Critical thermodynamic evaluation and optimization of the MgO-Al2O3, CaO-MgO-Al2O3, and MgO-Al2O3-SiO2 Systems

A complete literature review, critical evaluation, and thermodynamic modeling of the phase diagrams and thermodynamic properties of all oxide phases in the MgO-Al₂O₃, CaO-MgO-Al₂O₃, and MgO-Al₂O₃-SiO₂ systems at 1 bar total pressure are presented. Optimized model equations for the thermodynamic properties of all phases are obtained that reproduce all available thermodynamic and phase equilibrium data within experimental error limits from 25 °C to above the liquidus temperatures at all compositions. The database of the model parameters can be used along with software for Gibbs energy minimization to calculate all thermodynamic properties and any type of phase diagram section. The modified quasichemical model was used for the liquid slag phase and sublattice models, based upon the compound energy formalism, were used for the spinel, pyroxene, and monoxide solid solutions. The use of physically reasonable models means that the models can be used to predict thermodynamic properties and phase equilibria in composition and temperature regions where data are not available.     

Thermodynamic optimization of the Na2O-B2O3 pseudo-binary system

The Na₂O-B₂O₃ system is thermodynamically optimized by means of the CALPHAD method. A two-sublattice ionic solution model, (Na⁺¹)_P(O⁻²,BO₃ ⁻³,B₄O₇ ⁻²,B₃O_4.5)_Q, has been used to describe the liquid phase. All the solid phases were treated as stoichiometric compounds. A set of thermodynamic parameters, which can reproduce most experimental data of both phase diagram and thermodynamic properties, was obtained. Comparisons between the calculated results and experimental data are presented.     

Thermodynamic evaluation of phase equilibria in NaNO3-KNO3 system

The binary phase diagram of NaNO₃-KNO₃ was studied by differential scanning calorimetry (DSC) and high-temperature x-ray diffractometry. The solid solutions in the intermediate concentration phase appeared to be a mixture of the NaNO₃-based solid solutions and KNO₃-based solid solutions. This behavior below the solidus suggests that NaNO₃-KNO₃ might well be regarded as a system with limited solid solubilities instead of a continuous series of solid solutions. The temperatures for the solidus and liquidus have been determined with consideration of limited terminal solid solutions. Two models, the Henrian solution and regular solution theory for NaNO₃-based phase and the KNO₃-based phase, respectively, were used to reproduce the solidus and liquidus of the phase diagram. The results are in good agreement with the DSC data. The thermodynamic properties for the NaNO₃-based and KNO₃-based solid solutions have been derived from an optimization procedure using the experimental data. The calculated phase diagram and optimized thermodynamic parameters are thermodynamically self-consistent. Thus, the limited solid solution model seems to be more consistent with the phase diagram obtained by DSC than the continuous solid solution model.     

Thermodynamic reassessment of the BaO-B2O3 system

The BaO-B₂O₃ pseudobinary system is assessed. A two-sublattice ionic solution model, (Ba²⁺) _P (O²⁻, BO ₃ ³⁻ , B₄O ₇ ²⁻ , B₃O_4.5) _Q , is adopted to describe the liquid phase. All the solid phases are treated as stoichiometric compounds. A set of parameters consistent with most of the available experimental data on both phase diagram and thermodynamic properties is obtained by using CALPHAD technique. A comparison between the calculated results and experimental data as well as a previous assessment is presented.     

Critical evaluation and optimization of the thermodynamic properties and phase diagrams of the CrO-Cr2O3-SiO2 and CrO-Cr2O3-SiO2-Al2O3 systems

Available thermodynamic and phase diagram data have been critically assessed for all phases in the CrO-Cr₂O₃-SiO₂ and CrO-Cr₂O₃-SiO₂-Al₂O₃ systems from 298 K to above the liquidus temperatures and for oxygen partial pressures ranging from equilibrium with metallic Cr to equilibrium with air. All reliable data have been simultaneously optimized to obtain one set of model equations for the Gibbs energy of the liquid slag and all solid phases as functions of composition and temperature. The modified quasi-chemical model was used for the slag. The models permit phase equilibria to be calculated for regions of composition, temperature, and oxygen potential where data are not available.     

