Phase Thermodynamic Properties Research Articles

The elastic anisotropy, electronic and thermodynamic properties of TM5Si4 (TM= Sc, Y, Ti, Zr and Hf) silicides from first-principles calculations

In recent years, transition-metal silicon-based high temperature materials have attracted more and more attention due to their excellent physical and chemical properties. In this paper, we explored the phase stability, mechanical, anisotropy and thermodynamic properties of TM5Si4 (TM = Sc, Y, Ti, Zr and Hf) compounds by first-principles calculations. The results indicate that TM5Si4 compounds exhibit the thermodynamical and dynamical stability. And Hf5Si4 exhibits the best phase stability among five compounds. The orthorhombic Sc5Si4 and Y5Si4 are ductile, but the tetragonal Ti5Si4, Zr5Si4 and Hf5Si4 are brittle. The elastic anisotropies of TM5Si4 were demonstrated by the 3D contours and 2D projections of elastic modulus. The results confirm that the order of anisotropy is as follows: Zr5Si4 < Hf5Si4 < Ti5Si4 < Sc5Si4 < Y5Si4. TM-Si bonds can be formed in TM5Si4 silicides for the strong localized hybridization between TM-d and Si-3p states. Moreover, the thermal parameters confirm that five TM5Si4 silicides display the better thermal stability at elevated temperature.

Solid-liquid phase equilibrium and thermodynamic properties analysis of 2,4,5-trimethoxybenzaldehyde in mono-solvents

Solid-liquid equilibrium solubility of 2,4,5-trimethoxybenzaldehyde (ANH) in nineteen kinds of mono-solvents (i.e., methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol, s-butanol, n-pentanol, i-pentanol, acetone, 2-butanone, cyclohexanone, acetonitrile, N, N-dimethylformamide, tetrahydrofuran, ethyl formate, methyl acetate, ethyl acetate, and toluene) was determined by a gravimetric method over a temperature ranging from 278.15 K to 323.15 K under approximately 0.1 MPa. The solubility was positively correlated with temperature in all the selected solvents. The maximum solubility value occurred in DMF (x1 = 0.1923 mol·mol−1, T = 323.15 K) and the minimum solubility value occurred in i-propanol (x1 = 0.001971 mol·mol−1, T = 278.15 K). The modified Apelblat model, Yaws model, NRTL model and Wilson model were used to correlate the experimental data. The NRTL model fits best among all the models with RAD no larger than 0.0047 (ethanol) and a RMSD value less than 0.000236 (DMF). Dissolution properties of ANH, including dissolution enthalpy ΔdisH, dissolution entropy ΔdisS and dissolution Gibbs energy ΔdisG, were calculated according to the Wilson model. The dissolution process of ANH is demonstrated to be endothermic, spontaneous, and entropy-driven in the chosen mono-solvents. The solubility data, thermodynamic parameters and dissolution properties are of guiding significance to the further investigation of ANH.

Thermodynamic properties of the Yb-Sb system predicted from first-principles calculations

In the present work, thermodynamic properties of the Yb-Sb system have been studied by first-principles based quasiharmonic phonon approach, reporting the temperature-dependent isobaric heat capacity, entropy, formation enthalpy, isothermal bulk modulus, and thermal expansion. The effects by using different exchange-correlation functionals and the pseudopotentials on thermodynamic properties are examined. The results reveal that the combined Perdew-Burker-Ernzerhof functional revised for solids (PBEsol) together with the pseudopotential with all f-electrons frozen in the core is the best choice. This combination leads to an overall good description of the relative phase stabilities and thermodynamic properties, except for the rocksalt YbSb compound which is calculated to have an energy of ~25 kJ/mol-atom above the convex hull. The discrepancy is due probably to the change of the Yb valence states between the rocksalt YbSb structure and the other Yb-Sb compounds. Furthermore, the present calculations show that the Yb16Sb11 compound is stable. The analysis of stretching force constants demonstrates that the extremely strong Yb-Sb bonding is responsible for the stabilities of Yb11Sb10, Yb16Sb11, h-Yb5Sb3, and Yb4Sb3 at high temperatures.

Experimental study of the phase relations and thermodynamic properties of Bi-Se system

Experimental study of the phase relations and thermodynamic properties of Bi-Se system

Ising model on a body-centered cubic lattice with competing exchange interactions in strong magnetic fields

The effect of an external magnetic field on phase transitions, magnetic and thermodynamic properties of the antiferromagnetic Ising model on a body-centered cubic lattice with competing exchange interactions was studied using the replica algorithm of the Monte Carlo method. It is shown that a second-order phase transition is observed in the range of magnetic field values 7.0 ≤ H ≤ 10.0, and a first-order phase transition is observed in the range 11.0 ≤ H ≤ 13.0. A further increase in the magnetic field strength leads to the suppression of the phase transition.

