Phase equilibria and crystal structures of solid solutions in the Sr-Fe-Ni-O system at 1100°C in air

The phase equilibria in the Sr-Fe-Ni-O system at 1100°C in air have been studied by x-ray diffraction, and the corresponding phase diagram at constant temperature and pressure has been constructed. The system has been shown to contain two solid-solution series at 1100°C in air: SrFe_{1 ? x} Ni _x O_{3 ? δ} (0 < x ≤ 0.075, sp. gr. Cmmm) and Sr₃(Fe_{1 ? y} Ni _y )₂O_{7 ? δ} (0 < y ≤ 0.15, sp. gr. I4/mmm). Neither Sr₄(Fe_{1 ? z} Ni _z )₆O₁₃ nor Sr(Fe_{1 ? z} Ni _z )₁₂O₁₉ solid solutions have been identified. The lattice constants and structural parameters of single-phase samples have been refined by the full profile Rietveld analysis method.     

Phase equilibria and transformation in the Ti–Al–Ta system

Journal of Materials Science - TiAl- or Ti3Al-based alloys have gained industrial applications in recent years. The incorporation of β-stabilizing element Ta has demonstrated to better adjust...     

Interdiffusion inα solid solutions of the Cu-Zn-Sn system

The interdiffusion coefficients in the f c c phase of Cu-Zn-Sn alloys, , have been determined at 1073 K. The concentration profiles indicate that the diffusion rate of tin is greater than that of zinc in the Cu-Zn-Sn alloy. The diffusion paths show the typical S-shaped curves. All of the four interdiffusion coefficients are positive and they are very sensitive to the solute concentration. The atomic mobilities of the three diffusing elements in Kirkendall planes increase in the order of Cu, Zn, Sn. The interaction energy of the Cu-Sn bond is much larger than that of the Zn-Sn bond. From the results of the present work it seems that the Onsager reciprocal relation holds in the a phase of the Cu-Zn-Sn system.     

Phase equilibria in the system Sm–Rh–O and thermodynamic and thermal studies on SmRhO3

Using isothermal equilibration, phase relations are established in the system Sm–Rh–O at 1273 K. SmRhO₃ with GdFeO₃-type perovskite structure is found to be the only ternary phase. Solid-state electrochemical cells, containing calcia-stabilized zirconia as an electrolyte, are used to measure the thermodynamic properties of SmRhO₃ formed from their binary component oxides Rh₂O₃ (ortho) and Sm₂O₃ (C-type and B-type) in two different temperature ranges. Results suggest that C-type Sm₂O₃ with cubic structure transforms to B-type Sm₂O₃ with monoclinic structure at 1110 K. The standard Gibbs energy of transformation is $ \Delta_{\text{tr}} G^{\text{o}} ( \pm 87)/{\text{J}}\,{\text{mol}}^{ - 1} = 3763 - 3.39\,(T/{\text{K}}) $ . Standard Gibbs energy of formation of SmRhO₃ from binary component oxides Rh₂O₃ and Sm₂O₃ with B-type rare earth oxide structure can be expressed as $ \Delta_{\text{f(ox)}} G^{\text{o}} ( \pm 75)/{\text{J}}\,{\text{mol}}^{ - 1} = - 64230 + 6.97(T/{\text{K}}) $ . The decomposition temperature of SmRhO₃ estimated from the extrapolation of electrochemical data is 1665 (±2) K in air and 1773 (±3) K in pure oxygen. Temperature-composition diagrams at constant oxygen pressures are constructed for the system Sm–Rh–O. Employing the thermodynamic data for SmRhO₃ from emf measurement and auxiliary data for other phases from the literature, oxygen potential-composition phase diagram and 3-D chemical potential diagram for the system Sm–Rh–O at 1273 K are developed.     

Phase transitions in alloys of the Ni–Mo system

The structure of Ni–20 at.% Mo and Ni–25 at.% Mo alloys heat treated at different temperatures was studied by the method of transmission electron microscopy. X-ray photoelectron spectroscopy was used to detect the sign of the chemical interaction between Ni and Mo atoms at different temperatures. It is shown that at high temperatures the tendency toward phase separation takes place. The system of additional reflections at positions {1 ½ 0} on the electron diffraction patterns testifies that the precipitation of crystalline bcc Mo particles begins in the liquid solution. At 900 °C and below, the tendency toward ordering leads to the precipitation of the particles of the chemical compounds. A body-centered tetragonal phase Ni₄Mo (D1_a) is formed in the Ni–20 at.% Mo alloy. In the Ni–25 at.% Mo alloy, the formation of the Ni₃Mo (D0₂₂) chemical compound from the A1 solid solution has gone through the intervening stage of the Ni₄Mo (D1_a) and Ni₂Mo (Pt₂Mo) formation.     

