Local atomic order in the Al-Cu-Fe melts corresponding to crystalline and quasicrystalline phases

The local atomic order in the Al₇₀Cu₂₀Fe₁₀ and Al_61.9Cu_25.4Fe_12.7 melts that correspond to the tetragonal τ₂ and quasicrystalline phases was studied. The structures of these ternary melts were investigated by high-temperature X-ray diffraction and Reverse Monte Carlo simulation at various temperatures. The structural models of the melts are analyzed using the Voronoi polyhedra and the Delaunay simplexes. The specific features in the structure factor curves were comprehensively discussed: a shoulder in the second maximum and a prepeak on the left side of the principal maximum. The prepeak in the structure factor curves in the diffraction vector range 11–22 nm^?1 is shown to be caused by chemical local atomic ordering, and the shoulder on the right side of the second maximum is shown to result from the presence of icosahedral polytetrahedral clusters in the melts.     

A Chemical Approach of the Molecular Entity Vacancy Model to the CaO‐Al2O3‐SiO2 Ternary Silicate Melt

A chemical approach of the molecular entity vacancy model (MEVM) to the CaO‐Al₂O₃‐SiO₂ ternary silicate melts has been suggested. The activities of all components in the melts were simultaneously predicted by using only the binary parameters of its sub‐binary melts which were determined by fitting the activities of their two components. The results indicated that the predicted values of activity of SiO₂ were in good agreement with the experimental data at both temperatures 1823 K and 1873 K, and those of CaO and Al₂O₃ were in reasonable agreement with the experimental data at 1823 K and were smaller than the graphical integration data of the Gibbs‐Duhem equation at 1873 K. The approach may be extended to some solution systems with the chemical interaction.     

A Pseudo-Multicomponent Approach to Important Ternary Silicate Melts

For the CaO-Al₂O₃-SiO₂, CaO-FeO-SiO₂, and MnO-FeO-SiO₂ ternary silicate melts, there are few models that can accurately predict their component activities. One model that can make a good correlation between the ternary activities and their sub-binary ones is a pseudo-multicomponent approach based on the molecular interaction volume model (MIVM). It does not need any linear or power series composition functions of binary parameters and also does not require any ternary adjustable parameters in addition to its composition equation. The results show that in the CaO-Al₂O₃-SiO₂ system, the predicted values of SiO₂ activity are in good agreement with the experimental data at 1873?K (1600?°C), and those of CaO and Al₂O₃ are in reasonable agreement with the graphical integration of data using the Gibbs?CDuhem equation at 1873?K (1600?°C) and experimental data at 1823?K (1550?°C). In the CaO-FeO-SiO₂ and MnO-FeO-SiO₂ systems, the predicted values of FeO and MnO activity are in good agreement with the experimental data, and those of CaO and SiO₂ are in reasonable agreement with the experimental data at 1823?K, 1873?K, and 1803?K (1550?°C, 1600?°C, and 1533?°C).     

Microstructure and mechanical properties of ternary intermetallic compound dispersed P/M Al-Mn-X-Zr (x=Cu,Ni) alloys

