Thermodynamic Calculations Research Articles

Thermodynamic modeling of pressure-dependent phase diagram in alkali metals Li, Na and K

The high-pressure behavior of the alkali metals has attracted much attention in both experimental and theoretical aspects. This study is focused on the thermodynamic optimization of the temperature and pressure dependence of the molar volumes, the compressibility and phase diagrams of Li, Na and K according to the CALPHAD method. The pressure- temperature phase diagrams of lithium, sodium and potassium up to 50-100 GPa were calculated using the obtained thermodynamic parameters. The available experimental data, such as extremely low melting temperatures at high pressure, pressure-induced structural transitions between simple bcc and fcc crystals and the molar volume changes with the increasing pressure, were well reproduced in our calculations. The good agreements between our calculations and the experiments assessed in the literature indicated that our thermodynamic parameters are reasonable. Our thermodynamic calculations would assist to understand the phase transitions and structural properties of alkali metals at high pressure.

Synergistic effects of Monel 400 filler wire in gas metal arc welding of CoCrFeMnNi high entropy alloy

Weldability plays a crucial role in the journey of high entropy alloys towards their engineering applications. In this study, gas metal arc welding was performed to join an as-rolled CoCrFeMnNi high entropy alloy using Monel 400 as the filler wire. The present research findings demonstrate a favorable metallurgical chemical reaction between the Monel 400 filler and the CoCrFeMnNi high entropy alloy, resulting in compositional mixing within the fusion zone that promotes a solid-solution strengthening effect, counteracting the typical low hardness associated to the fusion zone of these alloys. The weld thermal cycle induced multiple microstructure changes across the joint, including variations in the grain size, existing phases and local texture. The grain size was seen to increase from the base material toward the fusion zone. An FCC matrix and finely sparse Cr-Mn-based oxides existed in both base material and heat affected zone, while in the fusion zone new FCC phases and carbides were formed upon the mixing of the Monel 400 filler. The role of the filler material on the fusion zone microstructure evolution was rationalized using thermodynamic calculations. Texture shifted from a γ-fiber (in the base material) to a strong cubic texture in the fusion zone. Digital image correlation during tensile testing to fracture coupled with microhardness mapping revealed that, stemming from the process-induced microstructure changes, the micro and macromechanical response differed significantly from the original base material. This study successfully established a correlation between the impact of the process on the developed microstructural features and the resultant mechanical behavior, effectively assessing the processing-microstructure-properties relationships towards an improved understanding of the physical metallurgy associated to these advanced engineering alloys. In conclusion, this work provides an important theoretical framework and practical guidance for optimizing the engineering applications of high entropy alloys.

Combined experimental and CALPHAD investigation of equimolar AlCoCrFeNiX (X=Mo,Ta,W) High-Entropy Alloys

Aiming to evaluate the effect of refractory metal additions to a quinary AlCoCrFeNi High-Entropy Alloy (HEA), three novel equimolar AlCoCrFeNi-X (X = Mo, Ta, W) HEAs were designed, arc-melted, annealed, and characterized by SEM-EDS, XRD and microhardness measurements. CALPHAD thermodynamic calculations were exploited to design compositions and thermal treatments of the selected HEAs as well as to predict constitution and interpret microstructure of the samples. On the other hand, the experimental results contributed to the validation of the in-house built GHEA thermodynamic database (including the Al, Co, Cr, Fe, Ni, Mo, Ta, W elements) used for the calculations. No TCP intermetallic was found to form in the quinary AlCoCrFeNi alloy. However, the formation of σ, Laves-C14 and μ phases was observed in the samples containing Mo, Ta, and W, respectively, in agreement with the most accepted VEC-based phases stabilization criteria. The addition of the refractory metals led to a microhardness increase for all the investigated alloys. Overall, good agreement was observed between experiments and calculations, especially for compositional trends and phase amounts, allowing the database validation and supporting its applicability to phase equilibria simulation in the six-component HEAs belonging to the Al–Co–Cr–Fe–Ni-X (X = Mo, Ta, W) systems.

