Solubility in Ternary System NdCl3–PrCl3–H2O at 25°С

The solubility diagram of the quaternary system С60(ОН)24 – NdCl3 – PrCl3 – H2O and its ternary subsystems at 25°C was studied by the method of isothermal saturation in ampoules. In systems С60(ОН)24 – NdCl3 – PrCl3 – H2O and NdCl3 – PrCl3 – H2O isovalent substitution solid solutions crystallize with the miscibility gap (PrCl3)х(NdCl3)1-х•6H2O and (PrCl3)х(NdCl3)1-х•7H2O. In all systems there is one non-invariant point of the eutonic type corresponding to the saturation of the solution with two solid phases in the ternary subsystems and three solid phases in the quaternary system

Recent review articles on high entropy alloys (HEAs) provide little information about miscibility gaps in multicomponent systems, especially about how to respond with alloying should they be found. Also, there is a lack of information about how miscibility gaps might appear on calculated or measured multicomponent phase diagrams. In this work concepts concerning miscibility gaps that form in binary and ternary systems are reviewed. Then the work is extended to alloys with more components including HEAs. The previous work predicts that there are significant differences between binary systems and those with three or more components. For example, miscibility gaps do not form in binary systems that have a negative heat of mixing, but they do form in ternary systems. Also, ternary systems with a positive heat of mixing can have their stability temperature lowered by adding ternary components that add positive heats of mixing. The morphology and topology of multicomponent/multiphase miscibility gaps differ from typical phase diagrams, as well. For example, one type of miscibility gap is said to have the rose geometry, because of its floral design. Normally only 2-phase miscibility gaps can form in binary and ternary systems. However using the Graph Method it is suggested that 3-phase miscibility gaps might form in HEA systems, even while trying to avoid them. A conclusion of this investigation is that with additional computational and experimental work it may be possible to expand the boundaries of where HEAs can be found.

Abstract.This research focuses on the development of effective protective coatings for carbon-carbon composite materials (CCСM), which are important components in high-temperature processes in aerospace engineering. The application of CCСM is limited by their sensitivity to oxidation, erosion and burnout in gas streams. In light of these limitations, our work is aimed at creating protective coatings using the method of self-propagating high-temperature synthesis, which provide increased performance and extend the service life of composites. The main task of the research is to identify the optimal compositions of powders for chromium-doped protective coatings through the SHS process. Various methods of obtaining protective coatings were analyzed, including chemical-thermal methods and methods of saturation from the liquid phase, revealing the peculiarities of the interaction of coatings with the CCСM matrix and changes in their mechanical characteristics. In addition to the classical methods of obtaining coatings, the method of surface saturation from the solid phase in an active gas environment as part of the SHS process was investigated. This method provides high-quality coating surfaces, reduction of processing time and the possibility of reaching high temperatures, depending on the composition of the SHS mixture. An important element of the research is the analysis of modern publications and research in the field of protective coatings. Special attention is paid to the problems associated with chemical interaction with the matrix of CCСM and uneven formation of carbide phases along the cross-section of the material. Experimental studies include a factorial experiment to identify the compositions of powder mixtures that provide high wear resistance. Various independent variables, such as chromium, silicon, titanium and aluminum content, are considered for their effect on the physical and mechanical properties of the coatings. The study focuses on the optimization of the parameters of thermal autoinitiation of SHS mixtures under process conditions. The regression equation for evaluating the dependences of the wear resistance of coatings on auto-initiation parameters and the content of alloying elements is given. The analysis of the research results includes the construction of three-dimensional graphic dependencies to optimize the wear resistance of coatings in the Cr-Al-Ti and Cr-Al-Si systems. Chromoalumosilicization of the coating showed better wear resistance, exceeding the wear resistance of untreated samples by 2.6-3.2 times, which allows the use of this technology for parts of aerospace equipment. It is interesting that the porous surface of coatings obtained by the SHS method prevents the penetration of oxygen into the material, contributing to the formation of oxide protective membranes, such as SiO2, TiO2, Cr2O3, Al2O3.

A basic analysis is performed to establish the interrelations between the equilibria existing when one solid phase {ox} is transformed into another solid phase {C n red} while both are in close contact with a solution containing both redox forms in the dissolved state. The transformation of the above solid phases by electrochemical reactions can be understood when the intermediate formation of mixed phases between {ox} and {C n red} is taken into account. Such a description allows solid state electrochemical reactions to be modeled for the case of an infinite miscibility of oxidized and reduced solid compounds as well as for the case of systems with miscibility gaps. It is shown that miscibility gaps will lead to a splitting of both the anodic and cathodic voltammetric peaks and also to a distinct separation of the anodic and cathodic reactions on the potential scale in voltammetric experiments. This phenomenon can be called an immiscibility polarization.

