Analysis of the Zn-Se system

The Zn-Se phase diagram is reanalyzed with an associated solution model for the liquid, new Se-rich liquidus points, and a new Gibbs energy of formation for ZnSe(s). After the liquid model parameters are fixed by a best fit to the liquidus points, the entire liquidus is generated as well as the partial pressures of Zn and of Se₂ along the ZnSe(s) three-phase curve, isotherms for the enthalpy of mixing, and the isotherm for the activity coefficients at the 1799 K melting point of ZnSe(s).     

Calculation of Two-Dimensional Sections of Liquidus Projections in Multicomponent Systems

A two-dimensional (2D) section of liquidus projection consists of univariant lines of three-phase equilibria between liquid and other phases. It is useful not only for people’s easy visualization but also for retaining important information about the multicomponent liquidus surface, which is critical for understanding and controlling the solidification microstructure. An algorithm is presented for calculating two-dimensional sections of liquidus projections for multicomponent systems. It can project a liquidus surface onto any given two-dimensional section in the compositional space. A hypothetical quaternary system is designed to illustrate the features of the 2D sectional liquidus projections. Then the Nb-Ti-Si-Cr system is used as an example to demonstrate how to apply a 2D sectional liquidus projection to determine the amount of Cr addition into Nb-Ti-Si alloy to affect the liquidus surface of the quaternary system.     

Calculations of phase diagrams in associated solution model

The development of an ideal associated solution model concerned with complexes of various compositions, sizes, and shapes is described. Such models were used earlier to calculate thermodynamic characteristics and the position of the liquidus line for binary eutectic systems as well as those having a stable compound in the solid phase. In all the cases, the model parameters were not adjusted but were estimated from melting temperatures of the components. The latest studies deal with the influence of arbitrary stoichiometry associates on the equilibrium thermodynamic properties of liquid alloys. The application of the model to eutectic systems and systems having an unlimited miscibility in solid and liquid states close to the liquidus has been considered. It was shown that if the difference in melting temperatures of the components was small, different types of fusibility diagrams were possible: eutectic diagrams, cigar-shaped diagrams, or diagrams with upper or lower azeotropic points. Peritectic transformations could take place if the difference in melting temperatures of the components were large.     

Thermodynamic evaluation and optimization of the Ca−Si system

All available phase equilibria and thermodynamic data for the Ca−Si system were collected and critically evaluated. In a first step, the thermodynamic properties of Ca(g) were obtained from experimental vapor pressure data over pure Ca. The new vapor pressure of calcium over pure solid and liquid was used as a new reference to model the thermodynamic properties of the intermediate stoichiometric Ca−Si compounds together with other thermodynamic and phase diagram data found in the literature (liquidus temperatures, heat capacities, pressures of Ca, and heats of reaction). Optimization was performed to obtain the parameters of one set of model equations for the different solid and liquid phases to best reproduce all the experimental data simultaneously. In this way, the data are rendered self-consistent, discrepancies among the data are identified, and extrapolations and interpolations can be performed. For the liquid phase, the Modified Quasichemical Model in the Pair Approximation for short-range ordering was used.     

Experimental Study and Thermodynamic Re-optimization of the FeO-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript> System

Phase equilibria and thermodynamic data in the FeO-Fe₂O₃-SiO₂ system were critically reviewed. New experiments were undertaken to resolve discrepancies found in previous data. The liquid oxide/slag phase was described using the modified quasichemical model. New optimized parameters of the thermodynamic models for the Gibbs energies of slag and other phases in the selected system were obtained. The new parameters reproduce all available phase equilibria and thermodynamic data within the experimental error limits from 298 K (25 °C) to above the liquidus temperatures at all compositions and oxygen partial pressures from metal saturation to 1 atm of O₂. This study was carried out as part of the development of a self-consistent thermodynamic database for the Al-Ca-Cu-Fe-Mg-Si-O-S multi-component system.     