Experimental investigation and thermodynamic calculation of the phase equilibria in the Cu–Mo–Ni ternary system

The phase equilibria at 900 °C, 1000 °C, 1100 °C, 1200 °C and 1300 °C in the Cu–Mo–Ni system were experimentally determined by means of optical microscopy (OM), electron probe microanalyzer (EPMA) and X-ray diffraction (XRD) on the equilibrated alloys. The experimental results firstly found that the fcc-type miscibility gap exists at 900 °C, 1000 °C, 1100 °C and 1200 °C in the Cu–Mo–Ni system, and the solubility of Cu in the MoNi phase at 900 °C, 1000 °C, 1100 °C and 1200 °C are about 0.5 at.%, 1.5 at.%, 1.7 at.% and 4.0 at.%, respectively. The as-cast Cu₂₀Mo₂₀Ni₆₀ (at.%), Cu₂₀Mo₃₀Ni₅₀ (at.%), Cu₁₀Mo₆₀Ni₃₀ (at.%), Cu₇₀Mo₁₀Ni₆₀ (at.%), Cu₂₀Mo₆₀Ni₂₀ (at.%) and Cu₈₀Mo₁₀Ni₁₀ (at.%) alloys appear the separated macroscopic morphologies, which are caused by the liquid phase separation on cooling, while the as-cast Cu₁₀Mo₂₅Ni₆₅ (at.%), Cu₃₂Mo₅Ni₆₃ (at.%) and Cu_30.7Mo_6.3Ni₆₃ (at.%) alloys show the homogenous microscopic morphologies. On the basis of the experimental data investigated by the present and previous works, the phase equilibria in the Cu–Mo–Ni system were thermodynamically assessed by using CALPHAD (Calculation of Phase Diagrams) method, and a consistent set of the thermodynamic parameters leading to reasonable agreement between the calculated results and experimental data was obtained.     

Experimental investigation and thermodynamic calculation of phase equilibria in the In–Sb–Zn ternary system

Binary thermodynamic data, successfully used for phase diagram calculations of binary systems In–Sb, In–Zn, and Sb–Zn, were used for prediction of phase equilibria in ternary In–Sb–Zn system. The liquidus projection, invariant equilibria and several vertical sections were calculated using the CALPHAD method. Alloys, situated along three calculated vertical sections, were investigated by differential thermal analysis (DTA). The experimentally determined phase transition temperatures were compared with predicted results. Phase identification of selected samples was done using scanning electron microscopy (SEM) with energy dispersive X-ray microanalysis (EDS).     

Phase transformations in the ternary Ag–Ga–Sb system

Phase diagram of the Ag–Ga–Sb ternary system was extrapolated using calculation of phase diagrams (CALPHAD) method. Phase transition temperatures of the alloys with compositions along three vertical sections with constant molar ratios Ga/Sb = 1, Ag/Ga = 1 and Ag/Sb = 1 were measured using differential scanning calorimetry (DSC). Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDX) was used for identification of phases in equilibrated samples. Experimental results were compared with thermodynamic prediction.     

Decomposition of supersaturated solid solutions in Al–Cu–Mg–Si alloys

The Al–Cu–Mg–Si alloying system is a base for a diverse group of commercial alloys which acquire their properties after quenching and aging. Therefore, the knowledge of the phase composition of hardening precipitates and the conditions under which they are formed is very important. ast reference data were analyzed along with experimental results and calculations of phase equilibria. Different alloys were compared based on the composition of the supersaturated solid solution. It is shown that the phase composition of aging products in alloys with Mg : Si > 1 agrees well with the equilibrium phase composition at a temperature of annealing. However, the sequence of precipitation in the alloys with Mg : Si < 1 is more complicated. The hardening in these alloys occurs with precipitation of the and phases and their precursors. The former phase may contain copper and later transforms either to and (Mg₂Si) or to Q phase depending on the amount of copper and annealing temperature.     

Phase equilibria in the system ZnO-B2O3-SiO2 at 950° C

Phase equilibria in the system ZnO-B₂O₃-SiO₂ investigated at 950°C using quenching and X-ray powder diffraction techniques. The binary phases reported reviously were confirmed but no ternary phases were found. Solid-solution effects were investigated for the primary and binary phases by comparison of patterns; no solid solutions were detected. There is a large Quid area in the high-B₂O₃ corner of the phase diagram. h is found that zinc orthosilicate,-2ZnO · SiO₂, dissolves in this to form a zinc-oxide-rich borosilicate liquid but 4ZnO · 3B₂O₃ does not. Them is also a liquid eutectic at approximate composition 65ZnO-25B₂O₃-10-SiO₂ (wt%). The rate of volatilization and loss of B₂O₃ was also investigated for 4ZnO · 3B₂O₃ and it was concluded that although volatilization occurs, the loss was insufficient at the firing times and temperature used to invalidate the major features of the diagram.     

