Thermodynamic Predictions Research Articles

Coordinated chemical and microstructural analyses of presolar silicate grains from AGB/RGB stars and supernovae in the CO3.0 chondrite Dominion Range 08006

AbstractWe report the structural and chemical analyses of six presolar silicate grains identified in situ in the CO3.0 carbonaceous chondrite Dominion Range (DOM) 08006. Two of the grains have O‐isotopic compositions consistent with origins in the circumstellar envelopes of low‐mass (<2M☉) asymptotic giant branch (AGB)/red giant branch (RGB) stars, although without Mg‐isotopic data, origins in supernovae (SNe) cannot be ruled out. The other four grains have O‐isotopic compositions consistent with origins in the ejecta of type‐II SNe. Transmission electron microscopy analyses reveal that all grains are crystalline (single crystal or polycrystalline) and have varied compositions. The analyzed AGB/RGB grains include an Fe‐rich crystalline olivine with an Fe‐sulfide inclusion and a chemically zoned olivine grain that also contains an Fe‐oxide rim. The grains derived from SNe include two polycrystalline assemblages with structures that overlap with both olivine and pyroxene, an assemblage composed of both a single crystal of forsterite and polycrystalline forsterite, and an orthopyroxene grain with an embedded Fe‐sulfide crystal. The thermodynamic origins of both AGB/RGB and SN grains are also diverse. The structure and compositions of two grains are consistent with equilibrium thermodynamic predictions of condensation, whereas four are not, suggesting formation through nonequilibrium or multistep processes. Our observations of presolar silicate grains suggest that the circumstellar envelopes of AGB/RGB stars and the ejecta of SNe can produce grains with comparable structures and compositions.

A functionally graded material design from stainless steel to Ni-based superalloy by laser metal deposition coupled with thermodynamic prediction

Extreme performance requirements are demanding materials with functional microstructure and properties. Additive manufacturing (AM) is an efficient method to fabricate functionally graded materials (FGMs) with gradually variable composition and structures as a function of position. In this work, a powder-based laser directed energy deposition (LDED) process was carried out to develop a series of compositionally graded joints from 316 stainless steel to Inconel 718 alloy. The microstructure, composition, precipitation transformation and mechanical properties were investigated as a function of position in FGMs via experimental characterization and computational analysis. The 75 wt% IN718 component with fine and equiaxial grains is directly obtained from the laser deposition. The diffusion and segregation of Ni, Nb and Ti elements underly the transformation mechanism between Laves, NbNi3/δ, γ'' and γ'' phases during aging, which has a high consistency with the computational prediction. The precipitation transformation has a close relationship with the final mechanical properties of the FGM. The computational-experimental approach is a promising method to tune the microstructure-property relationship of dissimilar metal joints. The gradient precipitation that can be flexibly tuned by LDED process provides a high throughput design to develop new functional materials with local tailoring of properties.

Preparation of vanadium by the magnesiothermic self-propagating reduction and process control

Abstract A new process for preparing vanadium by direct reduction of V2O5 from the Mg–V2O5 self-propagating system is proposed in this article. The reaction behavior and path of V2O5 in the magnesiothermic reduction process were investigated using the XRD, SEM-EDS, laser particle size analyzer, and specific surface area analyzer. The experimental results show that the reaction of the V2O5–Mg system is a solid-solid reaction, and the initial reaction temperature is 570°C. Although the formation of MgV2O4 spinel cannot be predicted via the calculation of thermodynamics, the presence of MgV2O4 spinel is of great significance to the V2O5 reduction process. Taking into account the characteristics of the gradual reduction of V2O5 by Mg and the appearance of the MgV2O4 spinel phase, the limiting link of the reaction may be the transition from MgV2O4 to V. A reduction path of V2O5 beyond the thermodynamic prediction is proposed: V2O5 → V3O5 → MgV2O4 → V. The reaction temperature and the phase transformation process can be effectively controlled by adjusting the ratio of reactants and additives, and element V can be obtained by a one-step rapid self-propagating reaction and breaking through the reaction restriction link. In this experiment, the vanadium powder with a porous structure, a specific surface area of 3.44 m2 g−1, and the oxygen content of 4.86 wt% were obtained.

