Liquid Miscibility Gap Research Articles

Critical Experiments and Thermodynamic Modeling of the Li2O-SiO2 System

Phase equilibria studies were performed in the Li2O-SiO2 system for heat-treated samples using Scanning Electron Microscope (SEM) and X-Ray Diffraction (XRD). The temperature of the eutectic reaction (Liq. ⇌ Li4SiO4 + Li2SiO3) was experimentally determined at 1289 K using Differential Thermal Analysis (DTA). No evidences of the Li6Si2O7 formation was found by the experimental investigation and therefore, it was not considered. Heat capacity of the Li8SiO6 phase was measured using Differential Scanning Calorimetry (DSC). Solid phases of the Li2O-SiO2 system were described as stoichiometric compounds and liquid phases by two-sublattice partially ionic liquid model. Four stoichiometric intermediate compounds were considered to be stable (Li8SiO6, Li4SiO4, Li2SiO3 and Li2Si2O5). The polymorphic transformation in Li2Si2O5 phase was accounted and the metastable liquid miscibility gap on SiO2-rich side was reproduced. The calculated phase diagram satisfactorily agrees with the experimental phase equilibria as well as calculated thermodynamic properties reproduces experimental values within uncertainty limits.

Effects of beam shaping on copper-steel interfaces in multi-material laser beam powder bed fusion

Multi-material laser beam powder bed fusion (PBF-LB) is a promising approach to meet industrial demands for multifunctional components, due to its enhanced freedom of design. Copper and stainless steel are interesting materials to be combined due to the high electrical and thermal conductivity of copper and the mechanical strength and wear resistance of steel. However, this system suffers from copper contamination cracking (CCC), a phenomenon which leads to intergranular cracking of the steel due to penetration of liquid copper. The more these materials intermix, the greater the amount of copper that can penetrate and damage the steel. Mixing is more intense when steel is below copper during printing, a situation that cannot always be avoided due to design constraints. In this sense, this research tackles the worst scenario of printing CuCrZr onto 316L and analyses the effect of beam shaping on interface quality. For the first time, a ring-mode laser was applied to multi-material PBF-LB with the goal to reduce intermixing. It was observed that using a ring-mode laser source instead of a Gaussian beam decreases mixing of the two alloys and reduces interface defects, albeit being unable to completely suppress cracking. Grain size and texture were also affected by the beam shape, with the Gaussian beam leading to formation of small equiaxed grains along 20 layers of CuCrZr, resulting in random texture. The ring-mode laser source, on the other hand, yields columnar grains and <100> texture along the build direction. Both beam shapes were observed to induce supercooling below the liquid miscibility gap in the Cu–Fe system. Besides the expected γ-Fe and ε-Cu phases, iron was also found to crystallize in a body-centered cubic (BCC) lattice structure, which is believed to happen due to Ni depletion of the steel in Cu-rich compositions, coupled to insufficient copper within the Fe-rich liquid during solidification. BCC fractions are higher for the Gaussian beam. These differences in microstructure and BCC fraction are attributed to the high intermixing of CuCrZr and 316L when applying Gaussian beams, which is around 10 times higher than with the ring-mode laser.

Effect of Liquid Miscibility Gap on Defects in Inconel 625–GRCop42 Joints through Analysis of Gradient Composition Microstructure

Joining of Cu-based dispersion-strengthened alloys to Ni-based superalloys has garnered increased attention for liquid rocket engine applications due to the high thermal conductivity of Cu-based alloys and high temperature tensile strength of Ni-based superalloys. However, such joints can suffer from cracking when joined via liquid state processes, leading to part failure. In this work, compositions of 15–95 wt.% GRCop42 are alloyed with Inconel 625 and characterized to better understand the root cause of cracking. Results indicate a lack of miscibility between Cu-deprived and Cu-rich liquids in compositions corresponding to 30–95 wt.% GRCop42. Two distinct morphologies are observed and explained by use of CALPHAD; Cu-deprived dendrites with Cu-rich interdendritic zones at 30–50 wt.% GRCop42 and Cu-deprived spheres surrounded by a Cu-rich matrix at 60–95 wt.% GRCop42. Phase analysis reveals brittle intermetallic phases precipitate in the 60–95 wt.% GRCop42 Cu-deprived region. Three cracking mechanisms are proposed herein that provide guidance on the avoidance of defects Ni-based superalloy to Cu-based dispersion strengthened alloy joints.

