Study Of Phase Equilibria Research Articles

Phase equilibria of (water + [EMIM] bromide) and (water + [EMIM] tosylate)

This work presents a detailed phase equilibria study on the aqueous solutions of two hydrophilic ILs that are solid at room temperature: 1-ethyl-3-methylimidazolium bromide ([EMIM][Br]) and 1-ethyl-3-methylimidazolium tosylate ([EMIM][TOS]). The melting temperatures of the pure ILs were measured to discriminate between existing literature data that show some disparity. Solid-liquid equilibrium (SLE) data for (water + [EMIM][Br]), so far lacking in the literature, were determined by a dynamic method over the major portion of the entire composition range. Using a chilled mirror dew point technique, extensive and accurate vapor-liquid equilibrium (water activity) measurements were further conducted for the aqueous solutions of both ILs. The temperature and concentration dependences of the activity data were correlated simultaneously by an extended NRTL model, whereby establishing a common description of pertinent equilibria and related thermodynamic behavior of these systems. Good performance of this model was verified against other experimental data from the literature and this work. In particular, correct predictions of experimental SLE data proved the model to extrapolate well beyond the temperature range of data underlying the correlation. Excess thermodynamic properties calculated from the model revealed that these systems exhibit large negative deviations from Raoult's law, a strongly exothermic mixing and, except for (water + [EMIM][TOS]) in the water-rich region, positive excess entropies. Comparing the two ILs, the observed deviations from ideality are always more pronounced for [EMIM][Br], which indicates that [Br]– is a more hydrophilic anion than [TOS]–. The observed pattern of thermodynamic behavior was rationalized on the molecular level by means of simple MD simulations. They showed that while there are more H-bonds formed between water and [TOS]–, these bonds are weaker than those between water and [Br]–.

Crystallization of late-stage MORB under varying water activities and redox conditions: Implications for the formation of highly evolved lavas and oxide gabbro in the ocean crust

In order to understand late magmatic processes that occur in the deep oceanic crust, we performed a phase-equilibria study in a representative late-stage system at a pressure of 200 MPa with a special focus on the role of water and oxygen fugacity. The starting composition for the experiments was evaluated based on a statistical approach using evolved fresh MORB glasses from the database PETDB highest in FeO and TiO2 (in average 17.92 wt% and 3.73 wt%, respectively), assumed to represent frozen liquids erupted at the seafloor generated by extensive differentiation of MORB.We conducted crystallization experiments in a range of temperatures from 850 to 1050 °C with water activities from 0.1 to 1 and under redox conditions from FMQ-1.1 to FMQ + 3.2 (FMQ = fayalite-magnetite-quartz oxygen buffer). The results show that in this Fe- and Ti-rich late-stage system, Fe-Ti-oxides are the liquidus phases followed by clinopyroxene, apatite, and plagioclase, which is more stable at low water activity. Amphibole is stable at high aH2O and at temperatures lower than 900 °C. The evolution of the melt composition with decreasing temperature and aH2O follows in general the liquid lines of descent observed in other experiments in ferrobasaltic compositions. Orthopyroxene, which occurs as late crystallizing phase in many oceanic gabbros, was absent among the experimental mineral assemblages. Based on the evolution of coexisting clinopyroxene and plagioclase compositions, our experiments define a trend similar to the trends from other suites of oceanic gabbros from various locations.Our experimental results shed new light on the formation of highly evolved lavas from fast- and intermediate spreading mid-ocean ridges implying a relatively simple two-step differentiation model. First, primitive MORBs differentiate along the 1 atm cotectic trend to typical ferrobasaltic compositions by fractionation of olivine, plagioclase, clinopyroxene. This trend continues as long as Fe-Ti oxides are not saturated, which is strongly dependent on the prevailing oxygen fugacity. When such ferrobasaltic magmas are cut off from replenishment by fresh MORB, the possibility for further differentiation to highly evolved melts is given by fractionation of oxides, clinopyroxene, plagioclase, apatite and finally amphibole and apatite. Phase relations obtained in our experiments help to understand the formation of oxide gabbros from the ultra-slow spreading Southwest Indian Ridge (IODP drill core Hole 735B). The experimental evaluated crystallization order with temperature is in accord with the record of crystallization of the Hole 735B oxide gabbros.