Unveiling the role of filler surface energy in enhancing thermal conductivity and mechanical properties of thermal interface materials

With heat-flux density of electronics drastically increase polymer-based thermal interface materials play a critical role in the performance of electronics. Although surface energy of fillers has been recognized as a crucial parameter, the exploitation of the filler surface energy-dependent properties is still unclear. Herein, we report on unveiling the effect of the surface energy of aluminum on thermal and mechanical properties in thermal interface materials consisted of polydimethylsiloxane and modified aluminum with silane-coupling agents containing varied chain lengths. The results show that reducing the surface energy of aluminum is beneficial to improve the aluminum fillers dispersibility in polydimethylsiloxane, leading to improved macroscopic properties, including rheology, mechanical properties, and thermal properties. Furthermore, based on the thermodynamic prediction, a winding hypothesis was proposed to explain the interaction between the modified aluminum and polydimethylsiloxane. This work provides valuable guidance for rationally designing the surface energy of fillers in thermal interface materials.

Alum and Gypsum Amendments Decrease Phosphorus Losses from Soil Monoliths to Overlying Floodwater under Simulated Snowmelt Flooding

Phosphorus (P) loss from soils poses a threat of eutrophication to downstream waterbodies. Alum (Al2(SO4)3·18H2O) and gypsum (CaSO4·2H2O) are effective in reducing P loss from soils; however, knowledge on their effectiveness under cold temperatures is limited. This study examined the reduction of P loss from soils with alum and gypsum amendment under simulated snowmelt flooding. Intact soil monoliths (15 cm depth) collected from eight agricultural fields in flood-prone areas of Manitoba, Canada, were surface amended with alum or gypsum, pre-incubated for 2 weeks, then flooded and incubated at 4 °C for 8 weeks. Porewater and floodwater samples collected weekly were analyzed for dissolved reactive P (DRP), dominant cations and anions. An enhanced P release with flooding time was observed in all soils whether amended or unamended; however, alum/gypsum amendment reduced DRP concentrations in porewater and floodwater in general, with alum showing a more consistent effect across soils. The reduction in floodwater DRP concentrations (maximum DRP concentration during flooding) with alum and gypsum ranged from 34–90% and 1–66%, respectively. Based on Visual MINTEQ thermodynamic model predictions, precipitation of P and formation of P-sorbing mineral species with alum and gypsum amendment reduced DRP concentrations at latter stages of flooding.

Review of computational approaches to predict the thermodynamic stability of inorganic solids

Improvements in the efficiency and availability of quantum chemistry codes, supercomputing centers, and open materials databases have transformed the accessibility of computational materials design approaches. Thermodynamic stability predictions play a central role in the efficacy of these approaches and should be considered carefully. This review covers the fundamentals of calculating thermodynamic stability using first-principles methods. Stability is delineated into two main topics—stability with respect to decomposition into competing phases and stability with respect to phase transition into alternative structures at fixed composition. For each topic, a summary of the state-of-the-art is provided along with a tutorial overview of practical considerations. The application of machine learning to both kinds of stability predictions is also covered. Finally, the limitations of thermodynamic stability predictions are discussed within the context of predicting the synthesizability of materials.

Theoretical predictions of stability, electronic properties, elastic anisotropy, thermodynamics, and optical properties of MB2 (M = V, Nb, Zr)

Theoretical predictions of stability, electronic properties, elastic anisotropy, thermodynamics, and optical properties of MB2 (M = V, Nb, Zr)

Study of CMAS infiltration and evaporation behaviour under water vapour/sulphur oxide conditions in EB-PVD 7YSZ

The infiltration behaviour of CaO-MgO-Al2O3-SiO2 (CMAS) in Electron Beam Physical Vapour Deposited (EB-PVD) 7 wt% yttria stabilised zirconia (7YSZ) under controlled atmospheres (dry, wet and sulphurizing) was studied in detail. The microstructure of the CMAS-infiltrated 7YSZ and the CMAS residue on top were analysed to interpret the corrosion mechanisms. One of the major goals was to investigate the stability and the infiltration of CaSO4 into the 7YSZ columns. At the testing temperature of 1250 °C, CaSO4 was stabilised only under the SO2 atmosphere within the TBC coating and only in CaSO4-containing CMAS. Hydroxylation of CMAS elements was found under wet conditions, which changed the local CMAS composition and infiltration behaviour. These chemistry changes have provoked acidity changes in the CMAS which directly affected their aggressivity and viscosity. Thermodynamic equilibrium predictions on the volatility of CMAS components and the anhydrite stability under various atmospheres were used to understand the experimental findings and the underlying mechanisms.

