Thermodynamic Solution Model Research Articles

Sorption of Se(VI) and Se(IV) on AFm phases

Selenate and selenite can sorb on AFm phases such as monosulfate, monocarbonate or hemicarbonate. Sorption and co-precipitation experiments were performed to determine their potential for the immobilization of two of the main aqueous species of selenium: SeVIO42− and SeIVO32−. A preferential uptake by hemicarbonate over monosulfate, and a much weaker sorption on monocarbonate was observed for both Se(IV) and Se(VI). Increased sulfate and carbonate concentrations as present at higher pH lowered the uptake of Se(VI) and Se(IV).Experimentally obtained sorption isotherms on hemicarbonate and monosulfate were reproduced with thermodynamic solid solution models, considering both surface sorption and interlayer bonding. For monocarbonate interlayer sorption was suppressed by the rigid structure and narrow interlayer distance. The observed limited uptake could be described by an anion exchange model on the outer surfaces only. This study shows that both anion exchange in the interlayer as well as sorption on outer surface sites can determine Se uptake by AFm phases.

Evaluation and thermodynamic optimization of phase diagram of lithium niobate tantalate solid solutions

The lithium niobate–lithium tantalate solid solution’s phase diagram was investigated using experimental data from differential thermal analysis (DTA) and crystal growth. We used XRF analysis to determine the elemental composition of the crystals. The Neumann–Kopp rule provided essential data for the end members lithium niobate (LN) and lithium tantalate (LT). The heats of fusion of the end members, given by DTA measurements, are 103 kJ/mol at 1531 K for LN and 289 kJ/mol at 1913 K for LT. These values were used as input parameters to generate the data. This data served as the basis for calculating a phase diagram for LN-LT solid solutions. Finally, based on the experimental data and a thermodynamic solution model, the Calphad Factsage module optimized the phase diagram. We also generated thermodynamic parameters for Gibbs’ excess energy of the solid solution. A plot of the segregation coefficient as a function of Ta concentration was derived from the phase diagram.

Integrated Experimental Phase Equilibria and Thermodynamic Modelling Research and Implementation in support of progress of process pyrometallurgy towards sustainability

Responding to the many sustainability challenges facing the metallurgical industry, we report progress that has been made on the development of predictive tools that can be applied to a wide range of technologies. The aim is to provide accurate, fundamentally-based thermodynamic tools that can be used by industry to improve process efficiencies, metal recoveries and productivities, and reduce energy requirements of pyrometallurgical systems. The program involves an integrated experimental and thermodynamic modelling research on phase equilibria in complex multi-component, multi-phase gas-slag-matte-speiss-metal-solids system with the Cu2O-PbO-ZnO-FeO-Fe2O3-CaO-Al2O3-MgO-SiO2-S major and As-Sn-Sb-Bi-Ag-Au-Ni-Co-Cr-Na minor elements. The experiments involve high temperature equilibration in controlled gas atmospheres, rapid quenching and direct measurement of equilibrium phase compositions with quantitative microanalytical techniques, including electron probe X-ray microanalysis and Laser Ablation ICP-MS. The thermodynamic modelling is undertaken using FactSage software package with advanced thermodynamic solution models. The continuing development of analytical and research methodologies has resulted in significant advances in predictive capability. Implementation of the results of fundamental studies involves ongoing collaboration of researchers and industry technologists, and the provision of advanced professional training. An overview of recent progress in research, implementation and applications in industrial practice will be presented in the paper.

A Fast and Robust Method for Predicting the Phase Stability of Refractory Complex Concentrated Alloys using Pairwise Mixing Enthalpy

The ability to predict the composition- and temperature-dependent stability of refractory complex concentrated alloys (RCCAs) is vital to the design of high-temperature structural alloys. Here, we present a model based on first-principles calculations to predict the thermodynamic stability of multicomponent equimolar solid solutions in a high-throughput manner and apply it to screen over 20,000 compositions. We develop a database that contains pairwise mixing enthalpy of 17 refractory metals using density-functional theory (DFT)-based total energy calculations. To these, we fit thermodynamic solution models that can accurately capture the mixing enthalpy of multicomponent BCC solid solutions. By comparing their energy with DFT-calculated enthalpy of intermetallics from the Materials Project database and using convex hull analyses, we identify the stable phase of any RCCA as a function of temperature. The predicted stability of NbTiZr, NbTiZrV, and NbTiZrVM(M= Mo,Ta,Cr) systems as a function of temperature agree well with prior experimental observations. We apply our model to predict the phase evolution in NbVZr-Tix (0 < x < 1), which is confirmed experimentally using a high-throughput, laser deposition-based synthesis technique. This method provides a fast and accurate way to estimate the phase stability of new RCCAs to expedite their experimental discovery.

