Thermodynamic Properties Of Intermetallic Compounds Research Articles

Thermodynamic Assessment of the Co-Zr System

The assessment of the Co-Zr system was carried out in the frameworks of the CALPHAD-method. Composition dependence of the excess Gibbs energy of liquid alloys and solid solutions in the system was described using Redlich–Kister polynomials. Compound Energy Formalism was used to describe the thermodynamic properties of intermetallic compounds. The current assessment takes into account a complete set of experimental data on the thermodynamic properties of the phases and phase equilibria. The phase diagram, coordinates of invariant equilibria, and thermodynamic properties of liquid and solid phases are calculated.

First-principle study of the structural, mechanical, electronic and thermodynamic properties of intermetallic compounds: Pd3M (M=Sc, Y)

The mechanical, electronic and thermodynamic properties of Pd3M (M[Formula: see text]=[Formula: see text]Sc, Y) compounds have been investigated using the Full Potential Linearized Augmented Plane Wave (FP-LAPW) formalism. The generalized gradient approximation (GGA) is used to treat the exchange–correlation terms. The calculated formation enthalpies and the cohesive energies reveal that the L12 structure is more stable than the D0[Formula: see text] one. The obtained lattice parameters and bulk modulus calculations conform well to the available experimental and theoretical results. The elastic and mechanical properties are analyzed and results show that both compounds are ductile in nature. The Debye temperature and melting temperature are also estimated and are in a good agreement with experimental findings. The total and partial densities of states are determined for L12 and D0[Formula: see text] structures. The density of states at the Fermi level, [Formula: see text]([Formula: see text]), indicates electronic stability for both compounds. The presence of the pseudo-gap near the Fermi level is suggestive of formation of directional covalent bonding. The number of bonding electrons per atom [Formula: see text] and the electronic specific heat coefficient [Formula: see text] are also determined. The quasi-harmonic Debye model has been used to explore the temperature and pressure effects on the thermodynamic properties for both compounds.

Electrochemical Synthesis and Thermodynamic Properties of Pr‐Ni Intermetallic Compounds in a LiCl‐KCl‐NiCl2‐PrCl3 Melt

AbstractIn this report, the electrochemical behaviors of Pr(III) and Ni(II) ions on a W electrode were investigated in LiCl‐KCl eutectic by cyclic voltammetry (CV), square wave voltammetry (SWV), chronopotentiometry (CP) and open‐circuit chronopotentiometry (OCP) techniques. From the results of electrochemical methods, different signals corresponding to seven kinds of intermetallic compounds in the phase diagram of Pr−Ni were observed. The thermodynamic properties of intermetallic compounds in the temperature range of 823–923 K were investigated by open‐circuit chronopotentiometry. With the evaluated apparent standard potentials of Pr−Ni intermetallic compounds, the Gibbs energies, enthalpies and entropies of formation were also calculated. The co‐reduction products by galvanostatic and potentiostatic electrolysis were characterized based on X‐ray diffraction (XRD) and scanning electron microscopy (SEM) coupled with energy dispersive X‐ray spectroscopy (EDS). The shape of the alloy obviously changes from granular to bulk, and the alloy phase changes from Pr‐rich to Ni‐rich. The co‐reduction products of PrNi5, PrNi2 and PrNi were identified.

Mechanical and thermodynamic properties of intermetallic compounds in the Ni–Ti system

The mechanical and thermodynamic properties of intermetallic compounds in the Ni–Ti system are studied by first-principles calculations. All phases show anisotropic elasticity in different crystallographic directions, in which Ni3Ti and NiTi2 are approaching the isotropy structure. The elastic moduli and Vicker’s hardness of Ni–Ti system intermetallic compounds decrease in the following order: Ni3Ti [Formula: see text] B2_NiTi [Formula: see text] B19[Formula: see text]_NiTi [Formula: see text] NiTi2, and Ni3Ti shows the best mechanical properties. The intrinsic ductile nature of Ni–Ti compounds is confirmed by the obtained [Formula: see text]/[Formula: see text] ratio. The temperature dependence of linear thermal expansion coefficients (LTECs) of the compounds is estimated by the quasi-harmonic approximation (QHA) method. Ni3Ti shows the largest values among all Ni–Ti intermetallic compounds. At room temperature, the LTEC for Ni3Ti is 8.92 × 10[Formula: see text] K[Formula: see text], which falls in between the LTEC of zirconia toughened alumina (ZTA) (7.0–9.5 × 106 K[Formula: see text]) and iron matrix (9.2–16.9 × 106 K[Formula: see text]); i.e., the thermal matching of the ZTA/iron composite will be improved by introducing Ni3Ti intermetallic compound into their interface. Other thermodynamic properties such as sound velocity and Debye temperature are also obtained.

