Thermodynamic and ab initio investigation of the Al–H–Mg system

A coupled ab initio and thermodynamic study of the Al–H–Mg system has been carried out and a self-consistent thermodynamic database has been obtained. Magnesium alanate Mg(AlH₄)₂, a candidate material for hydrogen storage, has been included into the database. According to Density Functional first principles calculations, the alanate is an insulator and its thermodynamic properties have been obtained at room temperature. This compound has been found metastable at 298.15 K and 1 bar. The alanate has been found thermodynamically stable only at high pressure when the formation of the binary β-MgH₂ phase is neglected. A reassessment of thermodynamic parameters of the liquid phase in the binary Mg–H system has also been carried out in order to be consistent with the Al–H system. The present results can reproduce reasonably well the available experimental data.     

Experimental study and thermodynamic modelling of the ZrO2–LaO1.5 system

Phase relations in the ZrO₂–LaO_1.5 system were studied experimentally in the temperature range from 1673 to 1973 K. X-ray diffraction and scanning electron microscopy were employed to obtain the structural information and the compositions of the tetragonal and pyrochlore (La₂Zr₂O₇) phases. The solubility of LaO_1.5 in the tetragonal phase was determined to be very small. The homogeneity range of the pyrochlore phase is estimated to be less than 2 mol% at 1973 K, and less than 1 mol% at 1673 K according to the present work. Based on the experimental results obtained in this work, as well as the available phase diagram and thermodynamic data in literature, a self-consistent thermodynamic assessment was carried out by using the ionic sublattice solution model.     

Thermodynamic optimization of the Ni–Sn binary system

Through the CALPHAD method and based on experimental data of thermodynamic properties and phase boundaries, the phase diagram of the Ni–Sn binary system has been reassessed. The liquid and fcc_A1 (terminal rich nickel solid solution) phases were described by using a simple substitutional model, the excess Gibbs energy being formulated with a Redlich–Kister expression. The other intermediate phases (Ni₃Sn_HT, Ni₃Sn₂_HT, Ni₃Sn₂_LT, Ni₃Sn₄), were described with a several sublattice model with different formula; the Gibbs energy of the reference compounds was assumed to be linear, and the binary interaction terms on the sub-lattices to be constant. Ni₃Sn_LT was treated as a stoichiometric compound. The solubility of Ni in the terminal phase bct_A5(Sn) was neglected because it is very small. Finally a set of self-consistent thermodynamic parameters for all condensed phases in the Ni–Sn binary system was obtained, which can reproduce most of the experimental data.     

Thermodynamic assessment of the Si–N system

Motivated by the thermodynamic assessment of the Ga–N and In–N binaries, the thermodynamic parameters of the Si–N system are optimized in a similar way. The intermetallic compound Si₃N₄ is treated as stoichiometric and the terminal solution phase diamond_Si as the pure diamond_Si. The liquid solution phase is assumed to be a substitutional solution with Redlich–Kister formula for the expression of its excess Gibbs energy. The fugacity of nitrogen is considered when describing the behavior of the gas phase, especially with high pressure. The complete T–x phase diagram for the Si–N binary system is given. In this optimization a consistent thermodynamic data set for the Si–N system is obtained by means of CALPHAD (CALculation of PHAse Diagrams) method. The calculation results agree well with experiments.     

Critical thermodynamic evaluation of oxide systems relevant to fuel ashes and slags. Part 3: Silica–alumina system

The Al₂O₃–SiO₂ system was reassessed using the associate species model for the liquid and the sublattice and associate species model for the mullite. The available phase diagram data were collected and evaluated for the purpose of improving the solution database. The new data for the liquid phase and mullite are compatible with data for the pure stoichiometric component oxides from the FACT Pure Substance database. The phase equilibria re-calculated using the improved solution data are in good agreement with experimental data. This work continues the studies concerning the thermodynamic assessment of oxide systems relevant to ashes and slags.     