WISTFUL: Whole‐Rock Interpretative Seismic Toolbox for Ultramafic Lithologies

AbstractTo quantitatively convert upper mantle seismic wave speeds measured into temperature, density, composition, and corresponding and uncertainty, we introduce the Whole‐rock Interpretative Seismic Toolbox For Ultramafic Lithologies (WISTFUL). WISTFUL is underpinned by a database of 4,485 ultramafic whole‐rock compositions, their calculated mineral modes, elastic moduli, and seismic wave speeds over a range of pressure (P) and temperature (T) (P = 0.5–6 GPa, T = 200–1,600°C) using the Gibbs free energy minimization routine Perple_X. These data are interpreted with a toolbox of MATLAB® functions, scripts, and three general user interfaces: WISTFUL_relations, which plots relationships between calculated parameters and/or composition; WISTFUL_geotherms, which calculates seismic wave speeds along geotherms; and WISTFUL_inversion, which inverts seismic wave speeds for best‐fit temperature, composition, and density. To evaluate our methodology and quantify the forward calculation error, we estimate two dominant sources of uncertainty: (a) the predicted mineral modes and compositions, and (b) the elastic properties and mixing equations. To constrain the first source of uncertainty, we compiled 122 well‐studied ultramafic xenoliths with known whole‐rock compositions, mineral modes, and estimated P‐T conditions. We compared the observed mineral modes with modes predicted using five different thermodynamic solid solution models. The Holland et al. (2018, https://doi.org/10.1093/petrology/egy048) solution models best reproduce phase assemblages (∼12 vol. % phase root‐mean‐square error [RMSE]) and estimated wave speeds. To assess the second source of uncertainty, we compared wave speed measurements of 40 ultramafic rocks with calculated wave speeds, finding excellent agreement (Vp RMSE = 0.11 km/s). WISTFUL easily analyzes seismic datasets, integrates into modeling, and acts as an educational tool.

Equilibrium phase diagrams of isostructural and heterostructural two-dimensional alloys from first principles

SummaryAlloying is a successful strategy for tuning the phases and properties of two-dimensional (2D) transition metal dichalcogenides (TMDCs). To accelerate the synthesis of TMDC alloys, we present a method for generating temperature-composition equilibrium phase diagrams by combining first-principles total-energy calculations with thermodynamic solution models. This method is applied to three representative 2D TMDC alloys: an isostructural alloy, MoS2(1-x)Te2x, and two heterostructural alloys, Mo1-xWxTe2 and WS2(1-x)Te2x. Using density-functional theory and special quasi-random structures, we show that the mixing enthalpy of these binary alloys can be reliably represented using a sub-regular solution model fitted to the total energies of relatively few compositions. The cubic sub-regular solution model captures 3-body effects that are important in TMDC alloys. By comparing phase diagrams generated with this method to those calculated with previous methods, we demonstrate that this method can be used to rapidly design phase diagrams of TMDC alloys and related 2D materials.

A Fast and Robust Method for Predicting the Phase Stability of Refractory Complex Concentrated Alloys Using Pairwise Mixing Enthalpy

The ability to predict the composition- and temperature-dependent stability of refractory complex concentrated alloys (RCCAs) is vital to the design of high-temperature structural alloys. Here, we present a model based on first-principles calculations to predict the thermodynamic stability of multicomponent equimolar solid solutions in a high-throughput manner and apply it to screen over 20,000 compositions. We develop a database that contains pairwise mixing enthalpy of 17 refractory metals using density-functional theory (DFT)-based total energy calculations. To these, we fit thermodynamic solution models that can accurately capture the mixing enthalpy of multicomponent BCC solid solutions. By comparing their energy with DFT-calculated enthalpy of intermetallics from the Materials Project database and using convex hull analyses, we identify the stable phase of any RCCA as a function of temperature. The predicted stability of NbTiZr, NbTiZrV, and NbTiZrVM (M = Mo,Ta,Cr) systems as a function of temperature agree well with prior experimental observations. We apply our model to predict the phase evolution in NbVZr-Tix (0 < x < 1), which is confirmed experimentally using a high-throughput, laser deposition-based synthesis technique. This method provides a fast and accurate way to estimate the phase stability of new RCCAs to expedite their experimental discovery.