Study of the physicochemical properties of protein kinase CK2 inhibitors -TBBt, TBBi and 2-Me-TBBi

The examination of physicochemical properties of selected protein kinase CK2 inhibitors: 4,5,6,7-tetrabromo-1H-benzotriazole (TBBt), 4,5,6,7-tetrabromo-1H-benzimidazole (TBBi) and 4,5,6,7-tetrabromo-2-methyl-1H-benzimidazole (2-Me-TBBi) was performed. The study includes modification of synthesis method and determination of compounds' thermal properties, the solid-liquid phase equilibria and pKa. Thermal properties (melting temperature, enthalpy of fusion, temperature and enthalpy of phase transitions) were determined by means of differential scanning calorimetry (DSC). For solid-liquid phase equilibria study, as a solvent, three liquids were used independently: water, ethanol and 1-octanol. In order to elicit the inhibitors’ solubility with alcohols (ethanol and 1-octanol), the dynamic method was applied. In the case of poorly soluble inhibitors in water, equilibria were determined by spectrophotometric method. Based on a phase diagram obtained results were interpreted and correlated using three equations: Wilson equation, NRTL equation and UNIQUAC equation.pKa values of studied polybrominated benzoazoles were estimated by the spectrophotometric Bates–Schwarzenbach method at two constant temperatures: 298.15 K as a room temperature and 310.15 K as a human body temperature.Obtained results are very important for further design of CK2 inhibitors, because they provide information about the solubility of pharmacophore in binary systems: active compound (1) + solvent (2), that may be used in differentiating the way how to apply potential drug. Moreover, all values of dissociation constants bring valuable guidelines to establish the therapeutic dose of pharmaceutics.

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

The phase equilibria in the ternary Tl–Se–I system have been investigated by means of differential thermal analysis, X-ray powder diffraction and the electromotive force measurements (EMF) of electrochemical cells relative to the thallium electrode with ionic liquid as an electrolyte. Several polythermal sections, the isothermal section at 300 K and the projection of the liquidus surface of the system have been constructed. The homogeneity and primary crystallization regions of intermediate phases, as well as types and coordinates of non- and monovariant equilibria have been determined. Formation of two congruently melting ternary compounds (Tl5Se2I at 720 K, and Tl6SeI4 at 705 K) was observed. It was revealed that the system is characterized by the existence of wide areas of α- (based on Tl2Se) and δ-solid solutions (based on Tl5Se2I). Standard thermodynamic functions of formation and standard entropies of Tl5Se2I and Tl6SeI4 compounds were calculated based on the thermodynamic study of Tl–Se–I alloys by the EMF measurements with an ionic liquid electrolyte.

The solid solution–aqueous solution system (Sr,Ba,Ra)SO4 + H2O: A combined experimental and theoretical study of phase equilibria at Sr-rich compositions

