Thermodynamic characteristics and phase equilibria in the alloys of the Ge–La system

Mixing enthalpies of melts of the Ge–La system have been measured using isoperibolic calorimetry within two concentration ranges. For the first range (0 < x _La < 0.16 at 1520 K and 0.16 < x _La < 0.29 at 1570 K), agreement with the known literature data is observed within the experimental error. The second range (0.78 < x _La < 1 at 1470 K and 0.7 < x _La < 0.78 at 1580 K) has been studied for the first time. The melts are characterized by very strong exothermal effects of mixing, which have almost symmetrical concentration dependence: ΔH? _La ^∞ = ΔH? _Ge ^∞ = ?245 kJ/mol at 1470 K. A thermodynamic optimization of the activities of the components and the phase diagram of the system have been conducted based on the obtained experimental data, using an ideal associated solution (IAS) model.     

Phase equilibria in the aluminium-rich side of the Al–Zr system

The Al-rich phase equilibria in the Al–Zr binary system were investigated experimentally. The phase diagram for compositions up to 40 at.% Zr was determined experimentally by differential thermal analysis and metallography. Three stable intermetallic compounds exist in this region of the diagram: Al₃Zr₂, Al₂Zr, and Al₃Zr. The peritectic melting of Al₃Zr₂ and the congruent melting of Al₂Zr were confirmed. Al₃Zr, the most Al-rich intermetallic compound, melts peritectically, which contradicts information available in the literature. In addition, the reaction between Al₃Zr and the (Al) solid solution seems to be of eutectic nature, in contradiction with previous results found in the literature. Based on these new experimental evidence, a revised phase diagram is drawn.     

Melt–gas phase equilibria and state diagrams of the selenium–tellurium system

The partial pressures of saturated vapor of the components in the Se–Te system are determined and presented in the form of temperature–concentration dependences from which the boundaries of the melt–gas phase transition are calculated at atmospheric pressure and vacuums of 2000 and 100 Pa. The existence of azeotropic mixtures is revealed. It is found that the points of inseparably boiling melts correspond to 7.5 at % of Se and 995°C at 101325 Pa, 10.9 at % at 673°C and 19.5 at % at 522°C in vacuums of 2000 and 100 Pa, respectively. A complete state diagram is constructed, including the fields of gas-liquid equilibria at atmospheric and low pressures, the boundaries of which allow us to assess the behavior of selenium and tellurium upon distillation fractionation.     

Phase equilibria in the Sn–As–Ge and Sn–As–P systems

T–x diagrams of polythermal GeAs–SnAs, GeAs–Sn₄As₃ sections of the Sn–As–Ge system and Sn₄P₃–Sn₄As₃ section of the Sn–As–P system were constructed using the results of X-ray powder diffraction and differential thermal analyses. It was found that the section GeAs–Sn₄As₃ is not quasi-binary due to realization of four-phase peritectic transformation L + SnAs ? GeAs + Sn₄As₃ at the temperature of 834 K. The quasi-binary section GeAs–SnAs represents a phase diagram of the eutectic type with the following coordinates of eutectic reaction: temperature of the eutectic point is 840 K, and composition is 20 mol% GeAs. In the Sn–As–P system, the existence of the solid-solution range indicated as (Sn₄As₃) _x (Sn₄P₃)_1?x  was defined. The polythermal section Sn₄P₃–Sn₄As₃ is not quasi-binary due to the fact that in the composition range with a high content of tin arsenide discussed section intersects the peritectic part of the three-phase volume (L + SnAs + α) of the ternary diagram.     

Experimental study of phase equilibria and thermodynamic properties of the Tl–Se–I system

Journal of Thermal Analysis and Calorimetry - The phase equilibria in the ternary Tl–Se–I system have been investigated by means of differential thermal analysis, X-ray powder...     