Geophysical and cosmochemical evidence for a volatile-rich Mars

Constraints on the composition of Mars principally derive from chemical analyses of a set of Martian meteorites that rely either on determinations of their refractory element abundances or isotopic compositions. Both approaches, however, lead to models of Mars that are unable to self-consistently explain major element chemistry and match its observed geophysical properties, unless ad hoc adjustments to key parameters, namely, bulk Fe/Si ratio, core composition, and/or core size are made. Here, we combine geophysical observations, including high-quality seismic data acquired with the InSight mission, with a cosmochemical model to constrain the composition of Mars. We find that the FeO content of Mars' mantle is 13.7±0.4 wt%, corresponding to a Mg# of 0.81±0.01. Because of the lower FeO content of the mantle, compared with previous estimates, we obtain a higher mean core density of 6150±46 kg/m3 than predicted by recent seismic observations, yet our estimate for the core radius remains consistent around 1840±10 km, corresponding to a core mass fraction of 0.250±0.005. Relying on cosmochemical constraints, volatile element behaviour, and planetary building blocks that match geophysical and isotopic signatures of Martian meteorites, we find that the liquid core is made up of 88.4±3.9 wt% Fe-Ni-Co with light elements making up the rest. To match the mean core density constraint, we predict, based on experimentally-determined thermodynamic solution models, a light element abundance in the range of ≈9 wt% S, ⩾3 wt% C, ⩽2.5 wt% O, and ⩽0.5 wt% H, supporting the notion of a volatile-rich Mars. To accumulate sufficient amounts of these volatile elements, Mars must have formed before the nebular gas dispersed and/or, relative to Earth, accreted a higher proportion of planetesimals from the outer protoplanetary disk where volatiles condensed more readily.

Extensions of CASH+ thermodynamic solid solution model for the uptake of alkali metals and alkaline earth metals in C-S-H

The new CASH+ core sublattice solid solution model of calcium-silicate-hydrate (C-S-H) can describe calcium uptake, solubility, water content, and mean silicate chain length up to 90 °C. In this study, the model has been consistently extended to describe the equilibrium uptake of alkalis (Li, Na, K, Rb, Cs) and alkaline earths (Mg, Sr, Ba, Ra). The new endmembers for each cation were defined, and their properties, along with binary interaction parameters, were fitted against known aqueous and solid phase compositions. The CASH+ model with its extensions can be directly used in GEMS codes or discretized and exported for use with other geochemical speciation computer programs. In agreement with the experimental data, the model indicates that the uptake of alkalis and alkaline earth cations occurs mainly as a competitive (interlayer) ion exchange, uptake is favored at low C/S ratios, silicate chains get shorter at higher pH, and the uptake of bivalent cations (in the order Mg2+ < Ca2+ < Sr2+ < Ba2+ < Ra2+) is preferential over that of monovalent cations (Li+ ≈ Na+ < K+ ≈ Rb+ ≈ Cs+).

Mechanisms and thermodynamic modelling of iodide sorption on AFm phases

Both, experimental and modelling evidence is presented in this study showing that interlayer anion exchange is the dominant sorption mechanism for iodide (I-) on AFm phases. AFm phases are Ca-Al(Fe) based layered double hydroxides (LDH) known for their large potential for the immobilization of anionic radionuclides, such as dose-relevant iodine-129, emanating from low- and intermediate-level radioactive waste (L/ILW) repositories. Monosulfate, sulfide-AFm, hemicarbonate and monocarbonate are safety-relevant AFm phases, expected to be present in the cementitious near-field of such repositories. Their ability to bind I- was investigated in a series of sorption and co-precipitation experiments. The sorption of I- on different AFm phases was found to depend on the type of the interlayer anion. Sorption Rd values are very similar for monosulfate, sulfide-AFm and hemicarbonate. A slightly higher uptake occurs by AFm phases with a singly charged anion in the interlayer (HS-AFm) as compared to AFm with divalent ions (monosulfate), whereas uptake by hemicarbonate is intermediate. No significant sorption occurs onto monocarbonate. Our derived thermodynamic solid solution models reproduce the experimentally obtained sorption isotherms on HS-AFm, hemicarbonate and monosulfate, indicating that anion exchange in the interlayer is the dominant mechanism and that the contribution of I- electrostatic surface sorption to the overall uptake is negligible.