Solid solution formation between RaSO4 and other isostructural sulfates has been known for a long time as a process potentially controlling Ra concentrations in aquifers. Here, we measured the Ra uptake in the Sr-rich corner of the ternary (Sr,Ba,Ra)SO4 solid solution - aqueous solution (SS-AS) system by equilibrating SrSO4, BaSO4 and mixed (Sr,Ba)SO4 solids with Ra-bearing aqueous solutions for up to 1302 days at 90 °C at a solid/liquid ratio of 5 g/L. The recrystallization experiments were combined with electron microscopy studies of the solids. The evolution of the solid and aqueous phases was interpreted based on thermodynamic modelling applying a recently revised thermodynamic dataset for the (Sr,Ba,Ra)SO4 + H2O system.The recrystallization process involved several metastable phases, starting from the least soluble, Ba- and Ra-rich precipitates and ending with Sr-rich solids, whose compositions approached the predicted equilibrium states. The composition and the time evolution of metastable phases were correlated with changes in the computed supersaturation functions. Particularly, the formation of Ra- Ba- and Sr-rich rims on primary barite grains in the experiment with the mechanical mixture of 99% of celestine and 1% of barite has been explained by combining calculated supersaturation conditions with considerations of structural misfit.A key result was the observed final Raaq concentration which is about one order of magnitude lower compared to the initial concentration, implying an efficient uptake into the newly formed solid phases. These concentrations appeared to be just slightly lower than those predicted by the thermodynamic calculations, implying that the complete SS-AS equilibrium was close to be reached in Sr-rich systems in the recrystallization experiments lasting for about 3.5 years.

Multiple timescale constraints for high-flux magma chamber assembly prior to the Late Bronze Age eruption of Santorini (Greece)

The rhyodacitic magma discharged during the 30–80 km3 DRE (dense rock equivalent) Late Bronze Age (LBA; also called ‘Minoan’) eruption of Santorini caldera is known from previous studies to have had a complex history of polybaric ascent and storage prior to eruption. We refine the timescales of these processes by modelling Mg–Fe diffusion profiles in orthopyroxene and clinopyroxene crystals. The data are integrated with previously published information on the LBA eruption (phase equilibria studies, melt inclusion volatile barometry, Mg-in-plagioclase diffusion chronometry), as well as new plagioclase crystal size distributions and the established pre-LBA history of the volcano, to reconstruct the events that led up to the assembly and discharge of the LBA magma chamber. Orthopyroxene, clinopyroxene and plagioclase crystals in the rhyodacite have compositionally distinct rims, overgrowing relict, probably source-derived, more magnesian (or calcic) cores, and record one or more crystallization (plag ≫ opx > cpx) events during the few centuries to years prior to eruption. The crystallization event(s) can be explained by the rapid transfer of rhyodacitic melt from a dioritic/gabbroic region of the subcaldera pluton (mostly in the 8–12 km depth range), followed by injection, cooling and mixing in a large melt lens at 4–6 km depth (the pre-eruptive magma chamber). Since crystals from all eruptive phases yield similar timescales, the melt transfer event(s), the last of which took place less than 2 years before the eruption, must have involved most of the magma that subsequently erupted. The data are consistent with a model in which prolonged generation, storage and segregation of silicic melts were followed by gravitational instability in the subcaldera pluton, causing the rapid interconnection and amalgamation of melt-rich domains. The melts then drained to the top of the pluton, at fluxes of up to 0.1–1 km3 year− 1, where steep vertical gradients of density and rheology probably caused them to inject laterally, forming a short-lived holding chamber prior to eruption. This interpretation is consistent with growing evidence that some large silicic magma chambers are transient features on geological timescales. A similar process preceded at least one earlier caldera-forming eruption on Santorini, suggesting that it may be a general feature of this rift-hosted magmatic system.

Experimental and correlational study of phase equilibria in aqueous solutions of phosphoric acid with alcohols at different temperatures

Liquid-liquid equilibrium (LLE) data were measured for the aqueous mixtures of phosphoric acid with 1-pentanol and 1-heptanol at T=(298.2, 308.2, and 318.2) K and atmospheric pressure. These ternary systems exhibit as Treybal's type-1 liquid-liquid phase behavior. The reliability of the experimental tie-lines was checked using the Othmer-Tobias and Hand correlation equations. The activity coefficient models of NRTL and UNIQUAC were applied to fit the experimental tie lines. For these models, values of the binary interaction parameters between each pair of components in the studied systems were obtained. Experimental distribution coefficients and selectivity factors for the immiscibility regions were determined.

