Journal of Phase Equilibria and Diffusion最新文献

There exists strong experimental evidence that bainitic ferrite is formed as a supersaturated solid solution of carbon within a tetragonally-distorted body-centered iron structure (BCT), where carbon preferentially occupies the octahedral site. Despite this, the BCT structure has not yet been accounted for in the computational analysis of the thermodynamics of the bainite transformation. In the present work, we propose to calculate the onset of the bainite transformation based on the T₀′ concept, including the effect of Zener-ordering. This mechanism stabilizes the BCT structure, makes it energetically more favorable than BCC and leads to a significantly higher solubility of C compared Fe-BCC. The computational predictions are made based on a recent reassessment of low-T Gibbs energies and finally compared to experiments. The important role of C is emphasized, with the Fe-C system used as a showcase.

The quasi-ternary system Cu₂Se-In₂Se₃-CuI has been investigated by x-ray diffraction and differential thermal analysis. The isothermal section at 770 K and the liquidus surface projection of the system have been built. For the first time, the primary crystallization regions, and the coordinates of the invariant and monovariant equilibria have been determined. In the system, the regions of the solid solutions based on the binary, ternary, and quaternary compounds have been investigated. The formation of the CuIn₂Se₃I quaternary compound, which melts congruently at 1213 K and has a homogeneity region of 15 and 9 mol.% CuI within the composition triangle has been established. For the first time, the crystal structures of CuGa₂Te₃I and AgGa₂Te₃Br compounds have been studied using a powder method. They crystallize in the tetragonal symmetry, Space Group I-4, a = 5.9147(4) Å, c = 11.952(2) Å for CuGa₂Te₃I; a = 6.2977(3) Å, c = 11.9473(7) Å for AgGa₂Te₃Br compound, respectively. The connection of their structures with the structures of the defective diamond-like semiconductors has been discussed.

The paper proposes a method based on a combination of the provisions of the phonon theory of liquid, V–T formalism, and Frenkel’s theory of determining the P–T parameters of a liquid system, to determine the pressure and temperature values at which the transition from a denser liquid fraction to a less dense one occurs. Its use makes it possible to analyze the motion of fluid components in joint complexes and to determine their lifetime. It is also shown that at short time intervals, regardless of the physical state of the system, the components of the liquid move as independent particles, and their motion can be represented within the framework of the vibrational-hopping diffusion model. In this paper, the developed methodology is used to study the structural and dynamic properties of argon near the triple point on the liquid–gas coexistence curve.

The doping with Cu in the Sb-Se material system can effectively reduce power consumption and improve data retention ability of the PCRAM (Phase-Change Random-Access Memory) material. However, no thermodynamic study of the Cu-Sb-Se system has been reported. Therefore, in this work the Cu-Sb-Se system was modeled using the CALPHAD (CALculation of PHAse Diagrams) method. The excess Gibbs energies of solution phases, including liquid and FCC were expressed by the Redlich-Kister polynomial. Two-sublattice model (Cu,Se)₂Se was used to describe the solid solution of binary intermetallic compounds, i.e. α-Cu₂Se and β-Cu₂Se in Cu-Sb-Se ternary system. The compounds, e.g. η(Cu₂Sb), β(Cu₃Sb), Sb₂Se₃, α-CuSe, β-CuSe, Pe(Cu₃SbSe₄) and C(CuSb₃Se₅) were described as stoichiometric compounds. The temperature of the eutectic reaction γ(Cu₁₇Sb₃) = (Cu) + δ(Cu₄Sb) in the Cu-Sb system and the temperature of the invariant reaction L1 = L2 + (Sb) in the Sb-Se system were adjusted. A set of self-consistent thermodynamic parameters for the Cu-Sb-Se system was obtained, and the 623, 673, 723, 773, 873 and 973 K isothermal sections, and the liquidus projection and invariant reactions for this ternary system have been calculated.

In this study, the phase equilibria of the Nb-V-Hf ternary system at 1300, 1100 and 1000 °C were experimentally investigated by means of back-scattered electron imaging, electron probe microanalysis, and x-ray diffraction. The results show that one ternary Laves compound with a hexagonal C14 structure is found in the isothermal sections that were studied. The bcc phase forms a large continuous solid solution, and no phase separation occurs at 1000 °C as had been claimed in the literature. As the temperature rises from 1000 to 1300 °C, the bcc structure can be observed in the Hf-V side, and the phase region of C15 reduces.