Heat-resistant aluminum alloys are generally developed by dispersing stable intermetallic compounds by adding transition metals (TM) whose diffusion coefficient in aluminum alloys is low even at high temperatures. Commonly used intermetallic compounds include Al-TM binary intermetallic compounds, for example, Al₆Fe, Al₃Ti and Al₃Ni. By contrast, multicomponent intermetallic compounds are hardly used. The present study focuses on Al-Mn-Cu and Al-Mn-Ni ternary intermetallic compounds, and by finely dispersing these intermetallic compounds, attempts to develop heat-resistant alloys. Through the atomization method, Al-(4.96–5.96)Mn-(6.82–7.53)Cu-0.4Zr and Al-(5.48–8.76)Mn-(2.23–4.32)Ni-0.4Zr (in mass%) powders were fabricated, and by degassing these powders at 773 K, intermetallic compounds were precipitated. These powders were then solidified into extrudates by hot extrusion at 773 K. The microstructural characterization of powders and exrudates was carried out by XRD analysis, SEM/EDX and TEM. The mechanical properties of extrudates were determined at room temperature, 523 K and 573 K. In Al-Mn-Cu alloys, while a small amount of Al₂Cu was crystallized, precipitated Al₂₀Mn₃Cu₂ intermetallic compounds were mainly dispersed. In Al-Mn-Ni alloys, while a small amount of Al₆Mn intermetallic compounds was precipitated, the precipitated A₆₀Mn₁₁Ni₄ intermetallic compounds were mainly dispersed. Both ternary intermetallic compounds were about 200 nm in size. The compounds were elliptical, and their longitudinal direction was oriented along the extrusion direction. In the Al-Mn-Cu alloys, since the work hardening at room temperature was high, the tensile strength became 569 MPa. At elevated temperatures, since hardly any work hardening was observed, the tensile strength decreased markedly. However, in Al-Mn-Ni alloys, since the work hardening is low even at room temperature, the roomtemperature strength is not high. Thus, the decrease in tensile strength at elevated temperatures is relatively small and a high strength was obtained at 523 K and 573 K: 276 MPa and 207 MPa, respectively.     

Modeling the Viscosity of Silicate Melts Containing Lead Oxide

Our recently developed model for the viscosity of silicate melts is applied to describe and predict the viscosities of oxide melts containing lead oxide. The model requires three pairs of adjustable parameters that are fitted to the experimental viscosities in the following systems: pure PbO, PbO-SiO₂, and PbO-Al₂O₃-SiO₂. The viscosity of other ternary and multicomponent silicate melts containing PbO is then predicted by the model without any additional adjustable model parameters. Experimental viscosity data are reviewed for melts formed by PbO with SiO₂, Al₂O₃, CaO, MgO, Na₂O, and K₂O. The deviation of the available experimental data from the viscosities predicted by the model is within experimental error limits.     

Short- and medium-range orders in Al-Mn melts

The structures of Al-Mn melts with 14.3, 20, 26.7, 40, 50, and 70 at % Mn are studied by X-ray diffraction at a temperature 50°C above the liquidus temperature. The reverse Monte Carlo simulation and experimental structure-factor curves are used to construct structural models for liquid Al, Mn, and their binary melts. The character of atomic ordering on short- and medium-range scales is studied by dividing model configurations into Voronoi polyhedra and Delaunay simplexes. A nonmonotonic dependence of structural parameters is found in the region with a high aluminum content. The structural parameters have extremum values in an Al₆Mn melt. The prepeak in the structure-factor curves in the diffraction vector range 9–25 nm⁻¹ is shown to be caused by a chemical atomic order in polytetrahedral clusters.     

Microstructural characterization of the dispersed phases in Al-Ce-Fe system

Analytical electron microscopy studies were conducted on a rapidly solidified Al-8.8Fe-3.7Ce alloy and arc melted buttons of aluminum rich Al-Fe-Ce alloys to determine the characteristics of the metastable and equilibrium phases. The rapidly solidified alloy consisted of binary and ternary metastable phases in the as-extruded condition. The binary metastable phase was identified to be Al₆Fe, while the ternary metastable phases were identified to be Al₁₀Fe₂Ce and Al₂₀Fe₅Ce. The Al₂₀Fe₅Ce was a decagonal quasicrystal while the Al₁₀Fe₂Ce phase was determined to have an orthorhombic crystal structure belonging to space group Cmmm, Cmm2, or C222. Microscopy studies of RS alloy and cast buttons annealed at 700 K established the equilibrium phases to be Al₁₃Fe₄, Al₄Ce, and an Al₁₃Fe₃Ce ternary phase which was first identified in the present study. The crystal structure of the equilibrium ternary phase was determined to be orthorhombic with a Cmcm or Cmc2 space group. The details of X-ray microanalysis and convergent beam electron diffraction analysis are described.     