Thermodynamic study of the KCl-K2SO4-K2Cr2O7-H2O system at the temperature 298.15 K

The Pitzerion-interaction model has been used for thermodynamic simulation of the ternary solutions KCl-K₂Cr₂O₇-H₂O, KBr-K₂Cr₂O₇-H₂O and K₂SO₄-K₂Cr₂O₇-H₂O and the quaternary system KCl-K₂SO₄-K₂Cr₂O₇-H₂O at T=298.15 K. The necessary thermodynamic functions (binary and ternary parameters of interionic interaction and thermodynamic solubility products) have been calculated and the theoretical solubility isotherms have been plotted. Good agreement between experimentally determined and calculated solubilities has been found.     

Experimental study and thermodynamic assessment of the Ag–Ti system

A thermodynamic assessment of the binary Ag–Ti system was performed based on the evaluation of the literature and the results of the present experiments. For the experimental study, special deep embedding diffusion couples were prepared and analyzed by scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). The phase equilibrium relationship and the conjugate phase compositions were determined at 1023 K, 1253 K, 1373 K and 1474 K respectively. For the thermodynamic assessment, the Redlich–Kister polynomial was used to describe the solution phases, liquid (L), bcc, hcp, and fcc. The sublattice-compound energy model was employed to describe the intermediate phase, (AgTi), with a homogeneity range. The other intermediate phase, AgTi₂, without a homogeneity range was treated as the stoichiometric phase. A set of self-consistent thermodynamic parameters of the Ag–Ti system has been obtained. The calculated phase diagram was presented and compared with the experimental data.     

Thermodynamic Study of the Chemical Vapour Deposition in the Si---B---C---H---Cl System

This paper presents the results of a thermodynamic study concerning the codeposition of phases of the silicon, boron and carbon system by a classical C.V.D. technique from an initial gaseous mixture composed of methyltrichlorosilane (MTS), boron trichloride (BCl₃) and hydrogen. The thermodynamic approach developed here is specific in the sense that for the first time the non-stoichiometry of boron carbide is described from B₄C up to B₁₀C. The Gibbs' energy of the solid solution phase is assumed to follow the sublattice model.

A deposition diagram is determined as a function of the initial gas composition together with the equilibrium yields of the different gaseous and solid species. Finally, an interesting deposition domain could be chosen for future experiments of deposition on C/C, C/SiC and SiC/SiC composites.     

Thermodynamic phase diagram analysis of three binary systems shared by five neopentane derivatives

A thermodynamic analysis was made of the solid-plastic and plastic-liquid equilibria of three binary systems in which the components are plastic crystals. These substances are neopentane derivatives: neopentylglycol (NPG), pentaglycerin (PG), 2-amino-2-methyl 1, 3-propanediol (AMP), tris(hydroxymethyl)aminomethane (TRIS) and 2-methyl 2-nitro 1-propanol (MNP). Each of the three systems, which are PG/MNP, NPG/MNP and TRIS/AMP, show a plastic-liquid loop and a solid-plastic phase diagram of the eutectoid type. One of them, i.e. PG/MNP, is an example of crossed isodimorphism: two solid-plastic loops crossing each other giving rise to a three-phase equilibrium.

In the thermodynamic analysis the liquid mixtures were taken as ideal mixtures and for the plastic crystalline mixtures the (A, B, ) model was used to express the excess thermodynamic functions. In this analysis, phase diagram data and experimental enthalpies of melting were used.     

Thermodynamics and phase diagram of the binary system Bi2O3-B2O3

We analyzed the thermodynamic data of the binary system Bi₂O₃-B₂O₃. The phase diagram contains five compounds, of which four melt congruently, and a miscibility gap, close to pure B₂O₃. The three sets of transformation data of Bi₂O₃, the enthalpy of mixing data in the liquid, and the critical point of the miscibility gap gave five equations for the excess Gibbs energy of mixing and five sets of values for the enthalpies of formation of the binary compounds. The critical point data yielded another set of transformation data for Bi₂O₃. Using the monotectic composition and the enthalpy of mixing data also yielded a set of transformation data for Bi₂O₃. The values obtained using the enthalpy of mixing data are the most reliable values.