Bridge functions of classical one-component plasmas.

In a recent paper, Lucco Castello etal. [arXiv:2107.03537] performed systematic extractions of classical one-component plasma bridge functions from molecular dynamics simulations and provided an accurate parametrization that was incorporated in their isomorph-based empirically modified hypernetted chain approach for Yukawa one-component plasmas. Here the extraction technique and parametrization strategy are described in detail, while the deficiencies of earlier efforts are discussed. The structural and thermodynamic predictions of the updated version of the integral equationtheory approach are compared with extensive available simulation results revealing a truly unprecedented level of accuracy in the entire dense liquid region of the Yukawa phase diagram.

Thermodynamic modeling of the sodium alanates and the Na–Al–H system

Abstract The thermodynamic properties of the Al –Na and Na–Al – H systems have been assessed by combining the “calculation of phase diagram” approach with first-principles predictions. The Gibbs energies of the individual phases were thermodynamically modeled, where the model parameters were obtained from best fit optimizations to combined experimental and first-principles predicted finite temperature data. The first-principles thermodynamic predictions were based upon density functional theory ground state minimizations and direct method lattice dynamics. The predictions proved to be important adjuncts to the assessments whenever experimental measurements were lacking or not feasible. It was shown that the phase stability conditions of sodium alanates, NaAlH4 and Na3AlH6, were well described with the present models.

Optimising the Al and Ti compositional window for the design of γ’ (L12)-strengthened Al–Co–Cr–Fe–Ni–Ti high entropy alloys

The effect of the relative contents of Al and Ti on the equilibrium phase formation in a novel Ni51Co18Fe5Cr10Al16-XTiX high entropy superalloy (HESA) system was analysed using Thermo-Calc software (TCHEA-3 database). The proposed HESAs showed a broad γ+γ′ equilibrium phase field over an extended temperature range (from 660 °C to a γ′-dissolution temperature >1184 °C) without the presence of brittle intermetallic phases. The effect of Al/Ti ratio on the microstructure, mechanical properties and precipitation strengthening of the HESAs was determined. The proposed alloys showed a high volume fraction (∼60%) of a (Ni, Co)3(Al, Ti)-type ordered (γ′) phase in a disordered face-centered cubic matrix phase (γ). The microstructure and the thermal properties of the HESAs showed excellent correlation to the theoretical thermodynamic predictions. A lower Al/Ti ratio improved the mechanical properties of the HESA system due to the high lattice misfit between the γ and γ′ phases. The homogenised and aged Ni51Co18Fe5Cr10Al8Ti8 HESA exhibited a γ′-volume fraction of 63%, γ′-dissolution temperature of 1200 °C and yield strengths of 1056 MPa and 852 MPa at room-temperature and 800 °C, respectively. The present work shows the potential to design Al–Co–Cr–Fe–Ni–Ti HESAs with a high volume fraction of γ′-phase and excellent mechanical properties.

Simultaneous extraction of lithium, rubidium, cesium and potassium from lepidolite via roasting with iron(II) sulfate followed by water leaching

Lepidolite is an important mineral resource containing lithium, rubidium, cesium and potassium. Most researches focused on the extraction of lithium from lepidolite, while the co-extraction of rubidium, cesium and potassium was ignored. In this study, the extraction of lepidolite at lower temperature was investigated by using iron(II) sulfates feedstock, aiming at enhancing the extraction of lepidolite, especially for rubidium and cesium. Thermodynamic predictions indicated that the co-extraction of lithium, rubidium, cesium and potassium from lepidolite by roasting with iron(II) sulfate was feasible, but high temperature worked against the extraction. The effects of process parameters on the extraction were investigated systematically. It was found that the optimal roasting conditions were as follows: 50% lepidolite particles <74 μm, temperature of 675 °C, iron(II) sulfate to lepidolite mass ratio of 2:1, and holding time of 90 min. The extraction efficiencies of Li, Rb, Cs and K were 92.7%, 87.1%, 82.6% and 86.2%, respectively. The reaction between lepidolite concentrate and iron(II) sulfate followed two pathways, i.e. gas-solid and liquid-solid reaction. The formation of pyrosulfates with low smelting point promoted the reaction by reacting with lepidolite through a circular transformation between sulfates and pyrosulfates. Compared with the conventional extraction of lepidolite, the proposed process operates at a lower temperature and co-extracts various metals, exhibiting great potential in industrial application.