How deceptive are microstructures in granitic rocks? Answers from integrated physical theory, phase equilibrium, and direct observations

In this contribution, we address the vexed question of the extent to which microstructures in granitic rocks reflect their igneous histories or have been masked by later events. The previous works have tended to address the problem either using theoretical or modelling considerations, or by interpretation of observed microstructures. Here, we use an approach that integrates the theory of microstructural development and the results of experimental phase-equilibrium studies with direct observation of natural examples on a variety of scales. We show that the predictions of the theoretical and experimental approaches agree perfectly with the mesoscopic and microscopic evidence from granitic rocks themselves. Our conclusion is that although, in many cases, granitic rock microstructures have been modified by near-solidus reactions and crystallisation, in the absence of tectonic deformation the fundamental elements of their igneous heritage remain intact. This means that it is perfectly in order to infer aspects of crystallisation sequences, magmatic reactions, and magma flow through careful microstructural observations. Thus, our answer to the question of how deceptive granitic textures are is, in most instances, ‘not very’. However, some undeformed plutons have undergone fluid-driven alteration, and others have been affected by contact metamorphism. Thus, each case should be examined on its own merits.

Experimental and thermodynamic modeling study of the solid-liquid equilibrium in the ternary system (NaCl + NaClO 3 + H 2 O) at 293.15 and 333.15 K and 0.1 MPa

Abstract The study of the solid-liquid phase equilibrium for (NaCl + NaClO 3 + H 2 O) system is of significance to understand the thermodynamic property of the aqueous solution of ionic membrane electrolysis process to promote the production of sodium hydroxide (caustic soda). The solubilities and the physicochemical properties including density, refractive index and pH for this ternary system at 293.15 and 333.15 K and 0.1 MPa were measured using the isothermal dissolution method. Based on Pitzer ion-interaction model and its extended HW model, the solubility equilibrium constants K sp of NaClO 3 and the mixing ion-interaction parameters ( θ Cl,ClO3 , Ψ Na, Cl,ClO3 ) at 293.15 and 333.15 K were parameterized in this work. The Debye-Huckel limiting slope A o , the Pitzer single-salt parameters of NaCl and NaClO 3 and the solubility equilibrium constants K sp of NaCl at 293.15 and 333.15 K were taken from the relative temperature-dependence formula in the literature. A comparison shows that the calculated solubilities of the ternary system at 293.15 and 333.15 K agree well with the experimental data. The calculated results of densities and refractive indices using the empirical equations agree well with the experimental data at 293.15 and 333.15 K.

Thermochemistry of BaSm2O4 and thermodynamic assessment of the BaO–Sm2O3 system

AbstractThe BaO–Sm2O3 system is of interest for the optimization of synthesis of electroceramics. The only systematic experimental study of phase equilibria in the system was performed more than 40 years ago. The reported experimental values of the enthalpy of formation of BaSm2O4 are in conflict, and the reported compound Ba3Sm4O9 has never been confirmed. In this work we synthesized BaSm2O4 by solid‐state reaction and determined its heat capacity, enthalpy of formation, and phase transitions by differential scanning calorimetry, high‐temperature oxide melt solution calorimetry and ultra‐high‐temperature differential thermal analysis, respectively. We confirmed the existence of Ba3Sm4O9 and its apparent stability from 1873 to 2273 K by X‐ray diffraction on quenched laser‐melted samples but were not able to obtain single‐phase material for calorimetric measurements. The CALPHAD method was used to assess phase equilibria in the BaO–Sm2O3 system, using both available literature data and our new measurements. A self‐consistent thermodynamic database and the calculated phase diagram of the BaO–Sm2O3 system are provided. This work can be used to model and thus to understand the relationships among composition, temperature, and microstructure for multicomponent systems with BaO and Sm2O3.