Temperature dependence mechanism of high-temperature oxidation of transition metal silicide MoSi2

Transition metal silicides represented by MoSi2 have excellent oxidation resistance and are widely used as high-temperature anti-oxidation coatings in hot end components of power equipment. However, the mechanism of temperature-dependent growth of MoSi2 oxidation products has not been revealed. Therefore, this study investigated the formation characteristics of oxide film and silicide-poor compound on MoSi2 at temperatures of 1000 °C–1550 °C through high-temperature oxidation experiments, combined with microscopic Raman spectroscopy, scanning electron microscope, and x-ray diffraction (XRD) characterizations. The result showed that MoSi2 underwent high-temperature selective oxidation reactions at 1000 °C–1200 °C, forming MoO2 and SiO2 oxide film on the substrate. As the oxidation temperature increased to 1550 °C, after 100 h of oxidation, along with the disappearance of MoO2 and the phase transformation of SiO2, a continuous Mo5Si3 layer with a thickness of approximately 47 μm was formed at the SiO2–MoSi2 interface. Thermodynamics and kinetic calculations further revealed the mechanism of temperature-dependent growth of oxidation products (MoO2 and Mo5Si3) during high-temperature oxidation process of MoSi2. As the temperature increased, the diffusion flux ratio of O and Si decreased, leading to a decrease in oxygen concentration at the interface and promoting the growth of the Mo5Si3 layer. Its thickness is an important indicator for evaluating the oxidation resistance of MoSi2 coatings during service. This study provides experimental and mechanistic insights into the temperature-dependent growth behavior of Mo5Si3 during the high-temperature oxidation of MoSi2 coating, and provides guidance for predicting the service life and improving the oxidation resistance of silicide coatings.

Carbide Precipitation Behavior of High‐Alloy Steel During Solidification and Cooling Process

The precipitation, growth, and transformation of carbides rich in Cr and Mo during solidification and cooling process of high‐alloy steel for cold working dies are investigated. The Fe–C pseudobinary phase diagram of high‐alloy steel is calculated by Thermo‐Calc software to ascertain the critical phase transformation temperatures. The temperatures of phase transformation during the solidification process are determined by a differential scanning calorimeter. Then the microstructure of the samples at these characteristic temperatures is observed in situ by high‐temperature confocal microscope. The results show that the characteristic temperatures for phase transformation and carbide precipitation are 1380, 1315, 1140, and 980 °C, respectively. At 1315 °C, thick rod‐like or island‐like M7C3 carbides enriched in Cr and Fe are formed. At 1140 °C, secondary M7C3, adhering to the primary eutectic M7C3, grows rapidly in a rod‐like morphology and maintains a similar composition. The secondary M6C carbides of segregated Mo elements precipitate in fan‐shaped clusters near M7C3 through the dissolution of M7C3 and the conversion of M2C. Thermodynamic calculation further indicates that the eutectic Cr7C3 precipitates at 1213 °C, and secondary Cr7C3 remains under conditions favorable for precipitation below the solidus, preceding the precipitation of secondary carbides Cr23C6 and Mo2C.

Stabilization of Uranium in Acid Ore Wastewater through Hydrothermal Mineralization-Induced Crystallization.

Uranium [U(VI)] mining activity resulted in the discharge of uranium containing acid wastewater. It is necessary for immobilizing the uranium from wastewater to avoid its environmental pollution. In this work, a novel hydrothermal mineralization strategy is proposed for uranium stabilization. Three reaction systems such as Mg3(PO4)2 + UO22+, Mg2+ + PO43- + UO22+, and Mg2+ + PO43- + Mg3(PO4)2 + UO22+ were designed to investigate the uranium mineralization and stabilization performance. The consumed molar quantities of magnesium and phosphate were calculated to understand the mineralization mechanisms. The molar ratios of Mg/U and P/U in the experimental results were in agreement with those of thermodynamic calculation in the presence of dissolved Mg2+ and PO43- under the hydrothermal process. The calculated saturated index indicated the facile crystallization of uranium into the saleeite and chernikovite through hydrothermal mineralization at the pH value of 5 and 473 K. Crystallization into saleeite and chernikovite contributed to uranium stabilization, resulting in the negligible leaching rate of 5% due to the high crystallinity of 97.23%. Thus, hydrothermal mineralization of uranium crystallization into saleeite and chernikovite was promising for uranium stabilization with long-term stability.