Phase transformation in the Al2O3–ZrO2 system

Co-precipitation methods have been used to produce 20 mol% Al2O3–80 mol% ZrO2 mixed oxides, from aqueous solutions of zirconium oxychloride and aluminium chloride, followed by precipitation with ammonia. The resulting gel was calcined at increasing temperatures, and X-ray diffraction confirmed that the structure remained amorphous up to 750°C and then crystallized as a single-phase cubic zirconia solid solution, but with a reduced unit-cell dimension. At higher temperatures, the unit-cell dimension increased and, above 950°C, this phase started to transform to a tetragonal zirconia (t-ZrO2) phase, again of reduced cell dimensions compared with t-ZrO2, with simultaneous appearance of small amounts of -Al2O3. Above 1100°C, the tetragonal phase transformed to monoclinic zirconia on cooling, and the amount of -Al2O3 increased. Above 1200°C, the -Al2O3 transformed to the stable -Al2O3. These results confirm that aluminium acts as a stabilizing cation for zirconia up to temperatures of about 1100°C. © 1998 Chapman & Hall     

Liquid–liquid phase equilibria,density difference,and interfacial tension in the Al–Bi–Si monotectic system

We have performed thermodynamic calculation of the phase equilibria in the ternary monotectic system Al–Bi–Si. The liquid–liquid miscibility gap in the Al–Bi–Si system extends over almost the entire concentration triangle. The thermal analysis data for (Al_0.345Bi_0.655)_100−x Si _x alloys (x = 2.5, 5, 7.5, and 10 wt%) excellently agree with the calculated phase diagram. The experimental density difference of the coexisting liquid phases shows a good agreement with the density difference calculated in the approximation of ideal solution using the densities of pure elements and the compositions of L′ and L′′ from the thermodynamic calculation. The liquid–liquid interfacial tension in the (Al_0.345Bi_0.655)_100−x Si _x liquid alloys increases with Si content. The experimental temperature dependence of the interfacial tension is well described by the power low in reduced temperature (T _C–T) at approach of the critical temperature with the exponent μ = 1.3, which is close to the value predicted by the renormalization group theory of critical behavior.     

Fabrication and properties of novel composites in the system Al–Zr–C

Composite bodies in the system Al–Zr–C, with about 95% relative density, were obtained by heating the compact body of powder mixture consisting of Al and ZrC (5 : 1 mol %) in Ar at 1100–1500°C for various lengths of time. Components of the material heated at more than 1200°C were Al, Al3Zr, ZrC and AlZrC2. The Al3Zr exhibited plate-like aggregation, and its size increased with increasing temperature. In the material heated at 1500°C for 1 h, the largest plate-like Al3Zr aggregation was 2000 m long and 133 m thick. Then the AlZrC2 was present as well-proportioned hexagonal platelet particles with a 8–9 m diameter and a 1–2 m thickness in the interior of the plate-like Al3Zr aggregation and Al matrix phase. The average three-point bending strength of the bodies was 140–190 MPa, and the maximum strength was 203 MPa in the body heated at 1300°C for 1 h. The body heated at 1500°C for 1 h showed high oxidation resistivity to air up to 1000°C.     

Thermodynamic Properties of Melts and Phase Equilibria in the Copper–Zirconium System

The vapor composition over and thermodynamic properties of Cu–Zr melts (5.1–85.0 at. % Zr) are studied by Knudsen cell mass spectrometry between 1191 and 1823 K. The data set obtained comprises more than 1100 activity values for various compositions and temperatures. The thermodynamic behavior of Cu–Zr melts is described in terms of the associated-solution approach with an accuracy no worse than the experimental accuracy. The melts are shown to contain two molecular species: CuZr and Cu₂Zr. The contributions of different types of chemical bonding to the Gibbs energy and enthalpy of formation of Cu–Zr melts are asymmetrical and shifted from the equiatomic composition in opposite directions: the extremum of covalent bonding is shifted to the Cu-rich side, while metallic bonding is more significant in Zr-rich alloys. The rapid temperature variation of covalent bonding leads to a large excess heat capacity C _p ^E of the melts and a negative excess entropy _f S ^E, which rapidly drops with decreasing temperature. It is shown that not only C _p ^E and _f S ^E but also their temperature variations are governed by the parameters of association reactions and depend more strongly on the entropy than on the enthalpy of complex formation. This indicates that, in the general case, the glass-forming capabilities of melts are independent of the interparticle interaction and accounts for the pronounced tendency of Cu–Zr melts toward amorphization.     

Conduction mechanism and dielectric properties of BiFeO3–BaTiO3 solid solutions

The first measurements are reported for the frequency-dependent conductivity of (1?x)BiFeO₃–xBaTiO₃ (x = 0.10, 0.15 and 0.30) solid solutions in the frequency range of 10⁰–10⁶ Hz and in the temperature range of 50–300 °C. Powder X-ray diffraction confirms the formation of solid solutions. The dielectric properties were seen to improve with increasing BaTiO₃ (BT) content. The conductivity (AC and DC) measurements reveal an inverse variation of the frequency exponent ‘s’ with temperature, high density of states and thermally activated process. The calculated density of states was found to be N(E_f) = 80.2 × 10³² eV^?1 cm^?1 at 1 kHz and 50 °C for BiFeO₃–10 % BaTiO₃ (BFO–10 % BT) solid solution. The impedance spectroscopy analysis confirms the presence of grain and grain boundary affecting the conductivity. Our results provide the first unambiguous evidence of conduction in crystallite BFO–BT solid solutions through correlated-barrier-hopping model.