Experimental investigation of phase equilibria and thermodynamic modeling of the CaO–Al2O3–CaS and the CaO–SiO2–CaS oxysulfide systems

Phase equilibria of the CaO–Al₂O₃–CaS and the CaO–SiO₂–CaS systems were experimentally investigated using equilibration and quenching techniques. Equilibrium phases were analyzed by means of electron probe X-ray microanalysis, X-ray diffraction analysis and differential thermal analysis. Solubility limits of all solid phases in these liquid oxysulfide phases were successfully constructed in the temperature range investigated in the present study (1500–1600 °C). In order to supplement understanding the phase equilibria, a thermodynamic modeling of these liquid oxysulfides was conducted by taking into account strong chemical short-range ordering (SRO) in the framework of the modified quasichemical model in the quadruplet approximation. As for the solubility of CaS in the liquid oxysulfides, the solubility increases with increase in CaO in the case of the CaO–Al₂O₃–CaS system, whereas it decreases with increase in CaO in the case of the CaO–SiO₂–CaS system. Such opposite behavior is explained by differences in the effect of the SRO in different liquid phases. It is shown that consideration for the SRO in the thermodynamic modeling is essential in order to properly describe the Gibbs energy of the liquid oxysulfide phase. Using the thermodynamic model and the database developed in the present study, liquidus projections of these oxysulfide systems are proposed for the first time.     

Phase equilibria in the Fe–Al–Nb system: Solidification behaviour,liquidus surface and isothermal sections

The Fe–Al–Nb phase diagram including isothermal sections at 1000, 1150, and 1300 °C as well as the liquidus surface and corresponding reaction scheme was studied experimentally by a combination of scanning electron microscopy (SEM), electron probe microanalysis (EPMA), X-ray diffraction (XRD), and differential thermal analysis (DTA). No genuinely ternary intermetallic phase exists in the system, but the two Fe–Nb phases NbFe₂ (C14-type Laves phase) and Fe₇Nb₆ (μ phase) have extended homogeneity ranges in the ternary system, where large amounts of Fe can be substituted by Al in both cases. The solubility of the third element was studied for all binary phases and the effect on the lattice parameters is discussed. From analysis of the as-cast microstructures and DTA experiments, the liquidus surface including all invariant reactions as well as the occurring solid state reactions were established. Three ternary eutectics, one eutectoid, and two peritectic reactions were found, and the list of invariant points is completed by seven U-type reactions.     

The influence of shear rate and temperature on the viscosity and fragility of the Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 metallic-glass-forming liquid

The shear rate and temperature dependence of the viscosity in the Zr_41.2Ti_13.8Cu_12.5Ni_10.0Be_22.5 bulk metallic-glass-forming liquid has been measured in the liquid and undercooled liquid state between 907 and 1300 K. After quenching the alloy into a glassy state, the reheated material displays very high viscosity values above the liquidus temperature of 1026 K. This liquid alloy is kinetically strong with pronounced shear thinning. With increasing temperature a transition to a more fragile liquid is observed with a drastic drop in viscosity that is associated with the disappearance of shear thinning. This fragile state is attained above 1225 K. When cooled from this state the strong state is only recovered when the liquid is deeply undercooled below the liquidus temperature. The shear thinning and strong to fragile transition is attributed to the destruction of medium- and short-range order in the liquid by mechanical and thermal effects, respectively.     

Understanding Slag Freeze Linings

Slag freeze linings, the formation of protective deposit layers on the inner walls of furnaces and reactors, are increasingly used in industrial pyrometallurgical processes to ensure that furnace integrity is maintained in these aggressive, high-temperature environments. Most previous studies of freeze-linings have analyzed the formation of slag deposits based solely on heat transfer considerations. These thermal models have assumed that the interface between the stationary frozen layer and the agitated molten bath at steady-state deposit thickness consists of the primary phase, which stays in contact with the bulk liquid at the liquidus temperature. Recent experimental studies, however, have clearly demonstrated that the temperature of the deposit/liquid bath interface can be lower than the liquidus temperature of the bulk liquid. A conceptual framework has been proposed to explain the observations and the factors influencing the microstructure and the temperature of the interface at steady-state conditions. The observations are consistent with a dynamic steady state that is a balance between (I) the rate of nucleation and growth of solids on detached crystals in a subliquidus layer as this fluid material moves toward the stagnant deposit interface and (II) the dissolution of these detached crystals as they are transported away from the interface by turbulent eddies. It is argued that the assumption that the interface temperature is the liquidus of the bulk material represents only a limiting condition, and that the interface temperature can be between T _liquidus and T _solidus depending on the process conditions and bath chemistry. These findings have implications for the modeling approach and boundary conditions required to accurately describe these systems. They also indicate the opportunity to integrate considerations of heat and mass flows with the selection of melt chemistries in the design of future high temperature industrial reactors.     