Efficient separation in n‐butyl ether production process from computational thermodynamics to process intensification

Efficient separation in <i>n</i>‐butyl ether production process from computational thermodynamics to process intensification

Advanced design and optimization of tailored refining fluxes for the purification of Mg–Li alloys

This study systematically investigates the influence of integrating KCl into the refining flux on the purification efficiency of Mg–Li alloy. The findings reveal that an optimal purification effect is achieved with a 50 % addition of KCl to the refining flux, resulting in a remarkable 56 % reduction in volume fraction of inclusions to 0.17 % and an 80 % improvement in elongation to 29.1 %. The developed novel quaternary refining flux is composed of KCl + LiCl + LiF + CaF2 (3:3:1:2, wt.%). Based on thermodynamic calculation and analysis, the purification mechanism is elucidated, demonstrating that KCl enhances purification efficiency by reducing flux and melt viscosity, improving wettability, increasing contact area, and facilitating flux adsorption on inclusions. Excessive KCl addition hinders purification by decreasing flux density, slowing settling velocity, and affecting the purification process. The quaternary flux, applying to industrial Mg–Li alloy scrap, demonstrates outstanding purification performance with a 73 % reduction in inclusion volume fraction to 0.33 % and a remarkable 584 % increase in elongation to 17.1 %. The development and application of a novel Mg–Li alloy flux are of significant importance for promoting the industrial development of Mg–Li alloys.

Sulfide oxidation by members of the Sulfolobales

Abstract The oxidation of sulfur compounds drives the acidification of geothermal waters. At high temperatures (&amp;gt;80°C) and in acidic conditions (pH &amp;lt;6.0), oxidation of sulfide has historically been considered an abiotic process that generates elemental sulfur (S0) that, in turn, is oxidized by thermoacidophiles of the model archaeal order Sulfolobales to generate sulfuric acid (i.e., sulfate and protons). Here, we describe five new aerobic and autotrophic strains of Sulfolobales comprising two species that were isolated from acidic hot springs in Yellowstone National Park (YNP) and that can use sulfide as an electron donor. These strains significantly accelerated the rate and extent of sulfide oxidation to sulfate relative to abiotic controls, concomitant with production of cells. Yields of sulfide-grown cultures were ∼2-fold greater than those of S0-grown cultures, consistent with thermodynamic calculations indicating more available energy in the former condition than the latter. Homologs of sulfide:quinone oxidoreductase (Sqr) were identified in nearly all Sulfolobales genomes from YNP metagenomes as well as those from other reference Sulfolobales, suggesting a widespread ability to accelerate sulfide oxidation. These observations expand the role of Sulfolobales in the oxidative sulfur cycle, the geobiological feedbacks that drive the formation of acidic hot springs, and landscape evolution.

Thermodynamic descriptions of the CaO–Al2O3 and CaO–Al2O3–SiO2 systems over the whole composition and temperature ranges

AbstractThe CaO–Al2O3–SiO2 system is a fundamental system in aluminosilicate materials, and its thermodynamic description provides key information for ceramic design, cement production, slag tapping, and geological prediction. However, the existing thermodynamic calculations for the CaO–Al2O3 system show inaccurate heats of formation for the compounds and consequently a decomposition of the CA2 (CaO⋅2Al2O3) phase at a low temperature. Besides, the solid solutions in anorthite and cristobalite have never been considered in the previous thermodynamic assessments for the CaO–Al2O3–SiO2 system. Therefore, thermodynamic reassessments of the CaO–Al2O3 and CaO–Al2O3–SiO2 systems are carried out in the present work using the CALculation of PHAse Diagram method, considering the solid solution in anorthite and cristobalite for the first time. The anorthite and cristobalite phases are modeled based on the individual mechanism of solid solution, with the anorthite described by (Ca+2, Va)1(Al+3, Si+4)2(Si+4)2(O−2)8 and the cristobalite described by (Va, Ca+2)1(Si+4, Al+3)2(O−2)4. The present assessment solves the above issues and provides consistent thermodynamic descriptions for the liquid and solid phases. Based on the established thermodynamic database, a Scheil solidification simulation is carried out for a cement clinker and the variations of mass fractions of the phases as well as the composition of liquid during Scheil cooling are calculated. The present work guides the design of relevant materials and lays an essential foundation for the establishment of the thermodynamic database of multicomponent aluminosilicate materials.