Thermodynamic Effect of NaCl and KCl Addition on the Equilibrium Between Molten ZnCl2-Based Salt and Liquid Zn–Cd Alloy

Purification of molten salt is essential for producing highly pure metal from melts by chemical reactions and electrolysis. Cementation is a technique used for refining molten ZnCl2-based salt. In this study, we investigated the thermodynamics involved in the reduction of CdCl2 in molten ZnCl2-based salt with Zn metal to optimize the separation conditions for Cd; this is difficult as both Cd and Zn have similar electrochemical potentials. We experimentally investigated the thermodynamic equilibrium between the molten ZnCl2-based salt and liquid Zn–Cd alloy at 723 K (450 °C). The equilibrium concentration of CdCl2 in 40 mol pct ZnCl2-NaCl-KCl coexisting with Zn-Cd alloy changed as the ratio of NaCl and KCl was altered. The activity coefficient of CdCl2 in the system at 723 K (450 °C) was obtained with the calculated activity coefficient of ZnCl2 using several thermodynamic solution models. A two-step cementation process was used to demonstrate the possibility of lowering the concentration of Cd. The Cd content in molten salt was lowered to ~ 10 mass ppm by the two-step reaction, and the feasibility of multi-step cementation was demonstrated.

Kinetic Modeling of Nonmetallic Inclusions Behavior in Molten Steel: A Review

The kinetic modeling for the nucleation, size growth, and compositional evolution of nonmetallic inclusions in steel was extensively reviewed in the present article. The nucleation and initial growth of inclusion in molten steel during deoxidation as well as the collision growth, motion, removal, and entrapment of inclusions in the molten steel in continuous casting (CC) tundish and strand were discussed. Moreover, the recent studies on the prediction of inclusion composition in CC semiproducts were introduced. Since the 1990s, the development of thermodynamic model and relevant databases for inclusion engineering has been initiated by the steel industry. Later, the commercial software FACTSAGE employing the FACT database was widely used to predict the gas (atmosphere/bubble)–liquid (steel/slag/inclusion)–solid (refractory/slag/steel/inclusion) multiphase equilibria. With the help of the comprehensive thermodynamic database and solution models in conjunction with the development of user-friendly computing packages, the kinetics of inclusion evolution in molten steel can be successfully predicted based on several kinetic models such as the coupled reaction (CR) model, reaction zone model, and tank series recirculation (TSR) model. However, some parameters are needed to represent the real processes according to the model employed at different operational or experimental conditions. The effect of reoxidation on the evolution of inclusions in the ladle and tundish, which was experimentally confirmed, can be simulated by the effective equilibrium reaction zone (EERZ) model. The complex slag–steel interfacial reaction phenomena have been successfully explained by the interfacial kinetic model based on the dynamic interfacial tension and oxygen adsorption/desorption characteristics at the slag-steel interface.

Stacking Fault Energy Based Alloy Screening for Hydrogen Compatibility

The selection of austenitic stainless steels for hydrogen service is challenging since there are few intrinsic metrics that relate alloy composition to hydrogen degradation. One such metric, presented here, is intrinsic stacking fault energy (SFE). This work reviews the exiting literature to use estimated intrinsic SFE values, calculated with a sub-regular solution thermodynamic model, to compare the retention of tensile ductility of γ-austenitic stainless steels in the presence of hydrogen. The goal is to demonstrate SFE as a metric to screen γ-austenitic stainless steels that use diverse alloying strategies for hydrogen compatibility. A transition in the tensile reduction of area of both 300-series and manganese-stabilized stainless steels is observed at a calculated stacking fault energy of approximately 39 mJ m−2, below which pronounced hydrogen degradation on tensile ductility is observed. Calculated intrinsic stacking fault energy is demonstrated as a high-throughput screening metric for a diverse range of austenitic stainless steel compositions with regard to hydrogen compatibility.