Calorimetric study of the enthalpy of mixing in the liquid systems Li-Zn and Li-Sn-Zn

Partial and integral molar enthalpies of mixing of binary liquid Li-Zn alloys and ternary liquid Li-Sn-Zn alloys were determined by drop calorimetry at 823 K. The binary system was investigated up to xZn = 0.85 and the integral mixing enthalpy was described with a Redlich-Kister-polynomial. Li-Zn shows an exothermic behavior and a minimum molar mixing enthalpy of about ΔHmix = -11.7 kJ⋅mol−1 at xZn = 0.6. The mixing enthalpy along nine ternary sections of Li-Sn-Zn (A: xLi/xSn ≈ 9:11, B: xLi/xSn ≈ 1:4, C: xSn/xZn ≈ 9:1, D: xSn/xZn ≈ 7:3, E: xSn/xZn ≈ 1:1, F: xLi/xZn ≈ 1:3, G: xLi/xZn ≈ 1:1, H: xLi/xZn ≈ 3:2, I: xLi/xZn ≈ 7:3) was investigated. Solid pieces of Li, Sn, and Zn respectively were dropped to the liquid binary starting alloys in the calorimeter at 823 K. The integral values at the crossing points of the various sections show excellent agreement. The course of the partial and integral enthalpy values along the sections A, D, E, F, G, H, and I indicate multiple-phase regions. The occurrence of such partially liquid and de-mixed liquid regions is discussed and compared with a calculated version of the isothermal section at 823 K which exhibits a large ternary liquid miscibility gap. The experimental ternary data allocated to the fully liquid monophasic regions was numerically fitted based on a Redlich-Kister-Muggianu polynomial for substitutional solutions including ternary interactions. In addition, a comparison with enthalpy values from the extrapolation methods based on binary data according to the Muggianu and Toop model, respectively, is shown. Both models fail to accurately reproduce the experimental values. Iso-enthalpy plots of calculated integral mixing enthalpy for stable and metastable fully homogeneous liquid alloys for the entire ternary system are shown.

High-pressure phase diagram of Bi-Ga: Polymorphism, anomalous melting curves and liquid miscibility gap

The high-pressure states of the elements can significantly impact the phase diagrams of their alloys due to polymorphism in the solid state and anomalies and slope changes in the melting curve. Here, we investigate the effect of these characteristics on a model system, the Bi-Ga system, by constructing a thermodynamic model of the high-pressure phase diagram and validating the proposed transitions by electrical resistance measurements in a ‘Paris-Edinburgh’ press. We achieve conclusive agreement between our calculated phase diagram up to 6 GPa and the measured transitions. At higher pressures, the liquid miscibility gap in this system disappears, and the phase diagram changes from a monotectic to a eutectic type at a pressure of 8 GPa. We also measured the monotectic temperature and the liquidus of Bi-rich alloy that presents anomalous behavior as a function of pressure. The present contribution demonstrates the crucial contribution of the high-pressure behavior of the elements in characterizing the challenging and complex behavior of alloys under pressure.

