Journal of Phase Equilibria and Diffusion最新文献

Vaporisation studies were carried out over the solid region of LiCl(cr), KCl(cr) and liquid region of LiCl-KCl-UCl₃ ternary salt system by using Knudsen Effusion Mass Spectrometry (KEMS) in the temperature range of 715–913 K. Monomeric and dimeric species were observed in the vapour phase in equilibrium with their respective salts, LiCl(cr) and KCl(cr). LiCl(g), Li₂Cl₂(g), KCl(g), K₂Cl₂(g), and UCl₃(g) were the neutral species observed in the equilibrium vapour over ternary salt. Partial pressure–temperature relations for vapour species were derived using in-situ calibration from pressure dependent equilibrium constants as well as using pure silver as external calibrant. Using p-T relations, various heterogeneous reaction equilibria that exist between condensed phase-gas phase and the dissociation equilibra of following gas phase reactions: Li₂Cl₂(g) = 2LiCl(g); K₂Cl₂(g) = 2KCl(g) were evaluated by using 2nd and 3rd law methods. Also, the enthalpies of pressure-independent reactions: LiCl(cr) + LiCl(g) = Li₂Cl₂(g); KCl(cr) + KCl(g) = K₂Cl₂(g) were evaluated by using 3rd law method. Knudsen effusion mass spectrometric studies on LiCl-KCl-UCl₃ ternary salt system were carried out for the first time.

Sb₂Te₃ is an important thermoelectric material. Co is a potential diffusion barrier. This study examined the electroplated Co/Sb₂Te₃ interfacial reactions at 300  °C, 400 °C and 500 °C. To provide fundamental information and for better understanding the reaction paths, the Co-Sb-Te phase equilibria isothermal sections at these three temperatures are proposed. No ternary compound is found. The 400 °C isothermal section contains (Co), (Sb), (Te), β-CoSb, β-Co_1−xTe, CoSb₃, δ-(Sb₂Te), γ-(SbTe), Sb₂Te₃ and a continuous solid solution γ-Co(Sb,Te)₂. At 500 °C, except for Te being molten, the phase relationships are similar to those at 400 °C. At 300 °C, although γ-CoSb₂ and γ-CoTe₂ have very significant mutual solubilities, they are two separate phases and do not form a continuous solid solution. In the Co/Sb₂Te₃ couple reacted at 300 °C, only one reaction phase, γ-CoTe₂ with Sb solubility, is formed. Similar results are found in the Co/Sb₂Te₃ couple reacted 400 °C, and the reaction phase is the continuous solid solution γ-Co(Sb,Te)₂. Two reaction phases, β-Co_1-xTe and γ-Co(Sb,Te)₂, are found in the couple reacted at 500 °C. The compositional ratio of Sb/Te in the reaction phase remained at 2/3 indicates that Co is the dominating diffusion species. The reaction phases are formed rapidly by Co penetration into the Sb₂Te₃ substrate. A peculiar phenomenon was found with the reaction layer that formed on the side of Co that was not in direct contact with the Sb₂Te₃ substrate which will be further investigated.

Thermodynamic databases are essential to understanding alloy properties and guiding materials design. In this work, the mixing enthalpies of the liquid phase in the Gd-Te, Dy-Te and Ho-Te binary systems are calculated using Ab-initio Molecular Dynamics (AIMD) simulations and the thermodynamic parameters are determined using the CALculation of PHAse Diagrams (CALPHAD) method combined with the phase equilibrium data and thermodynamic data. The associated solution model is employed to describe the liquid phase of these systems. The sublattice model (Gd,Te)_0.0296(Gd)_0.4(Te)_0.5714, (Dy,Te)_0.0286(Dy)_0.4286(Te)_0.5714 and (Ho,Te)_0.5(Te)_0.5 are utilized to describe Gd₂Te₃, Dy₂Te₃ and HoTe, respectively. The line compounds, i.e. GdTe, DyTe, and DyTe₂, are modeled using the stoichiometric model. The calculated results can describe the experimental and thermodynamic information reported in the literature. In addition, the existence of a liquid-liquid separation in the Dy-rich side in the Dy-Te binary system is proposed in this work.

The parallel tangent method widely applied to predict the composition and driving force to form a nucleus from an oversaturated solution is extended in this paper. The parallel tangent method is shown to (i) Over-estimates the composition difference between the first nucleus and the parent phase, (ii) Neglects the composition dependence of interfacial energies and (iii) Neglects the composition dependence of probability to form embryos prior to nucleation. New model equations are developed here for the composition dependence of the interfacial energies and probability to form the embryos as function of nucleus composition at given matrix composition. The most probable composition of the first nucleus is found at the maximum of the driving force of nucleation extended by the new model equations. The success of the extended method is demonstrated for an Al-Fe liquid alloy with 0.3 w% of Fe to predict the first nucleating intermetallic phases upon cooling after nucleation of the fcc phase. It is shown that although the prediction based on the parallel tangent method contradicts experimental observations, the prediction based on our extended method agrees with them.

Graphical Abstract

The aim this work was the reinvestigation of phase equilibria in Bi-Te system. The as-cast and long-time equilibrated alloys of Bi-Te binary system were analysed by scanning electron microscopy, X-ray diffraction (XRD) and differential thermal analysis (DTA) methods. The primary solidified phases were identified for as-cast samples. The existence of the four intermetallic phases: Bi₂Te₃, BiTe, Bi₂Te, Bi₇Te₃ was confirmed. Three of them melt incongruently in peritectic reactions. The model parameters of all phases in this system were assessed by optimization using available data by Calphad method. The stabilisation of these phases in other ternary systems was discussed taking into consideration its future application in thermodynamic description of Ag-Bi-Te ternary system.