Research on the interaction of burden gangue phases based on thermodynamic calculation

Research on the interaction of burden gangue phases based on thermodynamic calculation

Experimental investigation and thermodynamic analysis of TiC–Fe cermets with Mo additions

Abstract In this study, the effects of Mo additions on the microstructure, hardness and bending strength of TiC–Fe cermets manufactured by spark plasma sintering were investigated by scanning electron microscopy, X-ray diffraction and mechanical properties tests. Thermodynamic calculations were utilized to analyze the evolution of the microstructure. The results show that the conventional core/rim structure was not formed during the solid-phase sintering of TiC–Fe cermets. The heat-treatment process and reasonable Mo addition can effectively enhance the overall performance of the alloys. With the addition of minor Mo, the hardness of the sintered cermets improved significantly, which was attributed to the solid solution strengthening mechanism of Mo in Fe binder. However, excessive Mo exceeded the solubility range of Fe binder and precipitated in the form of M 6C and Mo2C phases, which damaged the bending strength of the heat-treated cermets.

Hydrogenation of Covalent Organic Framework Induces Conjugated π Bonds and Electronic Topological Transition to Enhance Hydrogen Evolution Catalysis.

Recently, many topological materials have been discovered as promising electrocatalysts in chemical conversion processes and energy storage. However, it remains unclear how the topological electronic states specifically modulate the catalytic reaction. Here, the two-dimensional metal phthalocyanine-based covalent organic framework (MPc-COF) is studied by ab initio thermodynamic calculations to clearly reveal the promotional effect on the electrochemical hydrogen evolution reaction (HER) induced by topological gapless bands (TGBs). We find that the prehydrogenated (and fluorinated) H4CdPc-COF(F) shows the best HER performance, with 0.016 V (near zero) overpotential. By tracking changes to the electronic structure and free energy as the prehydrogenation and HER processes occur, we are able to separately attribute the high HER efficiency in part due to the increase of the electron bath by donating electrons to the conjugated π bonds and also to the existence of TGBs. Specifically, the significant catalytic promotion by TGBs is proven to decrease the free energy by 0.218 eV to near zero. When the TGBs are destroyed, e.g., by replacing N with P and opening a band gap, the HER efficiency is reduced. This study opens avenues for deterministically harnessing topological band features to improve electrocatalysis.

When covalent organic frameworks meet zeolites: Enhancing rhodamine B removal through the synergy in the emerging organic–inorganic nanoadsorbents

The development of new porous materials has attracted intense attention as adsorbents for removing pollutants from wastewater. However, pure inorganic and organic porous materials confront various problems in purifying the wastewater. In this work, we integrated a covalent organic framework (TpPa-1) with an inorganic zeolite (TS-1) for the first time via a solvothermal method to fabricate new-type nanoadsorbents. The covalent organic framework/zeolite (TpPa-1/TS-1) nanoadsorbents combined the merits of the zeolite and COF components and possessed efficient adsorptive removal of organic contaminants from solution. Structural morphology and chemical composition characterization by powder X-ray diffraction, scanning electron microscopy, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy and thermogravimetric analysis demonstrated the successful preparation of TpPa-1/TS-1 composite nanoadsorbents. The resultant composite adsorbent TpPa-1/TS-1 removed rhodamine B at 1.7 and 2.6 times the efficiency of TpPa-1 and TS-1, respectively. Additional investigation revealed that the Freundlich adsorption isotherm and the pseudo-second-order kinetic model could be employed to represent the adsorption process more appropriately. Thermodynamic calculation analysis showed that the adsorption process proceeded spontaneously and exothermically. Besides, the effects of pH, absorbent mass and ionic strength on the adsorption performance were systematically investigated. The prepared composite adsorbent showed a slight decrease in removal efficiency after eight cycles of repeated use, and real water environment experiments also showed the high stability of the adsorbent. The enhanced performance can be attributed to electrostatic interaction, acid-base interaction, hydrogen bonding and π–π interactions.