Study and 3D modeling of the phase diagram of the Ag–Ge–Se system

In view of the contradictoriness of the literature data, phase equilibria in the Ag–Ge–Se system were restudied by differential thermal analysis and X-ray powder diffraction analysis. A number of polythermal sections and an isothermal section at room temperature of the phase diagram were constructed, and so was the projection of the liquidus surface. The primary crystallization fields of phases and the types and coordinates of in- and monovariant equilibria were determined. It was shown that, in the system, a single ternary compound, Ag₈GeSe₆, forms, which undergoes congruent melting at 1175 K and a polymorphic transformation at 321 K. The formation of the compounds Ag₂GeSe₃ and Ag₈GeSe₅, which was previously reported in the literature, was not confirmed. Based on the phase diagrams of boundary binary systems and the results of the differential thermal analysis of a number of samples of the ternary system, equations were obtained for calculation and 3D modeling of the liquidus and phase-separation surfaces.     

Phase equilibria in the ternary system NaF–KF–CsF

The ternary eutectic system CsF–KF–NaF was studied by differential thermal analysis. The melting point and composition of the ternary eutectic were determined, and so was the boundary of the region of limited series of solid solutions within the composition triangle. The compositions of crystallizing phases were confirmed by X-ray powder diffraction analysis. The specific enthalpy of melting of the ternary eutectic was experimentally found.     

Solid state phase equilibria in the PtGaAs system

The PtGaAs solid state equilibrium phase diagram was determined at 600 °C with the use of X-ray powder diffraction, electron probe microanalysis (EPMA) and scanning electron microscopy (SEM). No ternary PtGaAs phases were found and limited solid solubility was measured in the constituent binary PtGa and PtAs compounds. GaAs, PtGa and PtAs₂ form a region of three-phase equilibrium which dominates the GaAs side of the phase diagram. The phase diagram is in agreement with previous observations that PtGa and PtAs₂ are the stable phases when platinum thin films are reacted to completion on GaAs.     

Phase equilibria and critical phenomena in the cesium nitrate–water–pyridine ternary system

The solubilities of components, phase equilibria, and critical phenomena in the cesium nitrate–water–pyridine ternary system are studied in the 5–100°C temperature range by the visual–polythermal method. Cesium nitrate is found to exhibit a salting-out effect at temperatures above 79.9°C causing phase separation in homogeneous water–pyridine solutions. The temperature of formation of the critical monotectic tie line (79.9°C) and the compositions of solutions corresponding to the liquid–liquid critical points at three temperatures are determined. The pyridine distribution coefficients between the aqueous and organic phases of the monotectic state at 85.0, 90.0, and 100.0°C are calculated. Their values demonstrate that salting-out of pyridine from aqueous solutions by cesium nitrate increases at higher temperatures. The plotted isotherms of phase diagrams confirm the fragment of the scheme of topological transformation of the phase diagrams of salt–binary solvent ternary systems with salting-in and salting-out phenomena.     

Reinvestigation of the paracetamol–caffeine,aspirin–caffeine,and paracetamol–aspirin phase equilibria diagrams

Many drug candidates are poorly soluble. The formation of solid dispersion can improve their solubility, consequently their bioavailability. For this purpose, the use of eutectic mixtures is well known in the pharmaceutical field. At the eutectic composition, both components are in reduced particle size and well dispersed. In this work, we focus on the combination of paracetamol, aspirin, and caffeine, which is highly effective for the treatment of migraine headache pain. We have reinvestigated the paracetamol–caffeine, aspirin–caffeine, and paracetamol–aspirin phase equilibria diagrams taking into account the polymorphism of caffeine, paracetamol, and aspirin. The three phase diagrams are determined using X-ray diffraction and the differential scanning calorimetry from the binary mixtures. It is concluded that the paracetamol–caffeine and aspirin–caffeine systems are similar and exhibit two invariants, one eutectic and one metatectic. The paracetamol–aspirin phase diagram reveals the formation of one eutectic. The composition of the three eutectics formed is confirmed by the related Tamman’s triangles. No compound formation is found in the three systems.     