Thermodynamic modeling is a versatile tool for predicting the chemical composition cement during the hydration of cement. The quality of the thermodynamic modeling depends directly on the quality and completeness of thermodynamic database used. One of the main limitations of modeling the hydration of cement is the lack of thermodynamic data for Fe containing hydrates. In addition, the formation of solid solutions between Fe- and Al-containing hydrates could stabilize mixed solids. However, it is unclear to what extent such solid solution formation occurs. Also experimentally it is very difficult to identify Fe-containing hydrates in hydrating cements by standard analytical techniques as the signals from Fe-containing phases significantly overlap with those from the corresponding Al-containing phases. Thus, in this study, potential Fe-containing hydrates like Fe-hemicarbonate (Fe-Hc), Fe-monocarbonate (Fe-Mc), Fe-monosulphate (Fe-Ms), Fe-Friedel's salt (Fe-Fr), Fe-stratlingite (Fe-St), Fe-katoite (C3FH6 ) and Fe-siliceous hydrogarnet (Fe-Si-Hg) were synthesised at 20, 50 and 80 °C. The solid phases were characterized by X-ray powder diffraction (XRD), Thermogravimetric analysis (TGA), scanning electron microscopy (SEM), vibrational spectroscopy (Raman and Infrared spectroscopy) and Extended X-ray absorption fine structure spectroscopy (EXAFS). The compositions of the liquid phases were analyzed using inductively-coupled plasma optical emission spectrometry and mass spectrometry (ICP-OES and MS). At ambient temperature Fe-Mc, Fe-Ms, Fe-Fr and Fe-Si-Hg were stable, while Fe-Hc, Fe-katoite and Fe-St were metastable. Fe-Mc, Fe-Ms, Fe-Fr and Fe-Si-Hg were stable also at 50 °C, but the Fe-AFm phases were unstable at 80 °C while Fe-Si-Hg were stable up to above 100 °C. The measured composition of the liquid phase was used to calculate the solubility products at 20 and 50 °C and to derive the data for standard conditions (25 °C, 1 atm). The solubility products of Fe-Fr was similar to the solubility product of Al-Fr, while the solubility products of Fe-Mc and Fe-Ms were about 3 log unit lower than that of Al-Mc and Al-Ms indicating that in Fe-Friedel's salt is probably not stable in cements. The very low solubility product of Fe-Si-Hg (5 to 7 log units lower than that of Al-Si-Hg) implies that Fe-Si-Hg could be a stable phase in hydrated cements. Also the mixed Al- and Fe-containing hydrates were synthesized to study the extent of solid solution formation. Both XRD and thermodynamic modelling of the liquid compositions indicated that Al- and Fe-monosulphate and Al- and Fe-Friedel's formed solid solutions with a miscibility gap, while Al- and Fe- monocarbonate existed as two separate hydrates due to their different crystal structure (Al-Mc: monoclinic, Fe-Mc: rhombohedral). The formation of solid solution between Al and Fe-siliceous hydrogarnet seemed probable. To understand to what extent the findings from the synthesised hydrates were relevant for real cements, the speciation of iron was determined in hydrating cement using EXAFS spectroscopy. Identification of Fe-containing hydrates and quantification of their contributions was achieved by combining principal component analysis with iterative target tests, and linear combination. The results show that several Fe species already contributed to the overall Fe K-edge spectra of cement pastes during the first day of hydration. While ferrite was the dominant Fe-containing phase in the unhydrated cement, Fe-hydroxide was detected shortly after starting the hydration process. With time the formation of stable Al/Fe-siliceous hydrogarnet was observed, while the amounts of Fe-hydroxide and ferrite clinker slowly decreased. The latter finding agrees with results from thermodynamic modeling of the hydration process, which predicts formation of stable Al/Fe-siliceous hydrogarnet in cement system. The determination of the solubility products of these hydrates will help to extend the thermodynamic data base of cement minerals and establish whether and to which extent Fe-containing hydrates are stable in fresh and in leached cementitious systems. The results from this study on the Fe speciation in cementitious systems are important for a better understanding of cement-water interactions with a view to the durability of cementitious materials.

In this paper, we report the calculated phase diagrams of V-Nb, V-Ta, and Nb-Ta alloys computed by combining the total energies of 40–50 configurations for each system (obtained using density functional theory) with the cluster expansion and Monte Carlo techniques. For V-Nb alloys, the phase diagram computed with conventional cluster expansion shows a miscibility gap with consolute temperature T_c=1250 K. Including the constituent strain to the cluster expansion Hamiltonian does not alter the consolute temperature significantly, although it appears to influence the solubility of V- and Nb-rich alloys. The phonon contribution to the free energy lowers T_c to 950 K (about 25%). Our calculations thus predicts an appreciable miscibility gap for V-Nb alloys. For bcc V-Ta alloy, this calculation predicts a miscibility gap with T_c=1100 K. For this alloy, both the constituent strain and phonon contributions are found to be significant. The constituent strain increases the miscibility gap while the phonon entropy counteracts the effect of the constituent strain. In V-Ta alloys, an ordering transition occurs at 1583 K from bcc solid solution phase to the V_(2)Ta Laves phase due to the dominant chemical interaction associated with the relatively large electronegativity difference. Since the current cluster expansion ignores the V_(2)Ta phase, the associated chemical interaction appears to manifest in making the solid solution phase remain stable down to 1100 K. For the size-matched Nb-Ta alloys, our calculation predicts complete miscibility in agreement with experiment.