The dissolution of aluminum oxide in cryolite melts

Several modifications of Al₂O₃ were prepared. Al₂O₃ samples pressed to tablets were dissolved in cryolite melts at temperatures between 975 and 1090°C. The dissolution rates obtained are consistent with the consecutive occurrence of two rate laws. The dissolution rate changes at an Al₂O₃ content of 5 to 6 pct in the cryolite melts. The results are discussed with consideration of other experimental and theoretical work. It is concluded that the alteration of the rate law may be explained by structural changes in the melts.     

Experimental studies of the viscosities in the CaO-Fe n O-SiO2 slags

In the present work, the viscosities in the CaO-Fe _n O-SiO₂ ternary system have been measured by the rotating cylinder method involving a spindle and crucible made of iron. Nine slag compositions in the ternary system have been chosen with CaO varying between 5.5 and 45.5 pct mass, FeO between 10.0 and 70.0 pct mass, and one measurement each in the binary Fe _n O-SiO₂ and CaO-SiO₂ melts. The measurements have been carried out in the temperature range of 1423 to 1753 K. The viscosity in this system is described as a function of temperature and composition using the model approach developed earlier at the present laboratory. The isoviscosity lines have been predicated at 1573, 1673, and 1723 K. Good agreement between the calculated results and the experimental data has been obtained.     

Interaction of exogenous refractory nanophases with antimony dissolved in liquid iron

The heterophase interaction of Al₂O₃ refractory nanoparticles with a surfactant impurity (antimony) in the Fe–Sb (0.095 wt %)–O (0.008 wt %) system is studied. It is shown that the introduction of 0.06–0.18 wt % Al₂O₃ nanoparticles (25–83 nm) into a melt during isothermal holding for up to 1200 s leads to a decrease in the antimony content: the maximum degree of antimony removal is 26 rel %. The sessile drop method is used to investigate the surface tension and the density of Fe, Fe–Sb, and Fe–Sb–Al₂O₃ melts. The polytherms of the surface tension of these melts have a linear character, the removal of antimony from the Fe–Sb–Al₂O₃ melts depends on the time of melting in a vacuum induction furnace, and the experimental results obtained reveal the kinetic laws of the structure formation in the surface layers of the melts. The determined melt densities demonstrate that the introduction of antimony into the Fe–O melt causes an increase in its compression by 47 rel %. The structure of the Fe–Sb–O melt after the introduction of Al₂O₃ nanoparticles depends on the time of melting in a vacuum induction furnace.     

Effect of titanium and molybdenum oxides on viscosity and electrical conductivity of oxide-fluoride slags

The effect of additives of titanium and molybdenum oxides on the viscosity and electrical conductivity of the Al₂O₃-CaO-CaF₂ oxide-fluoride slag melts at 1750–1950 K is investigated by vibration viscosimetry and the ac bridge method. Crystallization intervals are established depending on the variation in the TiO₂ and MoO₃ concentrations in the melts from 0 to 25%, and it is revealed that the majority charge carriers are calcium and fluorine ions. These data indicate the complex-forming character of the behavior of Ti and Mo in aluminum-calcium oxide-fluoride melts.     

Deoxidation with silicon and the control of oxide inclusions in electrical steels

The oxygen solubility in Fe-Si melts in equilibrium with SiO₂ at 1873 K has been determined in a concentration range of 0.1–70 wt % Si. Model alloys are melted in quartz crucibles in an argon atmosphere. The oxygen content in analytical samples is determined by the inert-gas reducing-fusion method after careful sample preparation. The results obtained have been processed using a thermodynamic model that can calculate the oxygen activity and solubility in Fe-Si melts up to 100 wt % Si. The effects of the heating rate and the silicon content on the carbon concentration in carbonyl iron and Fe-Si alloys are studied using the inert-gas reducing-fusion method in the temperature range 1673–2373 K. Oriented electrical steels are investigated using fractional gas analysis. The main forms of oxygen in these steels are found to be silicates, Al₂O₃, and MgAl₂O₄.     