Relevance of the thermodynamic ERAS model for liquid mixtures with components exhibiting a small degree of self-association

The thermodynamic extended real associated solution (ERAS) model is reviewed and modified to accommodate weakly associating components. ERAS is a theoretical scheme applied to binary liquid mixtures whereby certain physically meaningful parameters such as the association equilibrium constants, species reduced volume and energy terms may be determined by optimization against the experimental excess molar volumes and enthalpies. The implicit assumption used for any non-associating molecule B is to routinely set the hydrogen-bonding energy ΔhB*, reaction volume ΔvB* and association constants KB to zero. It is proven here that such assignments lead to singularities in the ERAS parameters that are featured in the excess state functions used. A series of optimizations using the results of conductor-like screening model for real solvents (COSMO-RS) on the excess enthalpy HE of dimethoxymethane in binary mixtures with a series of alcohols are determined, and the parameters ΔhB*, ΔhAB* (mixed enthalpy of reaction) and XAB (interaction parameter) are determined. It is shown that the stipulated range of XAB values from ERAS theory requires minor modification if the above assumptions are not made. The magnitude of the computed variables are shown to be physically reasonable. The Bondi group averaged estimates for si, the ratio of the van der Waals (vdW) surface area to the vdW volume for molecule i, are contrasted against the more specific and reliable derivations from quantum calculations when calculating the excess functions. The degree of correlation is improved using the latter si values. We conclude that the results of the optimizations indicate that the ERAS model can be extended even to weakly self-associating components previously considered impossible in especially engineering thermodynamical applications, with the above modifications and refinements.

Stacking Fault Energy Maps of Fe–Mn–Al–C–Si Steels: Effect of Temperature, Grain Size, and Variations in Compositions

A subregular solution thermodynamic model was employed to calculate the stacking fault energy (SFE) in Fe–Mn–Al–C–Si steels with contents of carbon 0.2–1.6 wt.%, manganese 1–35 wt.%, aluminum 1–10 wt.%, and silicon 0.5–4 wt.%. Based on these calculations, temperature-dependent and composition-dependent diagrams were developed in the mentioned composition range. Also, the effect of the austenite grain size (from 1 to 300 μm) on SFEs was analyzed. Furthermore, some results of SFE obtained with this model were compared with the experimental results reported in the literature. In summary, the present model introduces new changes that shows a better correlation with the experimental results and also allows to expand the ranges of temperatures, compositions, grain sizes, and also the SFE maps available in the literature to support the design of Fe–Mn–Al–C–Si steels as a function of the SFE.

Application of a simple subregular solution model to the computation of phase boundaries and free dendritic growth in the Ag-Cu system

Adopting of a simple, but dependable analytic thermodynamic solution model in the simulation of phase transformation kinetics reduces the complexity of computation and the need for extensive thermodynamic data and hence is desired in the practical application of kinetic theories in materials processing. A simple subregular solution model with linear temperature dependency, which can calculate G curves with limited information extracted from an equilibrium phase diagram, is presented and applied to the calculation of (1) the binary Ag-Cu phase diagram with metastable phase boundaries and (2) the kinetics of free dendritic growth in supercooled Ag-Cu melts. The simple T-dependent subregular solution model can duplicate the published Ag-Cu phase diagram with the predicted metastable extensions to the same accuracy as that of calculations with highly structured models that require more computation and wider range of thermodynamic data. Its integration with a free dendritic growth model permits the calculation of correct values of the driving force at non-Henrian interfacial solute concentrations that occur in rapid solidification. The use of the simple T-dependent subregular solution model to calculate the interfacial driving force greatly improves the mathematical stability in the transition stage from mass transfer-limited growth to heat transfer-limited crystal growth.

Shooting at a moving target: phase equilibria modelling of high‐temperature metamorphism

AbstractThermodynamic modelling and calculation of P–T pseudosections are commonly employed for quantifying the P–T evolution of metamorphic rocks. A key assumption involved in interpreting a P–T pseudosection is that the bulk‐rock composition used is representative of the effective bulk composition (EBC) from which apparently equilibrated mineral assemblages grew. Choosing an EBC can be difficult in cases where the rock has evolved significantly throughout the P–T history and has become domainal for whatever reason (e.g. loss of fluid and/or melt), particularly at suprasolidus conditions. During partial melting, melt migration may not only change the bulk composition by melt loss but also may generate local variations due to the variable consumption/loss of melt from domain to domain to create volumes of rock that were once internally equilibrated in the presence of a grain boundary melt, but which departed from equilibrium as inter‐granular mobility was slowed by local reductions in melt volume. As well as careful consideration of an EBC, the results of thermodynamic modelling are highly dependent on the specific thermodynamic data set and solution models used, as updates to these data sets may lead to substantially different calculated phase equilibria. This contribution addresses: (1) how consideration of evolving EBCs at multiple scales of observation can be used to resolve the history of complex high‐grade rocks, and (2) how use of different thermodynamic data sets and a–x models (i.e. thermocalc ds5.5 v. ds6) can result in different interpretations of metamorphic evolution. This study investigates the evolution of a mineralogically heterogeneous and texturally complex hand sample of granulite from the Gruf Complex (Central Alps). At the hand‐specimen scale, an EBC can be identified and used to constrain the P–T conditions at which the ‘whole rock’ was last in mutual equilibrium, in the presence of intergranular melt that has subsequently been lost or consumed. Smaller macrodomains (~cm scale) and microdomains (~mm scale) can be identified that represent subsequent evolution during and after melt channelization and loss, and P–T pseudosections can be calculated for the compositions of these domains. Using this approach reveals that the sample experienced a clockwise P–T path marked by near‐isothermal decompression following attainment of peak UHT conditions (~960 °C, 8.5 kbar). The approach enables construction of a P–T history of a rock for which P–T pseudosections are otherwise difficult to interpret. Thermodynamic modelling using ds6 yields similar results to those stated above, but suggests: (1) near‐isothermal decompression occurred over a wider pressure range (~0.5 kbar v. 1.5 kbar), and (2) that not all microdomains record this part of the P–T evolution.