Conversion of a CO–CO2 co‐feed with a porous tubular copper catalyst at low potential

AbstractIn the electrochemical reduction of CO2, copper electrodes are well known to be active and selective for a variety of products, depending on process conditions. However, the effect of feed composition on performance has not been extensively investigated, especially with respect to the conversion of CO2 to CO. We now show for copper electrodes in a porous tubular configuration (Hollow Fibre Electrodes, HFEs) at a relatively low working potential (−1.1 V vs Ag/AgCl), that an increasing concentration of CO in the feed results in a decreasing CO2 conversion rate to CO. Contrary, it is observed that the concomitant hydrogen production rate does not depend on the concentration of CO in the feed. These observations are in good agreement with thermodynamic predictions applying the equation for the Gibbs energy of reaction. On the basis of this conclusion, we anticipate that mass transfer limitations are minimized by the tubular morphology and flow‐through mode of operation. Most importantly, this study shows the necessity of a low CO concentration in the feed, to obtain a high CO2 conversion rate.

The Na–H system: from first-principles calculations to thermodynamic modeling

Abstract The Na–H system thermodynamic properties were assessed using Gibbs free energy model parameters obtained from best fit optimizations to combined experimental and first-principles predicted data. The first-principles finite temperature thermodynamic property predictions, based upon density functional theory ground state minimizations and direct method lattice dynamics, were used to supplement the Na–H dataset wherever experimental information was unavailable or unattainable. The predictions proved to be important for extending the evaluation of the heat capacity of the stable NaH phase to cover the complete 0 – 2000 K temperature range. The predicted thermodynamic properties of the hypothetical NaH3 end-member representing complete interstitial H substitution in solid body-centered cubic Na, provided a physical basis for modeling H dissolution in the Na lattice. The modeling also showed satisfactory agreement with experimental measurements of NaH enthalpies of formation, NaH decomposition pressures, and H solubility in liquid Na.

The microstructure of high manganese TWIP steels produced via simulated direct strip casting

Three TWIP steels based on the composition Fe-23Mn-3Si-3.3Al with different carbon concentrations were examined. The alloys were produced by rapid solidification in an experimental apparatus designed to simulate direct strip casting conditions. Examination of the driving force for solidification for this alloy showed the preference for BCC and FCC solidification were very close for this composition, within 10% of one another. This factor combined with the high undercooling resulted in the change in the primary solidified phase. Chemical analysis of the as-cast strip showed inter-dendritic segregation of Si and Al, but negligible segregation of Mn. A simple heat treatment was sufficient to chemically homogenise all alloys and produce microstructures comprising a fully austenitic structure, consistent with thermodynamic predictions.

A Functionally Graded Material Design from Stainless Steel to Ni-Based Superalloy by Laser Metal Deposition Coupled with Thermodynamic Prediction

A Functionally Graded Material Design from Stainless Steel to Ni-Based Superalloy by Laser Metal Deposition Coupled with Thermodynamic Prediction

Precipitation of aqueous transition metals in particulate matter during the dithiothreitol (DTT) oxidative potential assay.

Transition metals in particulate matter (PM) are hypothesized to have enhanced toxicity based on their oxidative potential (OP). The acellular dithiothreitol (DTT) assay is widely used to measure the OP of PM and its chemical components. In our prior study, we showed that the DTT assay (pH 7.4, 0.1 M phosphate buffer, 37 °C) provides favorable thermodynamic conditions for precipitation of multiple metals present in PM. This study utilizes multiple techniques to characterize the precipitation of aqueous metals present at low concentrations in the DTT assay. Metal precipitation was identified using laser particle light scattering analysis, direct chemical measurement of aqueous metal removal, and microscopic imaging. Experiments were run with aqueous metals from individual metal salts and a well-characterized urban PM standard (NIST SRM-1648a, Urban Particulate Matter). Our results demonstrated rapid precipitation of metals in the DTT assay. Metal precipitation was independent of DTT but dependent on metal concentration. Metal removal in the chemically complex urban PM samples exceeded the thermodynamic predictions and removal seen in single metal salt experiments, suggesting co-precipitation and/or adsorption may have occurred. These results have broad implications for other acellular assays that study PM metals using phosphate buffer, and subsequently, the PM toxicity inferred from these assays.