Thermodynamic assessment of the Zinc-Rich part of the Cr-Zn system

The Cr-Zn binary system was critically assessed with the CALPHAD technique using the PARROT module of the Thermo-Calc software by taking into account new experimental measurements. The solution phases [liquid, body-centered cubic (bcc), close-packed hexagonal (cph)] were modeled with the Redlich-Kister equation. The intermetallic compounds CrZn₁₃ and CrZn₁₇ are treated as stoichiometric compounds. The experimental chromium solubilities at various temperatures modify the shape of the liquidus curve and are satisfactory for industrial applications. A set of parameters consistent with most of the available experimental data on both phase diagram and solubility measurements was obtained by optimization. A comparison with previous work is also presented.     

Computational thermodynamic model for the Mg−Al−Y system

The ternary Mg−Al−Y system was thermodynamically modeled based on the optimization of the binary subsystems Mg−Al, Mg−Y, and Al−Y using the CALPHAD approach. Mg−Al data was taken from the COST507 database, whereas the other two binary systems were reoptimized in this work. The liquid phase was described by a Redlich-Kister polynomial model, and the intermediate solid solutions were described by a sublattice model. Ternary interaction parameters were introduced to enable the best representation of the experimental data while considering the occurrence of the ternary compound Al₄MgY. The constructed database is used to calculate and predict thermodynamic properties, binary phase diagrams of Al−Y and Mg−Y, and liquidus projections of the ternary Mg−Al−Y. The calculated phase diagrams and the thermodynamic properties are in good agreement with the corresponding experimental data from the literature. Sixteen ternary four-phase-equilibria invariant points were predicted in the Mg−Al−Y system: seven ternary eutectic points, eight ternary quasi peritectic points, and one ternary peritectic point. Further, fifteen three-phase-equilibria in variant points were determined: eight saddle points and seven binary eutectic points.     

Thermodynamic assessment of the Zinc-Rich part of the Cr-Zn system

The Cr-Zn binary system was critically assessed with the CALPHAD technique using the PARROT module of the Thermo-Calc software by taking into account new experimental measurements. The solution phases [liquid, body-centered cubic (bcc), close-packed hexagonal (cph)] were modeled with the Redlich-Kister equation. The intermetallic compounds CrZn₁₃ and CrZn₁₇ are treated as stoichiometric compounds. The experimental chromium solubilities at various temperatures modify the shape of the liquidus curve and are satisfactory for industrial applications. A set of parameters consistent with most of the available experimental data on both phase diagram and solubility measurements was obtained by optimization. A comparison with previous work is also presented.     

Low temperature OMVPE growth of ZnSe withTertiary-butyl allyl selenide and dimethylzinc-triethylamine

The growth of high quality ZnSe by organometallic vapor phase epitaxy (OMVPE) has been investigated fortertiary-butyl allyl selenide (tBASe), combined with dimethylzinc-triethylamine (DMZn : NEt₃). Single crystalline ZnSe films were grown on GaAs at temperature as low as 350°C with a reasonable growth rate (~1 µm/h). Secondary ion mass spectrometry (SIMS) spectra show a negligible carbon incorporation in ZnSe films from tBASe even at high VI/II ratio, in contrast the carbon concentration of 10²¹ cm^-3 in ZnSe films grown from diallyl selenide (DASe)and methylallylselenide (MASe). Good surface morphology, crystalline and interface quality of ZnSe on (001) GaAs are confirmed by scanning electron microscopy, double crystal diffractometry (DCD) and Rutherford backscattering spectrometry (RBS). Photoluminescence at 10K shows sharp near-band-edge excitonic spectra.     

Influence of ultrasonic treatment on formation of primary Al3Zr in Al–0.4Zr alloy

The effect of ultrasonic treatment on the formation of primary Al₃Zr was investigated by applying ultrasound to an Al–0.4Zr alloy. Three temperature ranges were selected, i.e., 830 to 790 °C (above liquidus), 790 to 750 °C (cross liquidus) and 750 to 710 °C (below liquidus) for ultrasonication. Using the scanning electron microscopy, both the size and morphology of the primary Al₃Zr particles were examined. It was found that the size was significantly reduced and the morphology changed from large throwing-star shape to small compact tablet shape. The mechanisms for refinement of primary Al₃Zr were discussed. It is suggested that sonocrystallization theory via activation of aluminium oxide particles is responsible for the refinement of primary Al₃Zr when ultrasonic melt treatment (UST) is applied within the fully liquid state. The refinement of primary Al₃Zr particles when UST is applied in the slurry (growth stage) is due to the sonofragmentation.     