The activity coefficients of oxygen in Ni-S and Co-S melts

Activity coefficients of oxygen,γ _o, in nickel-sulfur melts and cobalt-sulfur melts were determined at 1423 K utilizing a modified coulometric titration technique with the following electrochemical cell: O in Ni-S or Co-S melt/ZrO₂(+CaO)/air, Pt. Theγ _o values around N_NI=0.26 and N_CO=0.35 are much smaller than those in the hypothetically undercooled liquid nickel and cobalt, respectively, at 1423 K, which were evaluated by extrapolating the literature values at higher temperatures. Theγ _o values in the nickel-sulfur and cobalt-sulfur melts are rapidly increased with increasing the sulfur compositions. The shapes of the Inγ _o vs solvent composition curves are quite similar to those in Cu-S, Cu-Te, and Tl-Te melts. The present results are discussed in terms of several solution models. former name, SHINYA OTSUKA Formerly Graduate Students, Osaka University     

Synthesis of Al-Zr Alloys <Emphasis Type="Italic">Via</Emphasis> ZrO<Subscript>2</Subscript> Aluminum-Thermal Reduction in KF-AlF<Subscript>3</Subscript>-Based Melts

Physical–chemical investigations of KF-AlF₃ melts were carried out in order to develop the scientific basis of the technology for Al-Zr alloy synthesis. The possibility of Al-Zr alloy synthesis via the aluminum-thermal method was shown. The liquidus temperatures of KF-AlF₃ and KF-NaF-AlF₃ melts with additions of Al₂O₃ and ZrO₂ were determined using the thermal analysis method in the temperature range from 873 K to 1173 K (600 °C to 900 °C). The dependency of the solubility of ZrO₂ in KF-AlF₃ and KF-NaF-AlF₃ melts on Al₂O₃ concentration was measured.     

Effect of exogenous refractory nanophases on the structural properties of nickel melts

The surface tension and density of nickel and Ni-S melts containing Al₂O₃ and TiN refractory-phase nanoparticles (RPNPs) are studied by the sessile drop method using a digital camera and computer processing of images. The dependences of the structural properties of Ni, Ni-(Al₂O₃,TiN), Ni-S, and Ni-S-(Al₂O₃,TiN) melts on temperature and the type and size of RPNPs are determined. It is found that the surface tension decreases with increasing temperature, the temperature dependence of the surface tension is inverted, the degree of loosening in the Ni-S-(Al₂O₃,TiN) melts decreases, and Ni-S-RPNP ensembles affect the melt structure.     

A thermodynamic model for calculating manganese distribution ratio between CaO–SiO2–MgO–FeO–MnO–Al2O3–TiO2–CaF2 ironmaking slags and carbon saturated hot metal based on the IMCT

A thermodynamic model (IMCT-L_Mn) for calculating manganese distribution ratio between CaO–SiO₂–MgO–FeO–MnO–Al₂O₃–TiO₂–CaF₂ slags and carbon saturated liquid iron have been developed based on the ion and molecule coexistence theory. The predicted manganese distribution ratio shows a reliable agreement with the measured ones. With the aid of the IMCT-L_Mn model, the respective manganese distribution ratio of (Mn²⁺?+?O^2?), MnO·SiO₂, 2MnO·SiO₂, MnO·Al₂O₃, MnO·TiO₂, and 2MnO·TiO₂ are investigated. The results indicate that the structural units SiO₂?+?FeO play a key role in CaO–SiO₂–MgO–FeO–MnO–Al₂O₃–TiO₂–CaF₂ slags in demanganisation process in the course of hot metal treatment at 1673?K. The manganese distribution ratio at a given binary basicity range increases with CaF₂ content, while that decreases with TiO₂ content at different binary basicity scopes, which demonstrate that high Mn in the metal is favoured by TiO₂ content. In the present study, various critical experiments are carried out in an effort to clarify the effect of temperature on demanganisation ability, indicating that the lower temperature of molten metal is, the faster the rate of demanganisation reaction is and the shorter the thermodynamic equilibrium time is and the lower end-point Mn content is. It can be deduced from the obtained experimental results that the greater oxygen potential of slags or iron-based melts, lower content of basic oxides in slags, and lower temperature at reaction region is benefit for demanganisation reaction.     