Energetics, structures, bonding, and kinetics of the HSCl–HClS system

The [H,S,Cl] potential-energy surface has been investigated at the self-consistent field (SCF), complete active space self-consistent field (CASSCF), second-order M?ller–Plesset, coupled-cluster single-double and perturbative triple excitation, [CCSD(T)]/6-31G(d,p), 6-31G(2df,2pd), and correlation-consistent polarized valence triple zeta (cc-pVTZ) levels of theory. CCSD(T)/ cc-pVTZ results predict a very stable HSCl species, an isomer HClS, 51.84 kcal/mol higher in energy, and a transition state 57.68 kcal/mol above HSCl. Independent of the level of theory, results with the smaller 6-31G(d,p) basis set turned out to be poor, especially for HClS. Vibrational analysis indicates that both species can be easily differentiated if isolated. Bonding differences between these molecules are illustrated by contour plots of valence orbitals. Viewed classically, bonding in HClS involves a dative bond. Transition-state rate constants, and equilibrium constants for the HSCl ↔ HClS isomerization have been estimated for various temperatures (200–1000 K). At 298.15 K, the forward rate is predicted to be 7.95 × 10⁻²⁹ s⁻¹, and the equilibrium constant to be 2.31 × 10⁻³⁸. Tunneling corrections vary from 1.57 at 298.15 K to 1.05 at 1000 K. Activation energies have been obtained by a two-points linear fit to the Arrhenius equation. Received: 7 May 1999 / Accepted: 22 July 1999 / Published online: 4 October 1999     

Measurement and calculation of phase equilibria in the system n-pentane + poly(dimethylsiloxane) at 308.15–423.15 K

Vapor–liquid phase equilibria in the binary system n-pentane+poly(dimethylsiloxane) (PDMS) have been investigated experimentally at temperatures ranging from 308.15 to 423.15 K. The experiments have been performed at pentane mass fractions in the liquid phase ranging from 0 to 80% using the static method. PDMS with average molecular weights of 26 500 g/mol and 103 000 g/mol has been used. The data are in good agreement with several literature data by other researchers, mostly obtained by the use of inverse gas chromatography. The experimental data could be correlated well using the Flory–Huggins activity coefficient model for the polymer phase and the Peng–Robinson equation of state for the gas phase. Using statistical associating fluid theory (SAFT), it was only possible to reproduce the experimentally determined equilibria after adjusting the pure-component parameters of the polymer to the binary equilibria.Further, experimental data have been obtained for the R22 (difluorochloromethane)+PDMS system at 298.15 and 343.15 K.     

Phase equilibria involving solid solutions in the Li–Mn–O system

Phase equilibria involving LiMn₂O_4-, Li₂MnO_3-, LiMnO_2-, Mn₃O_4-, and MnO-base solid solutions were studied with varied temperature and partial oxygen pressure. The \({P_{{o_2}}}\)–T and x–y projections of the P–T–x–y phase diagram of the Li–Mn?O system were constructed, as well as the key x–y isotherms of the Li₂O–MnO–MnO₂ quasi-ternary system. In some experiments, the authors’ hydride lithiation method was employed to prepare lithium-rich homogeneous three-component nonstoichiometric phases.     

Phase equilibria in a polyethylene–polystyrene system

The method of optical interferometry is used to study the interaction of PE with PS in situ. On the basis of the obtained data, phase diagrams of the PE–PS system are constructed for a number of molecular masses of the components. For PE and PS oligomers, the UCMT values are determined. Pair parameters for the interaction of homopolymers are calculated, and their dependences on temperature and molecular mass are considered. The quantitative analysis of the behavior of high-molecular-mass fractions of PE and PS at high temperatures is carried out, and the regions of a partial compatibility of the components are predicted.