Synthesis and Characterization of Diethyl Citrate and Phase Equilibria in Mixtures with Ethanol and Water

In this work, diethyl citrate (DEC) was synthesized and isolated for further physicochemical characterization and phase equilibria study. The synthesis was performed via partial esterification of citric acid with ethanol, and the final product was separated from the resulting mixture using a pH-controlled solvent extraction method. Characterization using 1H NMR and 13C NMR spectroscopy confirmed the presence of both DEC isomers with few impurities. Results indicate that a 6:5 molar ratio of the symmetric to the nonsymmetric ester structures was attained during synthesis. Thermogravimetric analysis and differential scanning calorimetry allowed us to measure, for the first time, glass transition temperature (228 K) and decomposition temperature (493 K) of diethyl citrate. Additionally, P–x data for the vapor–liquid equilibrium of the binary mixtures diethyl citrate + ethanol and diethyl citrate + water were collected at 308 K using an accurate dynamic device. Data were regressed to generate binary interacti...

Development of a thermodynamic model for the Li2CO3-NaCl-Na2SO4-H2O system and its application

Abstract The study of the solid-liquid phase equilibrium for the Li2CO3-NaCl-Na2SO4-H2O system is of significance to separate lithium from the mother liquor obtained by the reaction of lithium chloride/lithium sulfate and sodium carbonate. The phase equilibrium data for the binary system of Li2CO3-H2O, the ternary systems of Li2CO3-NaCl-H2O and Li2CO3-Na2SO4-H2O, and the quaternary system of Li2CO3-NaCl-Na2SO4-H2O over the temperature range from 283.15 K to 363.15 K were measured. Based on the Pitzer’s model embedded in the Aspen Plus™, the phase equilibrium data for the systems of NaCl-H2O, Na2SO4-H2O and NaCl-Na2SO4-H2O taken from literatures were firstly predicted to verify the applicability of parameters from the default database and literatures. Subsequently, besides the solubility of Li2CO3 in water at different temperatures, the values for the systems of Li2CO3-NaCl-H2O and Li2CO3-Na2SO4-H2O at 298.15 K and 343.15 K were correlated, and then the obtained parameters can well predict the phase equilibrium data for the systems of Li2CO3-NaCl-H2O, Li2CO3-Na2SO4-H2O Li2CO3-NaCl-Na2SO4-H2O at T = (313.15, 323.15 or 363.15) K. Through the rigorous thermodynamic model representing the Li2CO3-NaCl-Na2SO4-H2O system developed, the phase diagram of the ternary Li2CO3-NaCl-H2O system at T = (298.15, 343.15 or 363.15) K visualized with lucidity, and the course of crystallization to produce Li2CO3 from the mother liquor was illustrated. All of these will provide a thermodynamic basis for the separation of lithium from mother liquor and optimization of Li2CO3 production process.

Phase Equilibrium Study of the Ternary System CO2 + H2O + Ethanol At Elevated Pressure: Thermodynamic Model Selection. Application to Supercritical Extraction of Polar Compounds

The purpose of this study is to select an appropriate thermodynamic model among the ones available in commercial process simulators for representing the phase behavior of the carbon dioxide + ethanol + water system. The following versions of the Soave-Redlich-Kwong (SRK) and Peng-Robinson (PR) cubic equations of state (EoS) were considered: Panagiotopoulos-Reid, modified Panagiotopoulos-Reid, Huron-Vidal-NRTL, Modified Huron-Vidal (MHV2-UNIFAC), Predictive Soave-Redlich-Kwong (PSRK) and Volume-Translated Peng–Robinson (VTPR). The Polar Perturbed-Chain SAFT EoS deriving from the Statistical Associating Fluid Theory (PPC-SAFT) was also selected for the present investigation. This study highlighted that the optimal thermodynamic models for the application of interest have to be chosen among the VTPR, PSRK and MHV2-UNIFAC EoS. Once identified a suitable thermodynamic model for the CO2 + ethanol + water ternary system, it has been possible then to simulate the extraction process of polar compounds from natural products and to discuss how water influences the process efficiency.