A dilute nematic gel produced by intramicellar segregation of two polyoxyethylene alkyl ether carboxylic acids

MotivationSurfactants like C8E8CH2COOH have such bulky headgroups that they cannot show the common sphere-to-cylinder transition, while surfactants like C18:1E2CH2COOH are mimicking lipids and form only bilayers. Mixing these two types of surfactants allows one to investigate the competition between intramicellar segregation leading to disc-like bicelles and the temperature dependent curvature constraints imposed by the mismatch between heads and tails. ExperimentsWe establish phase diagrams as a function of temperature, surfactant mole ratio, and active matter content. We locate the isotropic liquid-isotropic liquid phase separation common to all nonionic surfactant systems, as well as nematic and lamellar phases. The stability and rheology of the nematic phase is investigated. Texture determination by polarizing microscopy allows us to distinguish between the different phases. Finally, SANS and SAXS give intermicellar distances as well as micellar sizes and shapes present for different compositions in the phase diagrams. FindingsIn a defined mole ratio between the two components, intramicellar segregation wins and a viscoelastic discotic nematic phase is present at low temperature. Partial intramicellar mixing upon heating leads to disc growth and eventually to a pseudo-lamellar phase. Further heating leads to complete random mixing and an isotropic phase, showing the common liquid–liquid miscibility gap. This uncommon phase sequence, bicelles, lamellar phase, micelles, and water-poor packed micelles, is due to temperature induced mixing combined with dehydration of the headgroups. This general molecular mechanism explains also why a metastable water-poor lamellar phase quenched by cooling can be easily and reproducibly transformed into a nematic phase by gentle hand shaking at room temperature, as well as the entrapment of air bubbles of any size without encapsulation by bilayers or polymers.

Synthesis and magnetic properties of some monotectic composites containing ultra-dispersed particles of YGdTbDyHo high-entropy alloy

Recent discoveries of low-dimensional and ultra-dispersed magnetocaloric materials revealed interesting results that help to uncover some fundamental aspects related to the magnetocaloric effect. One of the promising way to obtain ultra-fine metallic nanocomposites resistant to environmental conditions is the use alloy systems showing a liquid miscibility gap. Within this study we fabricate some monotectic composites containing YGdTbDyHo high-entropy alloy and examine their structure, microstructure, thermal conductivity, magnetic and magnetocaloric properties, employing X-ray diffraction, electron microscopy, magnetometry and ab initio molecular dynamics simulations. The results reveal that the use of chromium, vanadium and their mutual alloys as a host monotectic matrix in combination with standard arc-melting enables the YGdTbDyHo high-entropy alloy to be evenly dispersed in the form of small irregularly-shaped particles (droplets or lamellae) of less than 1–2 μm in size, practically uncontaminated with the host metal in which these inclusions are distributed. The monotectic composites have increased Neel points, but reduced magnetocaloric response compared to non-dispersed as-cast YGdTbDyHo alloy. The observed tendencies in the behavior of magnetic properties of the developed monotectic alloys turned out to be similar to the micron powders and thin films based on rare-earth metals studied to date, i.e. the effects of micro- and nanostructuring in all systems are of the same nature and play a decisive role in their magnetism. The study results allow us to conclude that using immiscible metals in alloy fabrication process is effectient for dispersing rare-earth high entropy alloys and opens up new prospects in designing low-dimensional and nanoscale magnetic phases with adjustable magnetocaloric properties.

The phase split forced by salts or carbohydrates in nonaqueous systems

More than 2500 ternary systems containing binary nonaqueous solvents and a salt or carbohydrate were checked experimentally under ambient conditions to demonstrate the liquid–liquid phase split. The binary solvents consisted of one strongly polar component and another significantly less polar. Phase separation has been observed in more than 300 systems. These systems are direct analogues of the aqueous two-phase systems (ATPS) that have been extensively studied and found numerous applications. The obtained data were analyzed and some correlations were observed. Possibilities of creating the liquid–liquid miscibility gap depending on the solvents’ polarity and the solute properties were discussed. This phenomenon most often occurs with binary solvents containing a strongly polar component, such as formamide, dimethyl sulfoxide, ethane-1,2-diol, or N-methylformamide. Carbohydrates have been found to be better liquid–liquid phase split inducers than salts. Among the latter, calcium and lithium chlorides, and sodium iodide turned out to be the most effective. A strict correspondence of the decreasing probability of creating a miscibility gap by different ions with the reversed Hofmeister series was confirmed.