Activities in MnO-SiO2-AI2O3 slags and deoxidation equilibria of Mn and Si

The activities of MnO and SiO₂ along the liquidus line in the MnO-SiO₂-Al₂O₃-Fe_tO (1.2 to 6.7 mass pct) system were determined at 1823 and 1873 K by using a slag-metal equilibration technique. On the basis of the re-evaluated MnO iso-activity curves, the SiO₂ and Al₂O₃ iso-activity curves were determined by using the ternary Gibbs-Duhem relation. The control of inclusions composition in Si-Mn killed steels is discussed based on the equilibria between inclusion and steel with respect to Si, Mn, Al, and O.     

Structure and mechanical properties of boron-doped cubic zirconium trialuminides

Cubic (L1₂) ternary zirconium trialuminides macroalloyed with Cu(Al₅CuZr₂), Mn(Al₆₆Mn₉Zr₂₅), and Cr(Al₆₇Cr₈Zr₂₅) (atomic percent) and doped with 50 and 100 ppm boron were fabricated by induction melting. Their as-cast microstructures are characterized by a small amount of porosity (1 to 2 pct) and second phase (2 to 3 pct). Boron seems to slightly enhance porosity (up to 3.3 pct) in Al₅CuZr₂ +100 ppm B alloy, and it also promotes some compositional inhomo-geneity in Al₆₆Mn₉Zr₂₅ alloy. Vickers microhardness and compressive properties at room temperature (RT), peak strength temperature (500 °C to 600 °C) and 900 °C were investigated. Microcracking development was also investigated in Al₅CuZr₂ +100 ppm boron alloy exhibiting a stepped load-deflection curve. Vickers microhardness strongly depends on load, similarly to boron-free cubic ternary zirconium and titanium trialuminides, and increases in a systematic way with increasing boron content which seems to indicate a solid solution strengthening effect. At RT, 0.2 pct offset yield strength is not increased by the boron doping in most of the alloys studied except for Al₆₆Mn₉Zr₂₅ + 50 ppm B alloy. Permanent deformation (apparent ductility) at ultimate compressive strength is not enhanced by boron doping. In Al₅CuZr₂ +100 ppm B alloy microcracks start nucleating and proliferating in the elastic region of load-deflection curve in characteristic “bursts” accompanied by a “click” sound and the appearance of a discernible step on the load-deflection curve. Pre-existing pores are observed to be active centers of microcracking.     

Electrochemical Removal of AlCl3 from LiCl-KCl Melts

In order to remove impurity AlCl₃ from LiCl-KCl melts before Li electrolysis, the Al³⁺ reduction potential on a tungsten electrode and the relation between Al³⁺ reduction peak current and AlCl₃ concentration in LiCl-KCl-AlCl₃ melts were determined by cyclic voltammetry (CV). Constant potential electrolysis at –1.6 V vs Cl₂/Cl^– on both solid Fe and liquid Zn cathodes was performed to remove AlCl₃ impurity from the LiCl-KCl-AlCl₃ melts. The removal rate of Al³⁺ from the melts was analyzed by both electrochemical methods and inductively coupled plasma–atomic emission spectrometry (ICP-AES) analysis. The results showed that 96.11 wt pct of Al were removed on a Fe cathode and 99.90 wt pct on a Zn cathode through 10 hours electrolysis, respectively. While stirring the melts by argon gas, 99.21 wt pct of Al³⁺ was separated from the melts by 4 hours of electrolysis at 723 K (450 °C), which effectively expedited the Al³⁺ electrochemical reduction rate and shortened the electrolysis time.