Experimental and computational investigations on the AlH3/AlF3 system

The possibility of changing the thermodynamic properties of AlH₃, alane, by fluorine anion substitution has been investigated by experimental measurements, ab initio calculations and thermodynamic modelling. No solid solution phases are observed experimentally. In accordance to this the calculations give a positive free energy of mixing for all compositions, showing that a mixed phase is not thermodynamically favourable. Thus fluorine anion substitution does not seem feasible for the alane system.     

Phase Relations in the System CaO-Fe2O3-Y2O3 at 1273?K and Compatibility Between Y1?xCaxFeO3?0.5x and Stabilized Zirconia

Phase relations in the system CaO-Fe₂O₃-Y₂O₃ in air (( P_\textO2 P_{{{\text{O}}_{2} }} /P°) = 0.21) were explored by equilibrating samples representing eleven compositions in the ternary at 1273 K, followed by quenching to room temperature and phase identification using XRD. Limited mutual solubility was observed between YFeO₃ and Ca₂Fe₂O₅. No quaternary oxide was identified. An isothermal section of the phase diagram at 1273 K was constructed from the results. Five three-phase regions and four extended two-phase regions were observed. The extended two-phase regions arise from the limited solid solutions based on the ternary oxides YFeO₃ and Ca₂Fe₂O₅. Activities of CaO, Fe₂O₃ and Y₂O₃ in the three-phase fields were computed using recently measured thermodynamic data on the ternary oxides. The experimental phase diagram is consistent with thermodynamic data. The computed activities of CaO indicate that compositions of CaO-doped YFeO₃ exhibiting good electrical conductivity are not compatible with zirconia-based electrolytes; CaO will react with ZrO₂ to form CaZrO₃.     

Thermodynamic assessment of ZnO-SiO2 system

ZnO-containing slags are common in pyrometallurgical processing of the base metals and steel. This caused the interest to the thermodynamics of the ZnO-SiO₂ system. A complete literature survey, critical evaluation of the available experimental data and a thermodynamic optimization of the phase equilibria and thermodynamic properties of the system ZnO-SiO₂ at 1.013×10⁵ Pa are presented. The molten oxide was described as an associate solution. The properties of liquid were reassessed and enthalpy term of the Gibbs energy of solid Zn₂SiO₄ was re-fitted to be compatible with the new data in the willemite primary phase field. The thermodynamic data set agrees well with the recent experimental observations. It can be used for predicting, e.g., the thermodynamic properties and the domains of the phase diagram, like critical point of the liquid miscibility gap, with a better accuracy than using the previous assessments. A set of optimized model parameters were obtained, reproducing the reliable thermodynamic and phase equilibrium data within their experimental errors from 298 K to liquidus temperatures, over the entire composition range. The created database can be used in a Gibbs energy minimization software to calculate the thermodynamic properties and the phase diagram sections of interest.     

Solubility of YbTe in Sb2Te3 and thermodynamic properties of the solid solution

The solubility of YbTe in Sb₂Te₃ is investigated by a combination of DTA, XRD, SEM, and EMF methods. The fragment of the T-x phase diagram of the YbTe-Sb₂Te₃ system is constructed for 0-25 mol.% YbTe. It is shown that the solubility limit for YbTe in Sb₂Te₃ is achieved at 15 mol.% YbTe at 300 K and at 17.5 mol.% YbTe at 855 K. From the EMF measurements with an YbTe electrode the partial thermodynamic functions of the YbTe pseudo-component are calculated for the alloys of different compositions. Also, the standard integral thermodynamic functions of the YbTe dissolution in Sb₂Te₃ as well as the standard thermodynamic functions of formation and the standard entropy of the solid solution are calculated from the experimental data.     