Zr metal bulks were isothermally reacted with B powder at 800-1630 °C for 2-16 h to form ZrB₂ layers on the Zr bulk surfaces. Diffusion kinetics of B element in association with Zr + B solid state reaction was investigated by means of XRD, SEM and EDS. Nano-sized ZrB₂ grains without formation of a discernible layer were detected on the Zr surface after reaction at 800 °C for 2 h. When the reaction temperature was increased, continuous layers consisting of faceted ZrB₂ grains were formed at temperatures ranging from 1200 to 1500 °C. The thickness of the ZrB₂ product layers showed a parabolic dependence on time t and an exponential dependence on temperature T via − 1/RT. The Zr + B reaction calculated a diffusion activation energy G = 152.0 ± 62.4 kJ/mol for B diffusion in ZrB₂. The diffusion coefficient of B element was experimentally determined to be (D{ } = 1743.4 times 10^{ - 12} {text{ exp}}left( {{raise0.7exhbox{${ - 152027.6}$} !mathord{left/ {vphantom {{ - 152027.6} {{text{R}}T}}}right.kern-0pt} !lower0.7exhbox{${{text{R}}T}$}}} right)).

The diffusion couples of Ni-Ti-V ternary alloys prepared and annealed at 1373 and 1473 K have been measured by electronic-probe microanalysis. Based on the concentration profiles, the interdiffusion coefficients were determined by using the Whittle and Green method. The atomic mobilities of the Ni-Ti-V ternary alloys were assessed based on the interdiffusion coefficients reported in the literature and the data obtained from the present work. In the comprehensive comparison, it was found that the model-predicted diffusion properties were in good agreement with the experimental data, which indicated that the diffusion phenomena such as diffusion paths and concentration profiles in the Ni-Ti-V ternary system can be reasonably described by the obtained atomic mobilities. This work contributes to the establishment of nickel-based kinetic database.

Phase equilibria in the Hf–Rh–Ir system at subsolidus temperatures (about 20-50 °C below solidus temperatures) were studied using optical microscopy, scanning electron microscopy, electron probe microanalysis, differential thermal analysis, x-ray diffraction and solidus temperature measurements (Pirani-Althertum technique). For the first time it was established that the solid solution based on βHf, continuous series of solid solutions between isostructural (Cu-type) components iridium and rhodium, isostructural compounds Hf₂Rh and Hf₂Ir (Ti₂Ni-type), high-temperature modifications of HfRh and HfIr (CsCl-type), HfRh₃ and HfIr₃ (AuCu₃-type), as well as solid solutions based on the compounds Hf₅Ir₃ and Hf₃Rh₅ take part in phase equilibria. Solidus surface of this system is formed by seven single-phase surfaces corresponding to solid solutions based on components and above-mentioned compounds, eight tie-line surfaces limiting the two-phase volumes, and two isothermal planes corresponding to invariant four-phase equilibria with participation of the liquid phase (at 1958 and 1655 °C).

The present works assesses the knowledge concerning the crystal structures of phases in the Cu–Sn system having their high relevance due to their occurrence in bronze alloys and soldered systems. The crystal structures of the terminal solid solution phases α-Cu and β-Sn and of the stable main intermediate phases β, γ, ε-Cu₃Sn, δ-Cu₄₁Sn₁₁, ζ-Cu₁₀Sn₃, η-Cu₆Sn₅ and η′-Cu₆Sn₅ and some metastable phases appear to be well established in the literature, but details can be intriguing. This paper attempts to review apparently or truly contradictory structure models derived from experimental diffraction data for the different phases, revealing limiting knowledge in some cases. These results are also analyzed regarding the results of first-principles calculations making use of various model structures. The review is also used to highlight exemplarily problems, which can be experienced upon widespread, “routine” means of phase identification, in particular x-ray diffraction (on polycrystalline specimens) and electron backscatter diffraction.

The phase equilibria of the Ce-Co-Zr ternary system at 873 and 1073 K were determined for the first time by using equilibrated alloys in combination with scanning electron microscopy with energy dispersive spectroscopy and x-ray diffraction. No stable ternary intermetallic compounds were detected in the Ce-Co-Zr ternary system. Due to the partial substitution of Ce by Zr, the metastable binary intermetallic compound CeCo₇ with a solubility of 3.3 at.% Zr is stabilized at 873 K. The experimental results demonstrate that the maximum solubilities of Zr in the intermetallic compounds Ce₂Co₁₇, CeCo₅, Ce₅Co₁₉, Ce₂Co₇, CeCo₃, and CeCo₂ at 873 K are 4.3, 2.6, 2.4, 9.0, 17.9, 3.5 at.%, respectively, while the maximum solubilities of Ce in the intermetallic compounds Co₂₃Zr₆, Co₂Zr, and CoZr₂ are 6.7, 1.7, and 2.3 at.%. Meanwhile, the maximum solubilities of Zr in Ce₂Co₁₇, CeCo₅, Ce₅Co₁₉, Ce₂Co₇, CeCo₃ and CeCo₂ at 1073 K were measured to be 4.0, 7.5, 1.9, 6.8, 17.1, and 9.1 at.%, respectively, while the maximum solubilities of Ce in the intermetallic compounds Co₂₃Zr₆ and Co₂Zr were determined to be 7.0 and 4.5 at.%, respectively. Finally, the isothermal sections of the Ce-Co-Zr ternary system at 873 and 1073 K were established in this work.