On the transferability of classical pairwise additive atomistic force field to the description of unary and multi-component systems: applications to the solidification of Al-based alloys.

Multi-component and multiphasic materials are continually being developed for electronics, aircraft, automotive, and general applications. Integrated Computational Materials Engineering (ICME) is a multiple-length scale approach that greatly benefits from atomistic scale simulations to explore new alloys. Molecular Dynamics (MD) allows to perform large-scale simulations by using classical interatomic potentials. The main challenge of using such a classical approach is the transferability of the interatomic potentials from one structure to another when one aims to study multi-component systems. In this work, the reliability of Zr, Al-Cu, Al-Cr and Al-Zr-Ti force field potentials is examined. It has been found that current interatomic potentials are not completely transferable due to the structure dependence from their parameterization. Besides that, they provide an appropriate description of unary and binary systems, notably for liquids, isotropic solids, and partially isotropic compounds. For solidification purposes, it has been found that coherent primary solidification of the FCC-phase in pure Al is highly dependent on the formalism to tune interatomic interactions. For Al-Cr alloys, the icosahedral short-range ordering (ISRO) increased by adding Cr to the melts. The different steps of solidification (formation of nuclei, effective germination of the α-Al phase and end of solidification) have been related to the evolution of the ISRO. The addition of Cr in melts prevented undercooling via icosahedral-enhanced nucleation of the α-Al phase. Precipitation of primary intermetallics in hyper-peritectic Al-Cr alloys was also tested. Contrary to classical thermodynamics predictions, α-Al phase was the primary precipitate for these alloys. This implies that Cr supersaturated the α-Al phase rather than forming intermetallic phases due to the high cooling rates.

Temperature in magnetic systems: Evolution towards thermal equilibrium by spin dynamics simulation

The concept of temperature in magnetic systems is examined by studying how two spin systems in thermal contact reach equilibrium. Using the spin dynamics simulation method, we consider two planar arrays of classical spins governed by the Heisenberg Hamiltonian, interacting with each other through an edge. According to an expression for the temperature of the system based solely on spin configurational degrees of freedom, we are able to obtain the temperature evolution with respect to time. The spin temperature follows an exponential behavior, and can be modeled by the Newton cooling law, reaching a common final temperature which is in complete agreement with the theoretical thermodynamic prediction. The simulation results give new insight on the meaning of temperature for magnetic systems and provide an operational method to calculate it in computer simulation.

Structure and Magnetic Properties of Thermodynamically Predicted Rapidly Quenched Fe85-xCuxB15 Alloys.

In this work, based on the thermodynamic prediction, the comprehensive studies of the influence of Cu for Fe substitution on the crystal structure and magnetic properties of the rapidly quenched Fe85B15 alloy in the ribbon form are performed. Using thermodynamic calculations, the parabolic shape dependence of the ΔGamoprh with a minimum value at 0.6% of Cu was predicted. The ΔGamoprh from the Cu content dependence shape is also asymmetric, and, for Cu = 0% and Cu = 1.5%, the same ΔGamoprh value is observed. The heat treatment optimization process of all alloys showed that the least lossy (with a minimum value of core power losses) is the nanocomposite state of nanocrystals immersed in an amorphous matrix obtained by annealing in the temperature range of 300–330 °C for 20 min. The minimum value of core power losses P10/50 (core power losses at 1T@50Hz) of optimally annealed Fe85-xCuxB15 x = 0,0.6,1.2% alloys come from completely different crystallization states of nanocomposite materials, but it strongly correlates with Cu content and, thus, a number of nucleation sites. The TEM observations showed that, for the Cu-free alloy, the least lossy crystal structure is related to 2–3 nm short-ordered clusters; for the Cu = 0.6% alloy, only the limited value of several α-Fe nanograins are found, while for the Cu-rich alloy with Cu = 1.2%, the average diameter of nanograins is about 26 nm, and they are randomly distributed in the amorphous matrix. The only high number of nucleation sites in the Cu = 1.2% alloy allows for a sufficient level of grains’ coarsening of the α-Fe phase that strongly enhances the ferromagnetic exchange between the α-Fe nanocrystals, which is clearly seen with the increasing value of saturation induction up to 1.7T. The air-annealing process tested on studied alloys for optimal annealing conditions proves the possibility of its use for this type of material.