Metastable and stable phase diagrams and thermodynamic properties of the cetyltrimethylammonium bromide (CTAB)/water binary system

The thermodynamic properties of the cationic surfactant cetyltrimethylammonium bromide (CTAB)/water system were investigated using differential scanning calorimetry (235–395 K) and adiabatic calorimetry (78–320 K), and the stable phase diagram was established, in which the locations of phase boundaries were precisely determined. The micellar phase and the lyotropic liquid crystalline (LC) phases were found to transform into a metastable gel phase via rapid cooling, and a metastable phase diagram was also constructed. The hexagonal LC phase was found to consist of two types of phases with different thermodynamic characteristics. The transitions from the separated two-phase “CTAB crystal + solution” to the micellar and LC phases were also investigated, and it was found that the transition occurs in a two-step manner, wherein the transitions at lower temperatures depended on the thermal history. The enthalpy of fusion of the ice that coexisted with the CTAB crystal did not provide any evidence for the CTAB crystal being hydrated by non-freezing water.

Mechanical alloying of the immiscible Cu-60wt%Cr alloy: Phase transitions, microstructure, and thermodynamic characteristics

Solid state alloying of immiscible alloy systems such as Cu-Cr is an important field of physical metallurgy. Currently, non-equilibrium techniques are successfully applied in the synthesis of Cu-Cr alloys; however, the mechanism of formation of these alloys remains unclear due to the unavailability of data regarding their microstructure evolution and thermodynamic characteristics. In this work, a mechanical alloying (MA) Cu-60wt%Cr alloy is prepared by high-energy milling. The phase transitions, thermodynamic properties, and microstructure of this alloy are analyzed using X-ray diffraction, differential scanning calorimetry, and transmission electron microscope techniques. The obtained results demonstrate that the supersaturated Cr(Cu) solid solution alloy has a supra-nanometer-sized microstructure and is composed of crystalline and amorphous phases. To form the alloy, the localized Cu is first transformed into an amorphous state, then the disordered Cu atoms diffuse into the Cr matrix during the MA process. The diffusivity of Cr atoms in the Cu lattice is significantly hindered, even when the lattice is heavily defected.

Solid-Phase Equilibria and Thermodynamic Properties of Phases in the Tm–Te System

Solid-Phase Equilibria and Thermodynamic Properties of Phases in the Tm–Te System

Charge-Order on the Triangular Lattice: A Mean-Field Study for the Lattice S = 1/2 Fermionic Gas.

The adsorbed atoms exhibit tendency to occupy a triangular lattice formed by periodic potential of the underlying crystal surface. Such a lattice is formed by, e.g., a single layer of graphane or the graphite surfaces as well as (111) surface of face-cubic center crystals. In the present work, an extension of the lattice gas model to fermionic particles on the two-dimensional triangular (hexagonal) lattice is analyzed. In such a model, each lattice site can be occupied not by only one particle, but by two particles, which interact with each other by onsite U and intersite and (nearest and next-nearest-neighbor, respectively) density-density interaction. The investigated hamiltonian has a form of the extended Hubbard model in the atomic limit (i.e., the zero-bandwidth limit). In the analysis of the phase diagrams and thermodynamic properties of this model with repulsive , the variational approach is used, which treats the onsite interaction term exactly and the intersite interactions within the mean-field approximation. The ground state () diagram for as well as finite temperature () phase diagrams for are presented. Two different types of charge order within unit cell can occur. At , for phase separated states are degenerated with homogeneous phases (but removes this degeneration), whereas attractive stabilizes phase separation at incommensurate fillings. For and only the phase with two different concentrations occurs (together with two different phase separated states occurring), whereas for small repulsive the other ordered phase also appears (with tree different concentrations in sublattices). The qualitative differences with the model considered on hypercubic lattices are also discussed.

