Thermodynamic Evaluation of Yttrium

ＴｈｅｒｍｏｄｙｎａｍｉｃＥｖａｌｕａｔｉｏｎｏｆＹｔｔｒｉｕｍＳｈｅｎＨｕａｓｅｎ，ＺｈａｎｇＷｅｉｊｉｎｇ，ＬｉｕＧｕｏｑｕａｎ，ＷａｎｇＲｕｎａｎｄＤｕＺｈｅｎｍｉｎ（沈化森）（张维敬）（刘国权）（王润）（杜镇民）（ＤｅｐａｒｔｍｅｎｔｏｆＭａ...     

Interface thermodynamics of nano-sized crystalline,amorphous and liquid metallic systems

Expressions for the Gibbs energies of interfaces occurring in particular for solid and/or liquid/amorphous metals or alloys in contact with each other have been developed. To consider its energetics, an amorphous alloy has been modelled as a mixture of the undercooled liquid metal components near to the glass transition temperature making use of the enthalpy of melting, the entropy of melting and the temperature-dependent contribution of the heat capacity of the undercooled melt. Gibbs surface and interface energies have been obtained on the basis of the “macroscopic atom” Miedema model, where the entropy contributions of alloys have been derived applying a recently developed formalism. The Gibbs energy of a crystalline interface phase has been formulated. The molar fractions of the components of the alloy at the surfaces have been determined by minimising the surface energy. These results provide a thermodynamic basis for unusual phenomena observed in nano-sized systems. The formalism has been applied to calculate the thermodynamic stability of interface phases in a nano-sized, multi-layered system of iron and zirconium and to explain the aluminium-induced crystallisation of amorphous silicon and the layer exchange occurring in bi-layers of crystalline aluminium and amorphous silicon.     

Enthalpy increment measurements of PbI2: evidence for a reversible polytypic transition

The enthalpy increment of solid and liquid PbI₂ have been measured by drop calorimetry from 528 to 763 K and the X-ray diffraction pattern has been recorded from 300 to 633 K. The calorimetric data show evidence for a reversible transition at 580 K, the enthalpy difference between the two phases being small, 339 J mol⁻¹. The X-ray diffraction results show a transition of the 2H to the 4H polytype at 440 K, for which the reverse reaction is not observed. The melting point of PbI₂ has been found at (679 ± 1) K by DSC, the enthalpy of fusion was obtained as Δ_fusH° = 23471 J mol⁻¹ from the enthalpy increments of the solid and liquid phase.     

High Temperature Thermodynamic Data for CdTe(c)

The high temperature heat capacity, Gibbs energy of formation, and standard enthalpy and entropy of formation at 298 K are combined with thermodynamic data for Cd and revised data for Te to provide an internally consistent data set for CdTe(c). Equations are given for the Gibbs energy of formation from Cd(g) and Te₂(g) and from the solid or liquid elements as a function of temperature. These give values similar to those used before. However, the derived enthalpy and entropy of formation are significantly different due to a revised heat capacity for CdTe(c). The standard enthalpy and entropy of formation at 298.15 K from the gases are −293262 J/mol and −200.593 J/mol K, respectively. From the solid elements they are −100270 and −4.5334.     

Thermodynamic properties of 1-nutyl-3-methylimidazolium chloride (C<Subscript>4</Subscript>mim[Cl]) ionic liquid

Thermodynamic properties of 1-butyl-3-methylimidazolium chloride (C₄mim[Cl]) ionic liquid were determined using thermogravimetric (TG) differential thermal analysis (DTA). A new method called DTA mass-difference baseline, was used to measure the heat capacity and enthalpy change of phase transformation of ionic liquid from DTA curves. Based on this, the changes in standard enthalpy, entropy, and Gibbs energy were determined. The results show that standard enthalpy and entropy changes of C₄mim[Cl] increase nonlinearly with increasing temperature, while the standard Gibbs energy change decreases nonlinearly with increasing temperature within the temperature range studied (298–453 K). The standard enthalpy of melting and enthalpy of vaporization were determined to be 0.93 and 11.07 kJ/mol, respectively.     

Reevaluation of the Fe-Mn phase diagram

New results for the enthalpy of mixing of liquid Fe-Mn alloys, the enthalpy of formation of γ-Fe-Mn solid solutions and the heat capacity of α-Fe-Mn and γ-Fe-Mn alloys obtained by isoperibolic calorimetry and differential thermal analysis (DTA) measurements have been used for the reassessment of the molar Gibbs energy of the various phases of the Fe-Mn system. Experimental information about martensitic transformation temperatures in Fe-Mn alloys published recently was incorporated in the updating of the occurring metastable equilibria. The present reevaluation results in a good fit with all available experimental data and is compared with the results of previous assessments.     

Critical Systematic Evaluation and Thermodynamic Optimization of the Fe-RE System: RE = Gd,Tb, Dy,Ho, Er,Tm, Lu,and Y

As the second part of the thermodynamic study of binary Fe-RE system, critical evaluations and optimizations of all available phase diagrams and thermodynamic data for the Fe-heavy RE (heavy RE = Gd, Tb, Dy, Ho, Er, Tm, Lu, and Y) systems were conducted to obtain reliable thermodynamic functions of all the phases in the systems. In the thermodynamic modeling of the heavy RE systems, systematic variations in the phase diagrams and thermodynamic properties such as the enthalpy of mixing in the liquid state and enthalpy of formation of solid compounds with the atomic number of lanthanide series were observed. These systematic trends were incorporated in the optimization of the Fe-heavy RE system to resolve inconsistencies between available experimental data and to estimate unknown thermodynamic properties. The systematic trends in thermodynamic properties of solid and liquid phases and phase diagram of the entire Fe-RE systems were summarized.     