Phase equilibria study on bromide-based ionic liquids with glycols and sulfolane. Experimental data and correlation

In this work new experimental data on (solid + liquid) phase equilibria of nine binary mixtures composed of bromide-based ILs, namely: 1-ethyl-1-methylmorpholinium bromide, [EMMOR][Br], 1-butyl-1-methylmorpholinium bromide, [BMMOR][Br] and 1-butyl-3-methylimidazolium bromide, [BMIM][Br] with diethylene glycol, triethylene glycol and sulfolane are presented. One of the tested IL, [BMIM][Br] has been synthesized and the structure was confirmed by NMR technique. The experimental SLE data for the tested binary systems have been determined using dynamic method. NRTL and Wilson equations were used to correlate the experimental data. Additionally, the basic characterization of pure ILs have been done; temperature and enthalpy of melting have been determined using DSC technique. The density and dynamic viscosity of pure organic solvents have been determined at wide temperature range. The influence of IL’s structure on mutual solubility with diethylene glycol, triethylene glycol and sulfolane is discussed.

Isobaric Vapor-Liquid Phase Diagrams for Multicomponent Systems with Nanoscale Radii of Curvature.

At any given temperature, pressure, and composition, a compound or a mixture of compounds will exist either in a single phase, whether solid, liquid, or vapor, or in a combination of these phases coexisting in equilibrium. For multiphase systems, it is known that the geometry of the interface impacts the equilibrium state; this effect has been well-studied in single component systems with spherical interfaces. However, multicomponent phase diagrams are usually calculated assuming a planar interface between phases. Recent experimental and theoretical work has started to investigate the effect of curved interfaces on multicomponent phase equilibrium, but these analyses have been limited to isothermal conditions or to a portion of the isobaric phase diagram. Herein, we consider complete vapor-liquid phase diagrams (both bubble and dew lines) under isobaric conditions. We use Gibbsian composite-system thermodynamics to derive the equations governing vapor-liquid equilibrium for systems with a spherical interface separating the phases. We validate our approach by comparing the predicted nitrogen/argon dew points with reported literature data. We then predict complete isobaric phase diagrams as a function of radius of curvature for an ideal methanol/ethanol system and for a nonideal ethanol/water system. We also determine how the azeotropic composition of ethanol/water changes. The effect of curvature on isobaric phase diagrams is similar to that seen on isothermal phase diagrams. This work extends the study of curved-interface multicomponent phase equilibrium to isobaric systems, expanding the conditions under which nanoscale systems, such as nanofluidic systems, shale gas reservoirs, and cloud condensation nuclei, can be understood.

Influence of Adsorption and Capillary Pressure on Phase Equilibria inside Shale Reservoirs

As a result of the small pore sizes and organic content of shale, capillary pressure and adsorption are two effects that should be taken into account in the study of phase equilibrium inside shale. The inclusion of both effects in the phase equilibrium modeling can shed light on how bulk phase composition inside the porous media changes with the temperature and pressure and how the phase equilibrium changes accordingly. In the long run, such a model can be used in reservoir simulation for more complicated analysis. In this study, we present a calculation method that can effectively include adsorption and capillarity. We propose to introduce an excess adsorbed phase and treat the remaining substance inside the pores as a bulk phase (gas, liquid, or both) to make the mass balance formulation simpler. The adsorbed phase is modeled by the multicomponent Langmuir (ML) equation for its simplicity and computational efficiency. A more theoretical adsorption model, the multicomponent potential theory of adsorption...