A framework to predict binary liquidus by combining machine learning and CALPHAD assessments

Knowledge of the liquidus is important for the design and processing of many materials. For instance, deep eutectics are important for the design of metallic glasses, and recently multi-principal element alloys have been designed based on eutectic compositions or melting temperatures extrapolated from binary liquidus data. In this study, we provide a general framework for predicting binary liquidus only from the properties of the pure elements and thermodynamic properties calculated by Miedema’s model. Our framework combines three machine learning models that are trained and evaluated on liquidus data collected from 466 CALPHAD assessments of binary phase diagrams. The first model predicts the formation of liquid miscibility gaps with a prediction accuracy of 95.3%, outperforming the empirical Mott model. The second and third models predict the equilibrium onset temperature of solidification and the critical temperature of liquid miscibility gaps, respectively. An important feature of our models is that they can give indications of the presence of congruent melting phases and eutectics. Using our framework, we predict the liquidus in 1563 binary systems not included in our CALPHAD dataset, many of which are unknown. By collecting more data, our framework will continue to grow towards better liquidus prediction.

Mutual and Thermal Diffusivities in Binary Mixtures of n-Hexane or 1-Hexanol with Krypton, R143a, or Sulfur Hexafluoride by Using Dynamic Light Scattering and Molecular Dynamics Simulations

This work reports Fick diffusion coefficients D11 in the saturated liquid phase(s) of binary mixtures of nonpolar n-hexane (n-C6H14) or polar 1-hexanol (1-C6H14O) with dissolved krypton (Kr), 1,1,1-trifluoroethane (R143a), or sulfur hexafluoride (SF6). Investigations were performed at temperatures T of 303, 323, and 348 K and gas mole fractions up to 0.999. The comparison between Kr and R143a, both having nearly the same molar mass, allows identification of the impact of molecular structure and polarity of the dissolved gas on D11. The investigation of SF6 provides information about the influence of a centrosymmetric molecule with a large molar mass on D11. D11 is experimentally determined by dynamic light scattering (DLS) and predicted by equilibrium molecular dynamics (EMD) simulations by the independent calculation of the Maxwell–Stefan diffusivity and the thermodynamic factor Γ11 in macroscopic thermodynamic equilibrium at or close to saturation conditions. Thermal diffusivity data obtained simultaneously with D11 by DLS are reported as well. The behavior of the experimentally determined D11 as a function of composition and that obtained from EMD simulations show generally good agreement. Distinct structural changes of the saturated liquid phase are reflected by the change of Γ11 which extends for the present study between 0.16 and 1.3. While for mixtures of 1-C6H14O + Kr, D11 as a function of composition is nearly constant at a given T, all other mixtures show a distinct composition-dependent behavior. For mixtures of 1-C6H14O + R143a and 1-C6H14O + SF6, a strong slowing down of D11 was observed and related to approaching a liquid–liquid miscibility gap. For all systems, the behavior of D11 as a function of composition is interpreted with reference to the fluid structure accessible by EMD.

Thermodynamic modeling of the Fe-Sn system including an experimental re-assessment of the liquid miscibility gap