Design of advanced steels by integrated computational materials engineering

AbstractThe integrated computational materials engineering (ICME) has achieved great success in accelerating the rational design and deployment of new materials. It is a new route of designing new materials and processes and highlighted by Materials Genome Initiative/Engineering that stresses the high‐throughput computation in addition to high‐throughput experimentation and materials informatics. This article presents a brief review on the basic theories and multi‐scale computational tools of ICME to design advanced steel grades, including the first‐principles calculations, the CALPHAD method (i.e., computational thermodynamics) fueled by dedicated databases, diffusion and phase‐field simulations, as well as finite analysis methods and machine learning. In the ICME scheme to deal with steels, the CALPHAD method is considered as the core to readily consider multi‐component systems and integrated to link the microscopic simulations (such as diffusion and phase field method to predict microstructure evolutions in response to external conditions) and macroscopic finite analysis method to deal with mechanical properties. Two applications are also presented to address the new routes to carry out materials design, especially for advanced steels.

Thermodynamic assessment of the Ce[sbnd]H and CeNi5[sbnd]H system

Interstitial metal hydrides (MHs) have attracted considerable attention in the field of hydrogen technology, particularly in the context of storage and compression applications. Because of their minor hysteresis effects, good cyclability, activation simplicity, and high volumetric storage density, LaNi5-based alloys are recognized as prominent candidates for hydrogen storage application. Additionally, the system’s thermodynamic and electrochemical properties can be modified to suit the requirements of a particular application by alloying specific substituents. To ascertain the thermodynamic effects of Ce addition within LaNi5, in this work the CeH and CeNi5H systems have been modeled with the CALPHAD method. For this reason, in this work, two different thermodynamic models have been developed and assessed using the same pressure-composition isotherms (PCIs) datasets obtained from literature and theoretical formation energies newly calculated employing periodic density functional theory (DFT). Direct comparison of the models against each other in terms of accuracy and physical plausibility revealed that extrapolation of thermodynamic properties to data-scarce regions is more reasonable with fewer model parameters and in agreement with other similar systems within the rare-earth (RE) metal-hydride class. In addition, the CeNi5H system was investigated by assessing the (Ce)(Ni)5(V a,H)7 phase model, which could accurately predict hydrogen storage properties while being compatible with previously developed LaNi5H models. Ultimately, the models developed in this study may be employed and extended to describe multi-component REH systems and allow for thermodynamic computations that are highly desirable for accurate predictions of hydrogen absorption/desorption properties and degradation characteristics within the (La,Ce)Ni5H metal hydride family.

Facile synthesis of anthranilic acid based dual functionalized novel hyper cross-linked polymer for promising CO2 capture and efficient Cr3+ adsorption

A novel hyper cross-linked polymer of 2-Aminobenzoic acid (HCP-AA) is synthesized for the adsorption of Cr3+ and CO2. The Brunauer–Emmett–Teller surface area of HCP-AA is 615 m2 g−1. HCP-AA of particle size 0.5 nm showed maximum adsorption of Cr3+ for lab prepared wastewater (93%) while it was 88% for real industrial wastewater. It is might be due to electrostatic interactions, cation-π interactions, lone pair interactions and cation exchange at pH 7; contact time of 8 min; adsorbent dose 0.8 g. The adsorption capacity was calculated 52.63 mg g−1 for chromium metal ions at optimum conditions. Freundlich isotherm studies R2 = 0.9273 value is the best fit and follows pseudo second order kinetic model (R2 = 0.979). The adsorption is found non-spontaneous and exothermic through thermodynamic calculations like Gibbs free energy (ΔG), enthalpy change (ΔH) and entropy change (ΔS) were 6.58 kJ mol−1, − 60.91 kJ mol−1 and − 45.79 kJ mol−1 K−1, respectively. The CO2 adsorption capacity of HCP-AA is 1.39 mmol/g with quantity of 31.1 cm3/g (6.1 wt%) at 273Kwhile at 298 K adsorption capacity is 1.12 mmol/g with quantity 25.2 cm3/g (5 wt%). Overall, study suggests that carboxyl (–COOH) and amino (–NH2) groups may be actively enhancing the adsorption capacity of HCP-AA for Cr3+ and CO2.