On the interfacial energy of coherent interfaces

A thermodynamic model has been developed for interfacial energies of coherent interfaces using only the molar Gibbs energy and the molar volume of the two phases surrounding the interface as the initial data. The analysis is started from the simplest case of the interface formed by two solutions on the two sides of a miscibility gap, when both phases are described by the same Gibbs energy and molar volume functions. This method is applied to the fcc Au–Ni, liquid Ga–Pb and liquid Al–Bi systems. Reasonable agreement was found with the measured values in liquid Ga–Pb and Al–Bi systems. It was shown that the calculated results are sensitive to the choice of the Calphad-estimated thermodynamic data. The method is extended to the case where the two phases are described by different Gibbs energy and molar volume functions. The extended model is applied to the interface present in an Ni-based superalloy between the AlNi₃ face-centered cubic (fcc) compound and the Ni–Al fcc disordered solid solution. The calculated results are found to be similar to other values recently obtained from the combination of kinetic and thermodynamic data. The method is extended to ternary and higher order systems. It is predicted that the interfacial energy will gradually decrease with the increase in number of components in the system.     

The thermochemistry of transition metal sulfides

A survey is made of the available data for the standard Gibbs energies of formation of solid and liquid sulfides of transition metals. The results are plotted as standard Gibbs energy vs temperature diagrams. The equations and estimated accuracy are quoted for each substance.Supported by a Glunz Fellowship from the Ohio State University.     

Thermodynamic optimisation of the Pb–Tl binary system

The phase diagram of the Pb–Tl binary system is experimentally well determined. Experimental thermodynamic values for all the phases involved are also available. For the liquid phase the temperature dependence of the enthalpy of mixing is also determined. In the present contribution, a consistent set of Gibbs energy functions of all the phases is obtained using the Redlich–Kister polynomial. The adjustable model parameters were determined by least-squares fit to the experimental data. A satisfactory agreement between experimental and calculated values is observed.     

Thermodynamic modeling of the Fe-S system

A thorough review and critical evaluation of phase equilibria and thermodynamic data for all phases in the iron-sulfur (Fe-S) binary system at 1 bar pressure has been made over the entire composition range for temperatures from 25 °C to above the liquidus. The Gibbs energies of ten phases have been modeled, and optimized model parameters have been obtained that reproduce all data simultaneously within experimental error limits. For the liquid phase, the recently extended modified quasi-chemical model is applied for the first time to a liquid metal-sulfur phase. A two-sublattice model within the framework of the compound energy formalism is used for the high-temperature monosulfide pyrrhotite solution. A substitutional model is used for the dissolution of S in solid iron. The Gibbs energies of six stoichiometric compounds are also modeled.     

Thermodynamics of La based La–Al–Cu–Ni–Co alloys studied by temperature modulated DSC

The onset and offset melting temperatures T_m and T_l, glass transition temperature T_g and heat of fusion ΔH_m of six La based La–Al–Cu–Ni–(Co) alloys were measured by DTA or DSC at a heating rate of 20 K/s. The absolute values of specific heat capacity for the undercooled liquid and the corresponding crystalline of these six alloys were obtained by means of temperature-modulated DSC (TMDSC). Entropy, enthalpy and Gibbs free energy differences between the undercooled liquid and crystalline of these alloys as a function of temperature have been calculated. Their glass forming ability was discussed from a thermodynamic point of view.     

Phase diagram of Fe-Cu-Si ternary system above 1523 K

Fe-Cu-Si ternary alloy phases are commonly formed during melting in a treatment process of domestic waste incineration that is currently being developed. The alloy phases appear in the incineration residue. Experiments were performed to observe phase equilibria in solid Fe+liquid, solid Si+liquid, the compound of FeSi liquid, and so forth, in the range 1523 to 1723 K. Then the phase diagram of Fe-Cu-Si ternary was thermodynamically assessed based on the present experimental results and literature data. It was found that this system has a wide liquid miscibility gap, and this two-liquid region is stable up to about 1900 K. The phase diagram of Fe-Cu-Si system assessed in the present work is much different from an earlier proposed diagram, but is very close to one recently evaluated. From the results obtained, the appropriate condition is discussed for the operation of the melting furnace for ash from municipal solid waste incinerators.     

Thermodynamic analysis of the simple microstructure of AlCrFeNiCu high-entropy alloy with multi-principal elements

AlCrFeNiCu high-entropy alloy (THA) was synthesized by the arc melting and casting method. The alloy exhibits simple FCC and BCC solid solution phases rather than intermetallic compounds. The reason is that the Gibbs free energy of mixing of the equimolar A1CrFeNiCu alloy is smaller than that of inter-metallic compounds by calculation according to the Miedema model.     

Analysis of the Zn-Se system

The Zn-Se phase diagram is reanalyzed with an associated solution model for the liquid, new Se-rich liquidus points, and a new Gibbs energy of formation for ZnSe(s). After the liquid model parameters are fixed by a best fit to the liquidus points, the entire liquidus is generated as well as the partial pressures of Zn and of Se₂ along the ZnSe(s) three-phase curve, isotherms for the enthalpy of mixing, and the isotherm for the activity coefficients at the 1799 K melting point of ZnSe(s).     

Analysis of the Zn-Se system

The Zn-Se phase diagram is reanalyzed with an associated solution model for the liquid, new Se-rich liquidus points, and a new Gibbs energy of formation for ZnSe(s). After the liquid model parameters are fixed by a best fit to the liquidus points, the entire liquidus is generated as well as the partial pressures of Zn and of Se₂ along the ZnSe(s) three-phase curve, isotherms for the enthalpy of mixing, and the isotherm for the activity coefficients at the 1799 K melting point of ZnSe(s).