The usage of low-grade ferrous scrap has increased over decades to decrease CO2 emissions and to produce steel products at a low cost. A serious problem in melting post-consumer scrap material is the accumulation of tramp elements, e.g., Cu and Sn, in the liquid steel. These tramp elements are difficult to remove during conventional steelmaking processes. Sn is considered as one of the most harmful tramp elements because, together with Cu, it sometimes induces the liquid metal embrittlement in high-temperature ferrous processing, e.g., continuous casting and hot rolling. Furthermore, the chemical interaction between Fe and Sn plays an important role in the Sn smelting process. The raw material used in the Sn smelting process is SnO2 (cassiterite), in which Fe3O4 is a gangue in the Sn ore. In the process, the reduction of Fe3O4 is unavoidable, which results in forming a Fe-Sn alloy (hardhead). The recirculation of the hardhead decreases the furnace capacity and increases the energy consumption in the smelting. The need to efficiently recover Sn from secondary resources is therefore inevitable. The CALculation of PHAse Diagrams (CALPHAD) approach helps to predict the equilibrium state of the multicomponent system. Previously reported studies of the Fe-Sn system show inconsistencies in the calculations and the experimental results. Mainly the miscibility gap in the liquid phase was under debate, as experimental data of the phase boundary are scattered. Experimental study and re-optimization of model parameters were carried out with emphasis on the correct shape of the miscibility gap. Three different experimental techniques were employed: differential scanning calorimetry, electromagnetic levitation, and contact angle measurement. The present thermodynamic model has higher accuracy in predicting the solubility of Sn in the body-centered cubic (bcc), compared to previous assessments. This is achieved by re-evaluating the Gibbs energies of the FeSn and FeSn2 compounds and the peritectic reaction related to Fe5Sn3. Also, the inconsistencies related to the miscibility gap around XSn = 0.31-0.81 were resolved. The database developed in the present study can contribute to the development of a large CALPHAD database containing tramp elements.

Problems in Imaging the Decomposition of Liquid and Solid Solutions in the Ag–Cu–Ni and Ag–Cu–Pb Systems

Three-dimensional (3D) computer models of Ag–Cu–Ni and Ag–Cu–Pb isobaric phase diagrams, designed based on 23 and 31 base points, respectively, assembled from 14 and 32 surfaces, 9 and 15 phase fields, respectively, and intended to digitize information on these diagrams, are used to verify the adequacy of interpretation of published isothermal and polythermal sections, both calculated and experimentally studied ones. The geometric features of the phase diagram regions that relate to liquid–liquid miscibility gaps and solid solution decomposition are refined in the 3D models. Mistakes arising from an incorrect imaging of the decay of copper–nickel solid solutions and from discrepancies in the values of the Ag–Cu–Pb ternary eutectic temperature are shown on polythermal sections.

A lumped parameter model of continuous/dispersed phases mass transfer for simulating in-vessel corium stratification transients

In the frame of in-vessel corium modelling, this paper proposes an enhanced integral model in order to simulate the liquid phases stratification transients associated with the miscibility gap in the O,U,Zr,steel system. An important feature of this model is that it explicitly takes into account mono-dispersed metal phases in the continuous oxide phase. These droplets can either come from a direct molten steel relocation or be detached by Rayleigh–Taylor instabilities at the interface between the heavy or light metal layers and the oxide layer of the stratified pool. At all interfaces between metal and oxide phases, a same consistent local equilibrium assumption (based on a same simplified thermodynamic representation of the liquid miscibility gap) is made.A limited parametric analysis is reported. It highlights the possible impact of direct molten steel relocation into the oxide phase in comparison with a relocation on the top of the pool. Indeed, the U,Zr enrichment of the metal droplets during their residence time in the oxide phase significantly affects the remainder of the stratification transients in all cases. The parameters that affect this mass transfer are shown to have a significant impact on the overall stratification kinetics. These results also highlight an important qualitative difference between the two kinds of stratification transients: heavy metal phase formation or stratification inversion. In the latter, the heavy metal phase average composition always stays close to its interface composition equilibrium with the oxide and, accordingly, when the density criterion associated with the Rayleigh–Taylor instability is met, the heavy metal layer is, in most cases, completely relocated at the top of the pool. During the heavy metal phase formation, the situation is drastically different as the light metal layer is not initially close to equilibrium with the oxide in such a way that several intermittent droplets detachment are predicted.These different trends are reported taking into account the model underlying hypotheses and the path to move forward and increase knowledge about stratification kinetics is discussed.