Solubility and thermodynamics of vitamin C in binary liquid mixtures involving water, methanol, ethanol and isopropanol at different temperatures

Abstract Vitamin C also known as ascorbic acid is an important compound for different fields of knowledge and applications. The development of separation processes and reaction media requires experimental information concerning solid-liquid equilibrium of the organic acid in different pure substances and mixtures. With the intention of raising solubility data, this research aims to perform a study of phase equilibrium involving vitamin C in mixtures formed by water/ethanol, water/isopropanol, methanol/ethanol, methanol/isopropanol and ethanol/isopropanol. The experiment was conducted throughout the molar composition range of the binary solution at the temperatures of 293.15 K, 303.15 K, 313.15 K and 323.15 K. The Jouyban-Acree model was applied in order to correlate the experimental solubility data and the adjustable parameters were calculated as a function of temperature. The experimental results were applied to thermodynamic relations to determine standard functions of dissolution. The increase of temperature leads to a larger amount of dissolved vitamin C. The solubility is also dependent on the solution concentration and that is interconnected with the dielectric constant of the binary solution. The Jouyban-Acree model is able to correlate the experimental data satisfactorily and the standard thermodynamic quantities of dissolution agree with the interpretation of the behavior experimentally observed.

Phase Equilibria in the Copper-Rich Corner of the Cu-Ce-La-O System at the Temperature Range 1100-1300 °C

The thermodynamic modeling and the experimental study of phase equilibria realized in the Cu-Ce-La-O system in the 1100-1300 °С temperature range were performed. The aim of the thermodynamic modeling was to estimate the possible deoxidization depth of a copper melt by cerium and lanthanum when they are simultaneously present in liquid copper, as well as the determination of the oxide phases that can result from such deoxidation. To simulate phase equilibria, a method to construct the solubility surface of the components in the metal melt was applied, in the calculation of which the equilibrium constants of the reactions occurring in the metallic melt of the system under study and the interaction parameters of the first order (according to Wagner) elements in liquid copper were used. As a result of modeling, the diagrams linking micro-changes in the composition of a metallic melt with qualitative changes in the composition of interaction products were constructed. Moreover, during the calculation, isotherms of oxygen solubility in a copper melt containing cerium and lanthanum were constructed. During the experimental part of the work, samples of the metal of the Cu-Ce-La-O system were melted and then examined with a scanning electron microscope equipped with an energy-dispersive spectrometer for electron microprobe analysis to determine the type of nonmetallic inclusions formed. The results of the work can be used to analyze the technological processes of the production of copper and its alloys.

Effect of HFC-134a as a Promoter of CO2 Hydrate: Phase Equilibrium, Dissociation Enthalpy and Kinetics

HFC-134a gas was investigated as a potential guest molecule to improve the thermodynamic conditions and formation rate for CO2 hydrate. In the phase equilibrium study, the equilibrium pressure of CO2 + HFC-134a was lower than that of pure CO2 gas, and the equilibrium pressure decreased gradually with increasing HFC-134a concentration. The dissociation enthalpy (ΔHd) was calculated using the Clausius–Clapeyron equation, and the ΔHd value also changed with increasing HFC-134a concentration. In particular, the ΔHd of 8 mol % HFC-134a-added CO2 hydrate was 143.2 kJ/mol, which was similar to that of pure HFC-134a (structure-II). In the kinetic study, the reactor was initially filled with CO2 + HFC-134a gas only and pure CO2 gas was then supplied as a source when the hydrate reaction proceeded. As a result, the formation rate of the HFC-134a mixture in the initial 2 min was faster than that of pure CO2. This was consistent with the gas chromatography results, which showed that HFC-134a occupies the cage at the ...

Phase diagrams in materials science of topological insulators based on metal chalcogenides

The literature data on topological insulators (TIs) based on metal chalcogenides, which constitute a new unique class of functional materials, are systematized here in the context of physicochemical analysis and crystal chemistry. An accent is on the phase diagrams of relevant systems and the crystal structures of the main TI types. We show that, for search and design of new phases having TI properties, it will be expedient to revise earlier constructed phase diagrams for some systems, especially BV–Se(Te) and AIV–BV–Te (AIV = Ge, Sn, Pb; BV = Sb, Bi) systems, using new approaches to studies of phase equilibria. There is also a need for systematic studies of complex systems involving binary and ternary TIs.