. By holding Ni at high carbon activities (a_C > 0.7 at 1000°C) segregation of carbon induces a surface reconstruction which is characterized by formation of (111) planes and which reduces the reaction rates. The increase of the equilibrium carbon concentration in the systems Fe–Mn and Fe–Cr with increasing content of alloying element is correlated to a slow increase of k′ and a fast increase of k with increasing Mn or Cr content. Sn segregates to the surface and retards the reaction rate by blocking the reaction sites for the surface reaction, similar to the effects of P and S.     

Reaction between CaO‐SiO2‐Al2O3 Slags and H2 + HCl + H2O Gas Mixtures

To better understand the thermodynamic behaviour of chlorine in blast furnaces, CaO‐SiO₂‐Al₂O₃ slags were brought into equilibrium with Ar + H₂ + HCl + H₂O gas mixtures at temperatures between 1673 K and 1798 K. The dissolution of chlorine into molten slags could be well interpreted through a reaction: (1/2) {CaO}_slag + (HCl) = {Ca_1/2Cl}_slag + (1/2) (H₂O). Conforming to this formula, a linear relation was observed between log (%CI) and log with an anticipated slope of 1/2.     

Activities of FexO in CaO + CaF2 + SiO2 + FexO quaternary slags by disposable electrochemical oxygen probes

The activities of Fe_xO in CaO + CaF₂ + SiO₂ + Fe_xO quaternary slags were measured by means of solid-oxide galvanic cell. The Fe_xO activities in the slags are influenced by CaF₂ as well as SiO₂. At constant Fe_xO mole fractions, e.g., , at low SiO₂ mole fractions i.e., , the substitution of CaF₂ for CaO has an effect of raising the Fe_xO activity. At higher SiO₂ mole fractions, e.g., , however, such an effect becomes insignificant.     

Thermochemische Kennwerte für die Reaktion,Mo + O2 ⇌ MoO2 sowie in Eisenschmelzen

Zusammenstellung von Schrifttumsangaben für die Änderung der freien Standardenthalpien der Reaktionen , Mo + O₂ ? MoO₂ und in Eisenschmelzen. Neubestimmung der Temperaturabhängigkeiten der Größen ΔG^oCr₂O₃, ΔG^oMoO₂ und ΔG^o_O im Eisen bei Temperaturen zwischen 1460 bzw. 1530 und 1725 °C. Nachweis der Anwendbarkeit der neu ermittelten thermodynamischen Funktionen durch EMK-Parallelmessungen an ThO₂ (Y₂O₃)- und ZrO₂ (MgO)-Festelektrolytzellen mit Cr-Cr₂O₃- und Mo-MoO₂-Referenzelektroden in Reineisenschmelzen bei 1600 °C. Ermittlung des Parameters p_e′ der Elektronenteilleitfähigkeit für einen teilstabilisierten ZrO₂-Festelektrolyten mit einem Stoffmengengehalt von 5% MgO.     

Approaching (100)<0vw> by Rolling Directionally Solidified Silicon Steels

Based on the possible ability of strip casting to produce a (100)<0vw> fibre texture by directional solidification, experiments of rolling, annealing and magnetic measurement were performed on samples that were directionally solidified by other means. Samples with a final texture of strong (001) component were obtained in steels with 3 wt.% Si and 0.2 wt.% Al. A B₅₀ value of 1.71T was obtained in a as‐cast ring specimen. Starting samples have columnar grains with a diameter of about 1mm diameter tilted about 9°, on the average, relative to a perfect <100>//ND. Cold rolling produced the expected rotated cube (001)<>. Further processing steps led to the final texture mentioned above. The paper presents the texture evolution along the processing steps.     

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.     

Thermodynamics of phosphorus and sulfur in the BaO-MnO flux system between 1573 and 1673 K

The oxidative dephosphorization of carbon-saturated Fe-Mn alloys was successfully demonstrated by measuring the phosphorus partition ratio between BaO-MnO, BaO-MnO-BaF₂, and BaO-CaO_satd.-MnO fluxes and liquid Fe-Mn-C_satd. alloy between 1573 and 1673 K. The phosphorus partition ratio increases with increasing BaO content of the flux. The phosphate capacity of the BaO-MnO flux is as high as that of the BaO-BaF₂ flux and is far larger than those of CaO-bearing fluxes. Addition of BaF₂ to the BaO-MnO flux increases BaO solubility, which increases the phosphate capacity. The manganese partition ratios between the BaO-MnO flux and Fe-Mn-C_satd. alloy were approximately constant at 0.64, 0.33, and 0.23 at 1573, 1623, and 1673 K, respectively. The carbon content of the BaO-MnO flux was measured as functions of slag composition, temperature, and partial pressure of CO. A stable species of carbon in the BaO-MnO flux was found to be BaC₂ experimentally and thermodynamically. The sulfide capacity of the BaO-MnO system at 1573 K has been shown to be far larger than any known flux systems and to be a few times larger than that for the BaO-BaF₂ system. Formerly Graduate Student, Department of Metallurgy, The University of Tokyo     

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.