Thermodynamic analysis of the CsNO3-KNO3-NaNo3 system

The thermodynamic properties of the CsNO₃-KNO₃-NaNO₃ system have been derived from an optimization procedure using experimental and published information concerning phase diagram and thermodynamic data for the constituent binary systems and ternary liquid phase. The results are in very close agreement with the experimental data.     

Critical evaluation and optimization of the thermodynamic properties and phase diagrams of the CrO-Cr2O3, CrO-Cr2O3-Al2O3, and CrO-Cr2O3-CaO systems

Available thermodynamic and phase diagram data have been critically assessed for all phases in the CrO-Cr₂O₃, CrO-Cr₂O₂-Al₂O₃, and CrO-Cr₂O₂-CaO systems from 298 K to above the liquidus temperatures and for oxygen partial pressures ranging from equilibrium with metallic Cr to equilibrium with air in the case of the first two systems and toP _{O 2} = 10⁻³ atm for the CrO-Cr₂O₃-CaO system. All reliable data have been simultaneously optimized to obtain one set of model equations for the Gibbs energy of the liquid slag and all solid phases as functions of composition and temperature. The modified quasichemical model was used for the slag. The models permit phase equilibria to be calculated for regions of composition, temperature, and oxygen potential where data are not available.     

Optimization of thermodynamic properties of the K2O-SiO2 system at high temperatures

An optimized set of thermodynamic functions for the K₂O-SiO₂ system at 10⁵ Pa pressure was obtained by considering available phase diagram and thermodynamic data. KSi_0.25O and SiO₂ were selected as components for the liquid phase. With respect to these components, the highly non-ideal interactions of potassium oxide and silica could be described by using only three temperature-independent Redlich-Kister coefficients for the excess G of the liquid phase. The result is in good agreement with experimental data.     

The quaternary system B2O3-PbO-SiO2-ZnO: Thermodynamics and phase diagram

We evaluated the six binary phase diagrams, B₂O₃-PbO, B₂O₃-SiO₂, B₂O₃-ZnO, PbO-SiO2, PbO-ZnO, and SiO₂-ZnO, to obtain a consistent picture for the quaternary system B₂O₃-PbO-SiO₂-ZnO. We used all the available thermodynamic data: enthalpies of mixing, activity data, complete phase diagrams, and miscibility gaps. The agreement between the various sets of data is good. We also calculated the enthalpy of formation of the ternary compound 5PbO-B₂O₃-SiO₂. Δ_fH/R of 1/8 [5PbO-B₂O₃-SiO₂] =-(2.104 ± 0.057) kK.     

Mechanochemical synthesis of Al2O3-TiB2 nanocomposite powder from Al-TiO2-H3BO3 mixture

Alumina-titanium diboride nanocomposite (Al₂O₃-TiB₂) was produced using mixtures of titanium dioxide, acid boric and pure aluminum as raw materials via mechanochemical process. The phase transformation and structural characterization during mechanochemical process were utilized by X-ray diffractometry (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and thermogravimetric analyses (TG-DTA) techniques. A thermodynamic appraisal showed that the reaction between TiO₂, B₂O₃ and Al is highly exothermic and should be self-sustaining. XRD analyses exhibited that the Al₂O₃-TiB₂ nanocomposite was formed after 1.5 h milling time. The results indicate that increasing milling time up to 40 h had no significant effect other than refining the crystallite size.     