Preparation and thermoelectric performance of tetrahedrite-like cubic Cu3SbS3 compound

Thermoelectric (TE) Cu3SbS3, as one of the Cu–Sb–S families, has the characteristic of strong anharmonicity of lattice vibrations. It may be a potential replacement for the unstable pristine tetrahedrite, provided that its cubic structure can be stabilised. In this study, pristine (near)-phase-pure cubic Cu3SbS3 and Fe-doped samples were successfully prepared by sequential use of equilibrium and non-equilibrium synthesis techniques. TE properties of both pristine and doped samples were optimised by tuning the sintering parameters. A maximum zT of 0.57 was achieved at 350 °C in pristine (near)-phase-pure cubic Cu3SbS3 sample hot pressed at 575 °C for 30 min, which is about 2.7 times higher than that of the spark plasma sintered one. The Fe-doped sample sintered at 575 °C for 45 min displays a higher zT in the whole testing temperature range and a maximum of 0.62 was reached at 350 °C. The influences of hot pressing and spark plasma sintering on the phase structure, microstructure, thermodynamic and TE properties were studied and correlated. The results demonstrated the potential of cubic Cu3SbS3 as a high-performance material.

Impact of salts on the phase separation and thermodynamic properties of mixed nonionic surfactants in absence/attendance of polyvinyl alcohol

Abstract Mixed surfactant systems are used in different applied fields like pharmaceutical formulation rather than single surfactant. Therefore, the determination of the clouding nature of the triton X-100 (TX-100) + Tween 80 (TW-80) mixture was carried out in H2O and polyvinyl alcohol (PVA). In the occurrence of PVA, the cloud point (CP) values of TX-100 initially enhance with enhancing the concentration of PVA and tend to decrease after a certain concentration. For different ratios of TX-100 and TW-80 mixture having the same concentration of both solutions, CP values increase through the decreasing ratios of TX-100 with/without PVA. In the presence of polymer, at higher ratios of TX-100 than TW-80, the CP values are higher in magnitudes in comparison to the aqueous medium but at lower ratios of TX-100, the value of CP are lower in magnitudes in comparison to the aqueous system. The CP values of the TX-100 + TW-80 mixture in the salt system are lower in magnitudes than the aqueous medium in both the absence/presence of PVA. However, a reduction of CP values was obtained to a large extent for Na2SO4 over NaCl in the case of lower volume ratios of TX-100. Various thermodynamic variables (standard free energy ( Δ G c o ${\Delta}{G}_{c}^{o}$ ), standard enthalpy ( Δ H c o ${\Delta}{H}_{c}^{o}$ ), standard entropy ( Δ S c o ${\Delta}{S}_{c}^{o}$ ) change, thermodynamic parameters of transfer (free energy of transfer ( Δ G c , t o ${\Delta}{G}_{c,t}^{o}$ ), and transfer of enthalpies ( Δ H c , t o ${\Delta}{H}_{c,t}^{o}$ )) of phase transition) were also determined.

Phase behavior, thermodynamic and rheological properties of ovalbumin/dextran sulfate: Effect of biopolymer ratio and salt concentration

The complexation between ovalbumin (OVA) and highly charged dextran sulfate (DS) was investigated employing phase behavior, zeta potential, confocal laser scanning microscope (CLSM), isothermal titration calorimetry (ITC) measurement, and dynamic rheometer analysis. The critical boundary pH values (pHc, pHϕ1, pHmax) were strongly dependent on the biopolymer ratio and salt concentration. Results of the phase diagram and zeta potential showed that the formation of complexes was mainly driven by strong electrostatic interactions. As the increase of the OVA/DS ratio, the critical pH values shifted to higher values. However, the addition of NaCl has a diverse effect, lower salt concentration (CNaCl <100 mM) promoted the formation of OVA/DS coacervates, while higher salt concentration (CNaCl≥ 100 mM) suppress the formation of coacervates due to the shielding effect. The ITC results revealed that DS does bind to native form of OVA at pH 7.0 through the electrostatic forces and it was a spontaneous exothermic process (△G < 0, △H < 0). Additionally, much higher viscoelasticity (G'&G″) for all OVA/DS coacervates indicates that the formation of a highly interconnected gel-like structure. The maximum viscoelasticity was shown at an OVA/DS ratio of 10:1 with 50 mM NaCl. On the other hand, the addition of salt decreased the gel transition temperature of OVA thus promote its aggregation in the mixing system. Our work provides important insight for understanding the interaction between sulfated polysaccharide with egg white protein.

Ab initio anharmonic thermodynamic properties of cubic CaSiO3 perovskite

We present an $\textit{ab initio}$ study of the thermodynamic properties of cubic CaSiO$_3$ perovskite (CaPv) over the pressure and temperature range of the Earth's lower mantle. We compute the anharmonic phonon dispersions throughout the Brillouin zone by utilizing the phonon quasiparticle approach, which characterizes the intrinsic temperature dependence of phonon frequencies and, in principle, captures full anharmonicity. Such temperature-dependent phonon dispersions are used to calculate $\textit{ab initio}$ free energy in the thermodynamic limit ($N \rightarrow \infty$) within the framework of the phonon gas model. Accurate free energy calculations enable us to investigate cubic CaPv's thermodynamic properties and thermal equation of state, where anharmonic effects are demonstrated. The present methodology provides an important theoretical approach for exploring phase boundaries, thermodynamic, and thermoelastic properties of strongly anharmonic materials at high pressures and temperatures.