Solubility and kinetic properties of deuterium in single crystal Pd

Phase-field modeling of the particle size and average concentration dependent miscibility gap in nanoparticles of LixMn2O4, LixFePO4, and NaxFePO4 during insertion

Solid–liquid phase equilibrium and physicochemical properties (pH, nD, ρ) for the ternary system KCl + KH2PO4 + H2O at (298.15 and 313.15) K were investigated by the method of isothermal solution saturation and Schreinemaker’s wet residue. On the basis of the experimental data, corresponding phase diagrams and diagrams of physicochemical properties vs composition were plotted. In the phase diagrams, there are one eutonic point, two uninvariant curves, and two crystallization regions corresponding to KCl, KH2PO4. The phase diagrams of the ternary system show similar tendencies at different temperatures. At each temperature, the crystallization region of KH2PO4 is larger than that of KCl, and the crystallization region of KH2PO4 becomes larger as the temperature increases. Physico-chemical properties of the solid–liquid phase equilibrium solution vary regularly with the composition of KH2PO4 concentration. The experimental data have been satisfactorily compared with literature data. The measured data and ph...

The alumina-chromia system shows complete mutual solubility and is represented by an isomorphous phase diagram. However, the alumina-chromia system exhibits an asymmetric miscibility gap under 1300°C. Using existing data from the literature, the alumina-chromia system was assessed using thermodynamic modeling by Kim and Sanders [1]. Regular and subregular solution models for the liquid and solid phases were used to define the phase boundaries for the miscibility gap in this system. Using this thermodynamic representation of the miscibility gap to select temperatures of interest, 75 mole percent Al2O3samples were synthesized via combustion of powders, followed by pressing into pellets and heat-treated for various times and temperatures. Both X-ray and TEM analysis showed evidence of spinodal decomposition after heat-treatment. X-ray analysis showed that decreasing the heat-treatment temperature increases the compositional difference between the phases present. The experimentally observed microstructures exhibit lamella-like structures that vary in spacing from 8nm to 3nm as the heat-treatment temperature varies from 400°C to 800°C.

High temperature liquid phase epitaxy of (100) oriented GaInAsSb near the miscibility gap boundary

Thermodynamic analysis of miscibility gap due to ordering in ternary systems

Thermodynamic description on the miscibility gap of the Mg-based solid solution in the Mg–Zn, Mg–Nd and Mg–Zn–Nd systems

Solubility in triple water-salt systems containing LaCl3, GdCl3, SmCl3 chlorides and water-soluble fullerenol C60(OH)24 at 25oC was studied by the method of isothermal saturation in ampoules. The analysis for the content of rare earth elements was carried out by atomic absorption spectroscopy, for the content of fullerenol – by electronic spectrophotometry. Solubility diagrams in all four ternary systems are simple eutonic, both consist of two branches corresponding to the crystallization of fullerenol crystallohydrate and rare earth elements chloride crystallohydrates, and contain one non-invariant point corresponding to saturation with both solid phases. On the long branches of crystallization of C60(OH)24, a pronounced salting effect is observed – the solubility of C60(OH)24•18H2O decreases by a factor of more than a hundred compared with the solubility of fullerenol in water. On very short branches of crystallization of LaCl3•7H2O, GdCl3•6H2O, SmCl3•6H2O, the effect of salting-in effect is clearly observed, the solubility of all four chlorides increases markedly. All diagrams cannot be accurately approximated by Sechenov monoparametric equation – SE – and are very accurately approximated by Sechenov trinomial modified three-parameter equation SEM-3. Comparison of calculations in similar triple systems containing water-soluble fullerenol C60(OH)24 and NaCl, CuCl2, UO2Cl2 shows the applicability of the classical SE model to systems with NaCl, SEM-3 model and the four-parameter SEM-4 model for a system with UO2Cl2

The technique of annealing samples at a temperature at which both liquid and solid phases occur, followed by quenching to freeze‐in the solid phase, has been used to investigate equilibrium conditions off the pseudobinary section. It has been found that large three‐phase liquid‐solid‐solid fields occur corresponding to the two‐phase solid‐solid field of the pseudobinary section. The tie‐lines of the various two‐phase liquid‐solid fields have been determined together with the boundaries of the three‐phase fields at various temperatures in the range 600°–730°C. The locus of the cusp in the liquidus sheet corresponding to the liquidus point of the three‐phase field has also been found. Finally, the two solid phases of the three‐phase fields give the ranges of immiscibility in the pseudobinary section , and hence the variation of the miscibility gap with temperature has been determined. This gap is found to be very asymmetric even at temperatures a little below the peritectic horizontal, the solubility limits at 700°C being . The results are compared with the predictions of the simple solution model which give reasonable agreement with the liquidus data but poor agreement with the miscibility gap values.