Study of wetting on chemically soften interfaces by using combined solution thermodynamics and DFT calculations: forecasting effective softening elements.

Despite recent progress in understanding the wetting principles on soft solids, the roles of chemical bonding in the formation of interfaces have been largely ignored, because most of these studies are conducted at room temperatures. Here we propose a universal wetting principle from solution thermodynamics to account for the softening of both the solid and liquid surfaces (stable or metastable). Density functional theory (DFT) calculations are applied to evaluate the stability and electron transportation across the interfaces. We find that wetting is dominated by the system entropy changes involving not only the stable liquid alloy phase but also the metastable liquid oxide phases. The state-of-art multicomponent solution thermodynamic models and databases are applied to describe the entropy changes and predict the wetting behaviors. Our results show that by chemically softening either the liquid or the solid phase, the wetting angle reduces. And an effective soften agent/additive (either in the form of chemical elements or molecules) will weaken the bonds within the liquid (or solid) phase and promote new bonds at the interfaces, thus increasing the interface entropy. Subsequently, as an example, Ti and Zr are proposed as effective softening elements to improve the wetting of aluminum liquid on B6Si(s). This approach provides a concept and tool to advance research in catalytic chemistry, nucleation (growth), elastowetting, and cell-substrate interactions.

Low-Temperature Molten Salt Electrolytes for Membrane-Free Sodium Metal Batteries

The liquid metal battery (LMB) is attractive due to its simple construction, its circumvention of solid-state failure mechanisms and resultantly long lifetimes, and its particularly low levelized cost of energy. Here, we provide a study of a unique binary electrolyte, NaOH-NaI, in order to pursue a low-cost and low-temperature sodium-based liquid metal battery (LMB) for grid-scale electricity storage. Thermodynamic studies have confirmed a low eutectic melting temperature (220°C) as well as provided data to complete the phase diagram of this system. X-ray diffraction has further supported the existence of a recently discovered compound, Na7(OH)5I2, as well as offered initial evidence toward a NaI-rich compound displaying Pm-3m symmetry. These phase equilibrium data have then been used to optimize parameters from a two-sublattice thermodynamic solution model to provide a starting point for study of higher order systems. Further, a detailed electrochemical study has identified the voltage window and related oxidation/reduction reactions and found greatly improved stability of the pure sodium electrode against the electrolyte. Finally, an Na|NaOH-NaI|Pb-Bi proof-of-concept cell was assembled. This cell achieved over 100 cycles and displayed leakage currents below 0.40 mA/cm2. These results highlight an exciting class of low-melting molten salt electrolytes that may enable low cost grid-scale storage.

First principles modeling of the temperature dependent ternary phase diagram for the Cu–Pd–S system

As an aid to the development of hydrogen separation membranes, we predict the temperature dependent phase diagrams using first principles calculations combined with thermodynamic principles. Our method models the phase diagram without empirical fitting parameters. By applying thermodynamic principles and solid solution models, temperature-dependent features of the Cu–Pd–S system can be explained, specifically solubility ranges for substitutions in select crystalline phases. Electronic densities of states calculations explain the relative favorability of certain chemical substitutions. In addition, we calculate sulfidization thresholds for the Pd–S2 system and activities for the Cu–Pd binary in temperature regimes where the phase diagram contains multiple solid phases.