Vapour-liquid phase equilibria and thermodynamic properties of solutions of the ethylbenzene and n-alkylbenzenes binary systems

The methods of theoretical description of the patterns of changes in thermodynamic properties depending on the composition and structure of solution components are a priority direction in the development of the theory of solutions. This article is devoted to the establishment of relationships between the thermodynamic properties, composition of solutions, and the structure of their components. The study of the thermodynamic properties of binary solutions formed by a common solvent (ethylbenzene) and substances of the homologous series of n-alkylbenzenes contributes to the establishment of the aforementioned relationships. In the production of ethylbenzene and its homologues, solutions based on n-alkylbenzenes are quite common. Alkylbenzenes are widely used in various fields of science and chemical technology as solvents, extractants, and plasticisers. Using the ebuliometric method, we measured the boiling points of solutions of four binary systems formed by ethylbenzene and n-alkylbenzenes under various pressure values. Compositions of equilibrium vapour phases of the binary systems were calculated using the obtained isotherms of saturated vapour pressure of the solutions. Using the Runge-Kutta method, the composition of the vapour phases of the solutions of the systems was calculated by the numerical integration of the Duhem–Margules equation on a computer. The obtained data on the vapour-liquid equilibrium became the basis for calculating the thermodynamic functions of the systems’ solutions. The Gibbs and Helmholtz energy values, the enthalpies of vaporisation and mixing, the internal energy, and entropy of solutions were calculated. The thermodynamic properties of the solutions were calculated using a comparison of the values baed on two standards: an ideal solution and an ideal gas. It was found that the values of the Helmholtz energy linearly depend on the molar mass of the substance (the number of –CH2– groups in a molecule) in the homologous series of n-alkylbenzenes. An increase in the Helmholtz energy values for n-alkylbenzenes in the homologous series is associated with a linear increase in the molar volume of liquid substances and an exponential decrease in the saturated vapour pressure of substances. For binary solutions of constant molar concentrations formed by ethylbenzene and n-alkylbenzenes, the Helmholtz energy linearly depends on the molar mass (number of –CH2– groups in the molecule) of n-alkylbenzene in the homologous series. We obtained an equation that makes it possible to predict the thermodynamic properties of solutions of binary systems with high accuracy. The equation accelerates the process of studying vapour-liquid phase equilibria and thermodynamic properties of solutions of binary systems by 300 times. The determined patterns confirm the hypothesis of the additive contribution of functional groups to the thermodynamic properties of solutions. This hypothesis underlies the statistical theory of group models of solutions. The thermodynamic patterns determined by this study can also be used to solve a wide range of technological issues in the chemical industry.

Thermodynamic Assessment of the U-Sn System and Extension to the U-Zr-Sn System

Based on the experimental data of phase diagram and thermodynamic properties, the U-Sn system was assessed using the CALculation of PHAse Diagrams (CALPHAD) method. The Redlich-Kister model was used for the description of the liquid phase. A set of self-consistent thermodynamic parameters describing all condensed phases was obtained. The calculated results in this work are in good agreement with available phase equilibria data and thermodynamic data. The tentative U-Zr-Sn ternary system was constructed by extrapolation method and the available ternary experimental data from literature can be reasonably reproduced using the current thermodynamic description.

Thermodynamic description and simulation of solidification microstructures in the Cu–Mg–Zn system

The Cu–Mg–Zn system is one of the important ternary sub-systems in multicomponent light alloys. This ternary system was reassessed in the framework of the CALPHAD method in view of the drawbacks of previous thermodynamic assessments. A critical review of the literature data on phase equilibria and thermodynamic properties has been performed. An updated thermodynamic description for the ternary system is obtained by considering the available literature data. Isothermal and vertical sections, as well as the liquidus surface and the related invariant reactions, are calculated and compared with the corresponding experimental ones. The reaction scheme for the whole ternary system is also presented. The solidification microstructures of several Cu–Mg–Zn alloys along the Mg–Cu0.5Zn0.5 and Mg–Cu0.385Zn0.615 sections were simulated under equilibrium and non-equilibrium conditions. The calculated solidification microstructures do not contradict the experimental ones presented in the literature. This indicates the reliability of the thermodynamic parameters.