Co_6W_6C化合物的热力学研究

以高纯钨、钴、碳粉为原料,在真空条件下制备获得物相纯净的Co_6W_6C化合物,对Co_6W_6C进行系列实验测定并结合计算得出了其相关的热力学参数。结果表明:在原料粉中碳含量为0.98%~1.06%(质量分数)、真空反应温度为1000℃、保温时间为1 h的条件下,可制备获得物相纯净的Co_6W_6C。结合其等压热容及1173 K下氧化反应的反应焓测定结果,通过计算获得了Co_6W_6C的标准摩尔熵(S_m~Θ)、标准摩尔生成焓(Δ_fH_m~Θ)等热力学参数以及其等压热容(C_p)、焓(H)、熵(S)和吉布斯自由能(G)等基础热力学参量随温度变化的函数关系。     

Thermodynamic study of the CsCl–CeCl3 system by Knudsen effusion mass spectrometry

The vaporization of samples of different chemical and phase compositions covering the complete concentration range of the CsCl–CeCl₃ system was investigated in the temperature range between 749 K and 1098 K by the use of Knudsen effusion mass spectrometry. The gaseous species CsCl, Cs₂Cl₂, CeCl₃, Ce₂Cl₆ and CsCeCl₄ were identified in the vapor and their partial pressures determined. The thermodynamic stability of CsCeCl₄(g) was evaluated by second law treatment of the equilibrium partial pressures. The thermodynamic activities of CsCl and CeCl₃ were obtained at 950 K in the two phase fields {liquid+Cs₃CeCl₆(s)} and {CsCe₂Cl₇(s)+CeCl₃(s)} from the partial pressures of the vapor components. The Gibbs free energies of formation from the constituent halides of the pseudobinary phases Cs₃CeCl₆(s) and CsCe₂Cl₇(s) were evaluated from the thermodynamic activities of the components. The results are discussed with other literature data for the studied system.     

Ab initio study of the structural, thermodynamic and electronic properties of the Cu10In7 intermetallic phase

The physico-chemical properties of the intermetallic phases in the Cu-In system have been a matter of considerable theoretical and experimental interest in connection with, i.a., the application of In-Sn alloys as lead-free micro-soldering alloys. Recently, a new binary compound with the chemical formula Cu₁₀In₇ has been detected in a study of the η-phase field. The structure of the Cu₁₀In₇ phase has been determined as closely related to that of the Cu₁₁In₉ compound occurring in the phase diagram, but no experimental or theoretical information on its electronic structure, thermodynamic and equation-of-state properties has yet been reported. In the present work we report the lattice parameters, bulk modulus, energy of formation from the constituent elements and the electronic structure of the new phase, calculated by applying an ab initio density-functional-theory method. Our calculation technique uses the projector augmented wave potentials and the exchange-correlation functions of Perdew and Wang in the generalized gradient approximation. The present results for the Cu₁₀In₇ phase are compared with the experimental data available, and with the trends in structural and thermodynamic properties emerging from ab initio calculations also performed in the present study for various structurally related and neighboring compounds in the Cu-In phase diagram, viz., the ideal B8₂-Cu₂In, B8₁-CuIn, B8₂-CuIn₂ phases and the Cu₁₁In₉ compound.     

Strain effect on phase transitions of BaTiO3 nanowires

The effects of strain on the phase transitions of BaTiO₃ nanowires taking into account three components of polarization are studied by thermodynamic analysis based on the Landau theory. Similar to the strain effect on phase transitions in thin films, the mismatch strain between the nanowire and substrate governs the Curie temperature. The complete misfit strain–temperature phase diagram shows six stable ferroelectric phases for BaTiO₃ nanowires under different strain and temperature conditions.     

Thermodynamic functions from lattice dynamic of KMgH3 for hydrogen storage applications

The dynamic and the thermodynamic properties of KMgH₃ have been investigated by density functional theory (DFT). We have found that the calculated lattice parameters differ from the experimental data by less than 0.6% and the electronic density of states (DOS) reveals that the KMgH₃ is an insulator. The formation energy of KMgH₃ from binary hydrides (MgH₂ and KH) has been calculated. Using density-functional perturbation theory, we have calculated the phonon dispersion curves, the phonon density of states, the Born effective charge tensors, the dielectric permittivity tensors and the phonon frequencies at the center of the Brillouin zone of KMgH₃. Also we have assigned the calculated phonon frequencies at the gamma point for Infrared-active and Raman-active modes. For the first time, the thermodynamic functions are computed using the phonon density of states.