Thermodynamic analysis for solidification path of simulated ex-vessel corium

Molten corium is considered to form in a severe accident at the Fukushima Daiichi Nuclear Power Station (FDNPS). Investigation of the primary containment vessel (PCV) inside the FDNPS showed that a significant amount of the molten corium reached the bottom of the pedestal region. The molten corium and concrete likely caused a complex interaction called Molten Corium Concrete Interaction (MCCI). Then, ex-vessel debris was formed after the solidification of the MCCI products and accumulated in the pedestal region. The solidification hysteresis of ex-vessel debris significantly influences its properties. We performed a thermodynamic analysis using the TAF-ID database to infer the solidification path of U–Zr–Al–Ca–Si–O molten corium, which was chosen for a prototypic system of ex-vessel debris. The solidification path for the CaO-rich sim-corium showed the following sequence: (i) melting as a single liquid phase at temperatures higher than 2430 K, (ii) selective solidification of the oxide-rich corium mainly consisted of fuel materials, and (iii) solidification of the remaining materials as a silicate matrix. In contrast, the solidification path for the SiO2-rich corium indicated that (i) formation of liquid miscibility gap above 2200 K between U-rich and Zr-rich oxidic melts, (ii) individual precipitation of solid phases in each liquid phase. Identified features of these solidification paths were in good agreement with the experimental data for the solidified sim-corium.

Butler‐based thermodynamic modeling of interfacial energies for in‐vessel corium systems

The modeling of transient phase segregation phenomena in corium multicomponent thermodynamic systems is complicated especially in the liquid miscibility gap which can lead to phase separation (stratification of the liquid phases for corium) and is of tremendous importance. The modeling of the associated phase separation transients in corium stratification is limited by a deficiency in the interfacial energy data, which are difficult to measure experimentally for these high-temperature systems. The limitations of summarizing the interfacial energies as constant coefficients were observed in a recent work on simulation of the stratification kinetics of a corium pool and the necessity to improve the estimation of interfacial energies [1,2]. This work tests the efficacy of a thermodynamic approach to evaluate the interfacial tensions, initially proposed for metallic systems by Kaptay [3]. This method is based on the Butler equation and makes use of existing thermodynamic databases for multicomponent systems constructed by the CALPHAD method. In practice, the application of this method to corium systems was performed using the open-source code openIEC [4]. To do so, this code was modified to enable required features, both functionally and methodically. In particular, the OpenCalphad Gibbs energy minimizer has been interfaced in this framework and benchmarked against previous results. Then, interfacial energies were calculated for two relevant corium systems (U-O and U-O-Zr-Fe) using two different existing databases (TAF-ID and NUCLEA). The first results obtained were analyzed in terms of general trends and compared to existing theoretical aspects. Large differences were observed depending on the thermodynamic database that was used.

Liquid–liquid equilibria in mixtures of formaldehyde, water, methanol, and isoprenol

Isoprenol (3-methyl-3-buten-1-ol) is an important intermediate in the chemical industry. It has to be separated from mixtures containing formaldehyde, water, and methanol in the production process. As water and isoprenol are only partially miscible in the liquid phase, these mixtures exhibit a liquid–liquid miscibility gap. Knowledge of this miscibility gap is essential for understanding the isoprenol process; however, only few experimental data and no models are presently available in the literature. Therefore, in the present work, liquid–liquid equilibria in the systems (water + isoprenol), (formaldehyde + water + isoprenol), and (water + methanol + isoprenol) were measured at 278, 293, and 313 K. The new experimental data were used to develop a model of the liquid–liquid equilibrium in mixtures of formaldehyde, water, methanol, and isoprenol, which can now be used in simulation studies of the isoprenol process.

Thermodynamic assessment of the miscibility gaps and the metastable liquidi in the Zn‐Bi, Zn‐Pb, and Zn‐Tl systems

Abstract In monotectic systems, there are thermodynamic restrictions on compositions and temperatures below the monotectic where the equilibrium solid cannot form directly from the undercooled homogeneous liquid. In this region, the solid can form only after liquid – liquid phase separation has occurred. As suggested by earlier research, the thermodynamic restrictions on the solidification process may be useful to control the microstructure of rapidly solidified materials. Thus, it could be commercially important to understand the thermodynamic limitations on the formation of the solid in monotectic systems. The liquid miscibility gaps, metastable liquidi, and spinodal curves in the binary Zn– Bi, Zn–Pb, and Zn–Tl systems were assessed by using a subregular solution model to describe the Gibbs energies of the liquid phases. The present results were compared and discussed with other experimental and assessed data available in the literature.