The Equilibrium Phase Formation and Thermodynamic Properties of Functional Tellurides in the Ag–Fe–Ge–Te System

Equilibrium phase formations below 600 K in the parts Ag2Te–FeTe2–F1.12Te–Ag2Te and Ag8GeTe6–GeTe–FeTe2–AgFeTe2–Ag8GeTe6 of the Fe–Ag–Ge–Te system were established by the electromotive force (EMF) method. The positions of 3- and 4-phase regions relative to the composition of silver were applied to express the potential reactions involving the AgFeTe2, Ag2FeTe2, and Ag2FeGeTe4 compounds. The equilibrium synthesis of the set of phases was performed inside positive electrodes (PE) of the electrochemical cells: (−)Graphite ‖LE‖ Fast Ag+ conducting solid-electrolyte ‖R[Ag+]‖PE‖ Graphite(+), where LE is the left (negative) electrode, and R[Ag+] is the buffer region for the diffusion of Ag+ ions into the PE. From the observed results, thermodynamic quantities of AgFeTe2, Ag2FeTe2, and Ag2FeGeTe4 were experimentally determined for the first time. The reliability of the division of the Ag2Te–FeTe2–F1.12Te–Ag2Te and Ag8GeTe6–GeTe–FeTe2–AgFeTe2–Ag8GeTe6 phase regions was confirmed by the calculated thermodynamic quantities of AgFeTe2, Ag2FeTe2, and Ag2FeGeTe4 in equilibrium with phases in the adjacent phase regions. Particularly, the calculated Gibbs energies of Ag2FeGeTe4 in two different adjacent 4-phase regions are consistent, which also indicates that it has stoichiometric composition.

In-Class Student Questions and Take-Home Projects for Chemical Engineering Thermodynamics

We present the results of having applied a set of options in thermodynamics courses for encouraging a strong student in-class participation and engagement. Strong emphasis is given to planned ahead in-class student Q&As encompassing both thermodynamics and statistical mechanics and supplemented with take-home extra syllabus reading. Additionally, we designed research-oriented individual and group projects with the goal of promoting critical thinking, problem solving, and both oral and written communication skills. These projects involve quantum chemistry calculations of gas phase thermodynamic properties, solid state equations of state, and optional topics self-selected by the students from a list of provided possibilities. The execution of the Q&As and projects is beneficial and challenging for both the students and the instructor. Our practice demonstrates significant improvement in student’s interest in learning and increased enthusiasm in teaching performance.

Phase diagram, electronic, mechanical and thermodynamic properties of TiB2–ZrB2 solid solutions: A first-principles study

The stability, electronic and phonon structures, mechanical and thermodynamic properties as well optical spectra of the Ti1−xZrxB2 solid solutions were investigated in the framework of a first-principles approach. The miscibility gap was predicted with the consolute temperature TC = 1973 K and composition xC = 0.4. The negative deviation of the calculated bulk, shear, Young moduli, Debye temperature, Vickers hardness and fracture toughness from the mixing rule is observed. The ideal shear stress of 41.1 GPa for Ti0.5Zr0.5B2 was found to be lower compared to that for TiB2 (43.5 GPa) and ZrB2 (43.1 GPa). The calculated elastic moduli and Poisson ratio exhibit the spatial anisotropy inherent to hexagonal structures. It was shown that the thermodynamic characteristics of the Zr-rich solid solutions could be well reproduced in a temperature range up to 1000–1400 K using the harmonic approximation. The calculated dielectric constants εR(ω) and εI(ω), and optical reflectivity spectra R(ω) for Ti1−xZrxB2 were analyzed in comparison with available optical spectra of parent diborides from other authors.

Effect of temperature on phase evolution in Gd2Zr2O7: A potential matrix for nuclear waste immobilization

The dependencies of phase evolution and thermodynamic properties of Gd2Zr2O7 with temperature of preparation have been reported. A series of samples with composition Gd2Zr2O7 have been prepared. The effect of temperature on the phases has been inferred from the powder XRD and Raman spectroscopy. High temperature favors the formation of pyrochlore phase compared to the defect fluorite type phase. The evolution of phase was further quantitatively explained by measuring the formation energy employing high temperature calorimeter. The samples with predominantly pyrochlore phase have higher ΔfH°298 and thermodynamically stable. Also, it is observed that the pyrochlore type phase has larger formation energy compared to fluorite type phase and hence the fluorite to pyrochlore phase transformation is driven by enthalpy. On increasing the annealing temperature more disorder fluorite structure is formed and once the defect concentrations exceed a critical value they order to form the thermodynamically stable pyrochlore structure.