The Influence of Rare Earth Ce on the Microstructure and Properties of Cast Pure Copper.

The effects of rare earth Ce on the microstructure and properties of cast pure copper were investigated through thermodynamic calculations, XRD analysis, mechanical testing, metallographic microscopy, and scanning electron microscopy (SEM). The experimental results demonstrate that the reaction between rare earth Ce and oxygen as well as sulfur in copper exhibits a significantly negative Gibbs free energy value, indicating a strong thermodynamic driving force for deoxidation and desulfurization reactions. Ce is capable of removing trace amounts of O and S from copper. Moreover, the maximum solid solubility of Ce in Cu falls within the range of 0.009% to 0.01%. Furthermore, Ce can refine columnar grains while enlarging equiaxed grains in as-cast copper. Upon the addition of rare earth Ce, the tensile strength increased by 8.45%, elongation increased by 12.1%, and microhardness rose from 73.5 HV to 81.2 HV-an increase of 10.5%. Overall, rare earth Ce has been found to enhance both the microstructure and mechanical properties of cast pure copper.

Microstructural Characterization of AlCrCuFeMnNi Complex Concentrated Alloy Prepared by Pressureless Sintering.

A significant and increasing number of studies have been dedicated to complex concentrated alloys (CCAs) due to the improved properties that these metallic materials can exhibit. However, while most of these studies employ melting techniques, only a few explore powder metallurgy and pressureless sintering as production methods. In this work, a microstructural characterization of AlCrCuFeMnNi CCA samples obtained by powder metallurgy and pressureless sintering using mixtures of powders with different compositions was carried out. One batch of samples (B1) was prepared using commercial powders of Al, Cr, Cu, Fe, Mn, and Ni. Another batch (B2) used mixtures of CrFeMn, AlNi, and Cu powders. A third set of samples (B3) was obtained by adding 1% at. of Mg to the B2 powder. The samples were characterized by X-ray diffraction, scanning and transmission electron microscopy, energy dispersive spectroscopy, density measurements, and hardness tests. Thermodynamic calculations were also used to complement the microstructural characterization. All the obtained samples exhibited high relative density and hardness values. However, B3 samples showed a higher hardness, attributed to the finer distribution of oxide particles, which was promoted by the presence of Mg during sintering. These last samples presented a hardness/density ratio of 62 HV/(g cm-3), surpassing that of some martensitic stainless steels and nickel-titanium alloys.

Epoxidation of Camelina sativa oil methyl esters as a second-generation biofuel with thermodynamic calculations

The epoxidation of methyl esters found in Camelina sativa (CS) non-edible oil — largely containing unsaturated fatty acids — was performed. Epoxides are known to be used in biopolymer formation and CO2 capture. This study distinctively demonstrates epoxidation process through a combination of statistical methods and quantum chemical thermodynamic calculations. Esters produced along with glycerol during transesterification of vegetable oils can be used efficiently through epoxidation. Epoxidation products synthesized at various reaction conditions (including oil refinement) were analyzed through gas chromatography with mass spectrometry. According to the statistical analysis, the reaction time and temperature had the highest effect on the composition of products and oil refining is unnecessary. Moreover, iodine values (ester conversion) were determined without the use of chemicals through Raman spectroscopy. The study findings indicate CS epoxidation to be an environment-friendly process.