Insights into structural and thermodynamic properties of the intermetallic compound in ternary Mg–Zn–Cu alloy under high pressure and high temperature

Under the projector-augmented wave approach, the structural and thermodynamic properties of various intermetallic compounds in Mg–Zn–Cu alloys are investigated. The calculated results indicate that the intermetallic compounds Cu0.7Zn2, CuZn, Mg4Zn8, Mg8Cu16 and Mg8Zn8Cu8 are elastically stable at zero temperature and pressure. Cu0.7Zn2, CuZn Mg4Zn8 and Mg8Cu16 are the ductility phases, and Mg8Zn8Cu8 is the brittleness phase. According to the calculations of the elastic constants and Young modulus, it is found that the plasticity of CuZn is the best while that of Mg8Zn8Cu8 is the worst. Based on the quasi-harmonic Debye model, the vibrational internal energy, vibrational Helmholtz free energy, vibrational entropy, heat capacity of constant volume, heat capacity at constant pressure, thermal expansion coefficient, Grüneisen parameter and Debye temperature of the intermetallic compounds in Mg–Zn–Cu alloy under high pressure and high temperature are also deeply discussed.

The thermodynamic properties of intermetallic compounds and solid solutions of Cu-Zr system

The thermodynamic properties of crystalline copper–zirconium alloys are investigated in a wide range of temperatures of 701–1740 K and compositions of 5.1–97.3 at. % Zr using the Knudsen method of mass-spectrometry, including the technique based on the initiation and study of equilibria involving volatile products. The equilibrium of zirconium with KF additives is studied to achieve minimal temperatures of measurements. The obtained data are used to produce, for the first time, a complete thermodynamic description of all intermetallic compounds, as well as solid solutions of copper in bcc-Zr, in the range from temperatures of crystallization of amorphous alloys to liquidus temperatures. The accuracy and reliability of the obtained thermodynamic functions are confirmed by the coincidence of the results of measurements in studying samples of different compositions under different experimental conditions (the material of the effusion cell, the size of the effusion orifice, the type of reaction additive), as well as by agreement of the results with one another and with independent experimental data on phase equilibria. The evidence of the existence of Cu2Zr and Cu5Zr8 phases is obtained, and the regularities of phase transformations in crystalline copper–zirconium alloys are revealed.

Thermodynamics of Homogeneous Crystal Nucleation in Al-RE Metallic Glasses

In the present paper, thermodynamic data of the Al-Ce and the Al-Nd systems are analysed by a new CALPHAD assessment, in which special emphasis is put on the description of the short range order in the undercooled liquid. A reliable description of the thermodynamics of the undercooled liquid and the amorphous phase can only be achieved by considering thermodynamic data of each metastable state. The results demonstrate a stabilization of the liquid phase on undercooling up to the glass transition temperature. The thermodynamic properties of intermetallic compounds are also reassessed. From the calculated Gibbs energies, the driving force for nucleation of primary fcc-Al and Al 11 RE 3 crystals from the Al-rich liquid and amorphous phase have been computed as a function of temperature.

Oxygen potential and the chemical state of the fission products ruthenium, rhodium and palladium in irradiated oxide fuels

Thermodynamic properties of intermetallic compounds of the type M 3U and M 3Pu where M = Ru, Rh or Pd, are reviewed. The critical oxygen potential of the oxide fuel matrix necessary for their formation is suggested.