The solubility values of eight common alloying elements Al, Ca, Ce, Gd, Nd, Sn, Y and Zn in hcp Mg are experimentally measured from diffusion profiles obtained from diffusion multiples and liquid-solid diffusion couples (LSDCs) using electron probe microanalysis. These solubility values are used to stablish solidus and solvus lines and compared with the experimental results reported in the literature as well as the computed phase boundaries using two CALPHAD (CALculation of PHAse Diagrams) databases. Our experimental values for Mg-Ca (530, 580, 600, 630 °C), Mg-Ce (605, 630 °C), Mg-Gd (570, 600, 630 °C) and Mg-Nd (615, 630 °C) are the first ever measurements of the hcp solidus for these four binary systems. Additional solubility data obtained from our experiments are reported for Mg-Al (375, 420, 450, 500, 550, 600 °C), Mg-Sn (375, 420, 500, 550, 600 °C), Mg-Y (590, 610, 630 °C), and Mg-Zn (275, 450, 500, 550 °C). Our experimental data are valuable input to future thermodynamic reassessments of the eight binary systems. This study also clearly shows the effectiveness of measuring solidus data using the elegant LSDCs.

The LiCl-KCl-GdCl₃ quasi-ternary phase diagram has been investigated by differential thermal analysis (DTA) and x-ray diffraction (XRD) techniques. These experiments showed that the LiCl-KCl-GdCl₃ system consists of several pseudo-ternary and quasi-ternary composition triangles. Coexisting phases in the solid state at 260 °C were characterised by XRD analysis of the equilibrated samples. Quasi-ternary compounds were not found. The ternary eutectic temperature was observed at 315 ± 2 °C and its composition was delineated at 57 mol.% LiCl-42 mol.% KCl-1 mol.% GdCl₃ in the LiCl-KCl-K₃GdCl₆ composition triangle. The other ternary eutectic temperature was observed at 308 ± 2 °C in the LiCl-K₃GdCl₆-K₂GdCl₅ composition triangle. Its composition was deduced at 40.2 mol.% LiCl-41.7 mol.% KCl18.1 mol.% GdCl₃. Another ternary eutectic temperature was observed at 360 ± 9 °C in the LiCl-K₂GdCl₅-KGd₂Cl₇ composition triangle. Its composition was deduced at 33.8 mol.% LiCl-29.5 mol.% KCl-36.7 mol.% GdCl₃. The fourth ternary eutectic temperature was observed at 362 ± 4 °C in the LiCl-KGd₂Cl₇-LiGdCl₄ composition triangle. Its composition was delineated at 48 mol.% LiCl-11 mol.% KCl-41 mol.% GdCl₃. The ternary pseudo-peritectic reaction “L+GdCl₃ ↔ LiGdCl₄+KGd₂Cl₇” was observed at 370 ± 3 °C. Its composition was delineated at 46.7 mol.% LiCl-10.5 mol.% KCl-42.8 mol.% GdCl₃. The primary and secondary crystallisation temperatures, as well as polymorphic phase transformation temperatures of the samples were deduced from the heating runs of DTA experiments. Further, phases responsible for the various thermal events were ascertained. Isothermal composition triangles at selected temperatures, Scheil diagram and the polythermal liquidus projection with isothermal contours of the ternary phase field were drawn.

Phase equilibria in Ga-Sn-Te system plays a key role in designing multiphase thermoelectric materials. SnTe is a promising alternative to the well-known PbTe (toxic) thermoelectric phase in the Ga-Sn-Te system. In the present study, various compositions have been selected using the thermodynamically developed database of the Ga-Sn-Te system to understand the phase equilibria and microstructural features. The alloys with multiphase combinations of SnTe, Ga₆SnTe₁₀, GaTe, and Te were produced using vacuum induction melting. In addition, the developed microstructures were characterized using x-ray diffraction, optical and Scanning Electron Microscopy techniques. The microstructures reveal interesting eutectic morphologies of Ga₆SnTe₁₀/Te, Ga₆SnTe₁₀/SnTe, and GaTe/SnTe. The microstructural features were explained using Scheil-Gulliver cooling calculations. Moreover, the thermal analysis of the investigated alloys was also performed to validate the thermodynamically predicted liquidus temperatures and various phase transitions in the investigated alloys.

The equilibrium phase relations of the Nd₂O₃-CaO-Fe₂O₃ system were investigated at 1473 K in air using a high-temperature isothermal equilibration technique followed by quenching. Using x-ray diffraction (XRD) and scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS) analysis of quenched samples, twelve two-phase equilibria regions and eleven three-phase equilibria regions were observed. A series of solid solutions Nd_1−xCa_xFeO_3−δ formed in the ranges of 0 ≤ x ≤ 0.2, 0.5 ≤ x ≤ 0.6, and 0.6 < x ≤ 1 were found. Ternary compound Ca_1−xNd_1+xFeO_4−δ was observed to be stable at 1473 K with limited substitution of Nd by Ca. The 1473 K isothermal section was constructed for the Nd₂O₃-CaO-Fe₂O₃ system.