Examination of the binary system Al2O3‐ZrO2 by aero acoustic levitation melting

AbstractAl2O3‐ZrO2 composites exhibit excellent mechanical and high‐temperature properties. The solidification of various hypoeutectic compositions has been studied by means of aero‐acoustic levitation. A high‐speed camera recorded the crystallization, to the correlation of the video stills with the observed microstructures. Solidification takes place by formation of several nuclei and subsequent growth. Nuclei are formed in the supercooled melt, entailing to a fine‐grained, simultaneously solidified structure. The remaining melt between the growing nuclei is heated due to recalescence leading to primary precipitation of zirconia, followed by eutectic solidification. A consistent behavior is presented to explain the observed microstructures. Additionally, samples between 40 and 50 mol% ZrO2 exhibit lamellar areas, which exceed the initial zirconia composition. The observed microstructure strongly indicates the existence of a liquid miscibility gap.

Experimental study of “CuO0.5”-“FeO”-SiO2 and “FeO”-SiO2 systems in equilibrium with metal at 1400–1680 °C

The phase equilibria of the “CuO0.5”-“FeO”-SiO2 slag system in equilibrium with metallic copper and tridymite/cristobalite (SiO2), and the “FeO”-SiO2 slag system in equilibrium with metallic iron and tridymite/cristobalite (SiO2) were investigated between 1400 and 1680 °C. High temperature equilibration in closed silica ampoules, followed by quenching and the direct measurement of the phase compositions with the electron probe X-ray microanalysis (EPMA) was used. The liquidus isotherms in the tridymite and cristobalite (SiO2) primary phase fields were measured, and the shape of the two liquid slags miscibility gap over cristobalite was determined for the “CuO0.5”-“FeO”-SiO2 and “FeO”-SiO2 systems in equilibrium with metallic copper and iron respectively. The two liquid slags miscibility gap over cristobalite was found to be present at all Cu/(Cu+Fe) molar ratios in the slag. However, the difference in the SiO2 concentration between the low- and high-SiO2 slag was found to decrease as the Cu/(Cu+Fe) molar ratio in slag approached 0.5, with the minimal difference assessed to be approximately 4 mol.%. Additionally, new phase equilibria data obtained for the “FeO”-SiO2 subsystem in equilibrium with metallic iron suggested that the monotectic temperature of the subsystem is 1673 ± 3 °C, and that the low- and high- SiO2 slags contain 59.7 mol.% and 96.4 mol.% SiO2 respectively. The present study was a continuation of previous investigations by the authors into the Cu-Fe-Si-O multicomponent slag system, aimed at providing information for improving the thermodynamic models for all phases in this system.

Thermodynamic re-assessment and liquidus projection of the Cu–Ni–Ti system

A critical thermodynamic re-assessment for the ternary Cu–Ni–Ti system was performed by means of the CALPHAD (CALculation of PHAse Diagram) approach, and a new set of self-consistent thermodynamic parameters for the Cu–Ni–Ti system was obtained. According to the reported crystal structures and homogeneity ranges, appropriate sublattice models were proposed for the τ4 and τ6 phases, which could achieve a better description than the previous stoichiometric compound model for phase compositions and primary phase regions. Three solid-state invariant reactions, CuTi + τ1 ↔ Cu4Ti3 + NiTi at 1074.86 K, Ni3Ti + NiTi + τ1 ↔ τ2 at 1074.39 K and NiTi + τ4 ↔ Ni3Ti + τ1 at 1175.11 K were predicted in the present work. Presently calculated liquidus projection eliminated the liquid miscibility gap of the Cu–Ni–Ti system on Cu–Ni side. Scheil reaction scheme of the entire composition range was also presented accordingly. Comparisons between the calculated results and the measured phase equilibria indicated that all the reliable experimental data were satisfactorily accounted for by the present modeling.