Selection of soldering temperature for ultrasonic-assisted soldering of 5056 aluminum alloy using Zn-Al system solders

The conditions for sound butt-joints of 5056 aluminum alloy containing 4.6 mass% Mg using Zn-xAl (x = 5, 13, and 38 mass%) solder at the relevant temperatures were investigated. Each solder foil was inserted between faying surfaces of 5056 aluminum rods. Ultrasonic vibration at a frequency of 19 kHz was applied to the faying surfaces through an aluminum substrate at soldering temperatures for 4 s in air. The strength of obtained solder joints was measured by tensile tests. The microstructure in the solder layer after the soldering process was evaluated with an SEM-EDX. The results of tensile tests revealed that joints soldered under the liquidus temperature of Zn-Al solders showed higher strength than joints soldered over the liquidus temperature. In the joints soldered over the solder liquidus temperature, the joint strength decreased with an increase in soldering temperature. It was caused by the formation of MgZn₂ in the solder layer due to dissolution of 5056-Al into the solder liquid during the soldering process. On the other hand, ultrasonic-assisted soldering under the solder liquidus temperature suppressed dissolution of 5056-Al and improved the joint strength by reducing the formation of MgZn₂.     

Co-reduction of Copper Smelting Slag and Nickel Laterite to Prepare Fe-Ni-Cu Alloy for Weathering Steel

In this study, a new technique was proposed for the economical and environmentally friendly recovery of valuable metals from copper smelting slag while simultaneously upgrading nickel laterite through a co-reduction followed by wet magnetic separation process. Copper slag with a high FeO content can decrease the liquidus temperature of the SiO₂-Al₂O₃-CaO-MgO system and facilitate formation of liquid phase in a co-reduction process with nickel laterite, which is beneficial for metallic particle growth. As a result, the recovery of Ni, Cu, and Fe was notably increased. A crude Fe-Ni-Cu alloy with 2.5% Ni, 1.1% Cu, and 87.9% Fe was produced, which can replace part of scrap steel, electrolytic copper, and nickel as the burden in the production of weathering steel by an electric arc furnace. The study further found that an appropriate proportion of copper slag and nickel laterite in the mixture is essential to enhance the reduction, acquire appropriate amounts of the liquid phase, and improve the growth of the metallic alloy grains. As a result, the liberation of alloy particles in the grinding process was effectively promoted and the metal recovery was increased significantly in the subsequent magnetic separation process.     

Optimum composition of blast furnace slag as deduced from liquidus data for the quaternary system CaO-MgO-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript>

On the basis of liquidus measurements in the system CaO-MgO-Al₂O₃-SiO₂ and previously published data, diagrams have been constructed at 5 pct Al₂O₃ intervals from 5 to 35 pct Al₂O₃. Liquidus temperatures and primary phase fields are shown. The optimum composition of a blast furnace slag for a given alumina content is indicated. At the optimum point, ordinary slags will be entirely liquid and will have maximum desulphurization potential and minimum viscosity. The relation of optimum composition of slags to the “plateau region” of the liquidus surface, and the application of these data on synthetic quaternary slags to actual slag compositions are discussed. Index of refraction of glasses is given as well as composition, temperature, and phase data for each mixture.     

Experimental study of ternary Pd-Zn-Se phase equilibria and Pd/ZnSe bulk diffusion

The ternary system Pd-Zn-Se was investigated at 340°C. A complete isothermal phase diagram is given, containing the formerly known ternary phase Pd₅ZnSe (τ₁) as well as a newly discovered ternary phase τ₂ of approximate composition Pd₆₂Zn₃₂Se₆. The reaction diffusion between Pd and ZnSe was investigated at 340°C with bulk diffusion couples Pd/ZnSe, annealed from 6 to 192 h, and the diffusion path is described. For the investigation x-ray powder diffraction, scanning electron microscopy, and energy dispersive x-ray analysis was used. Implications for the application of Pd as metallic contact to semiconducting ZnSe are outlined.