Eutectic Phase Diagram Research Articles

Phase diagrams, eutectic mass ratios and thermal energy storage properties of multiple fatty acid eutectics as novel solid-liquid phase change materials for storage and retrieval of thermal energy

A series of binary and multiple fatty acid eutectics such as ternary eutectics, quaternary eutectics and quinary eutectics were successfully prepared and developed as solid-liquid phase change materials (PCMs) by using five kinds of individual fatty acids such as capric acid (CA), lauric acid (LA), myristic acid (MA), palmitic acid (PA), and stearic acid (SA) through melt blending followed by ultrasonication method. The eutectic phase diagrams of binary/multiple fatty acid eutectics were plotted and analyzed on the basis of Schrader equation and MATLAB software, and then their eutectic mass ratios were precisely determined by eutectic phase diagrams and differential scanning calorimetry (DSC) analyses. The deviations between the theoretical calculated eutectic mass ratios and the experimental determined eutectic mass ratios of some fatty acid eutectics could be attributed to the experimental errors of data obtaining from the DSC analyses, impurities of fatty acids and cumulative errors of calculation. The results of DSC indicated that phase change temperatures and enthalpies of the synthesized fatty acid eutectics gradually decreased with the increase of the number of components in the mixtures. The melting peak temperatures of the prepared binary eutectics, ternary eutectics, quaternary eutectics and quinary eutectics were varied from about 22 to 56°C, from about 18 to 49°C, from about 19 to 32°C and about 17°C, respectively. Their minimum and maximum melting enthalpies were about 127.2kJ/kg and 204.7kJ/kg, respectively. The spectra obtained from Fourier transformation infrared spectroscope showed that the binary/multiple fatty acid eutectics exhibited the similar carboxyl group with the single fatty acids and had stable chemical properties. The developed fatty acid eutectic mixtures were suitable for low temperature thermal energy storage applications such as solar water heating systems, building energy storage systems, and thermal regulating textiles.

Composite nanofibrous sheets of fatty acids and polymers as thermo-regulating enclosures

In this work we report fabrication and study of Polyvinyl Alcohol (PVA)-Fatty acids composite nanofibrous mats with an aim to develop thermo-regulating enclosures. Fatty acids, an important class of phase change materials (PCM), can serve as energy storage/recovery materials due to their high latent heats. PCM-PVA composite nanomats are fabricated by incorporating the PCMs into electrospun polymeric mats by two methods: (i) in ‘drop-cast’ composite mats, the molten liquid binary mixtures of the PCMs are gently dropped on to the electrospun PVA nanomats and fill the voids by capillary-suction, and (ii) in ‘mixed-and-spun’ composite mats, the fatty acid mixture solution is mixed with the PVA spinning solution and electrospun. The nanofibrous-mats of PVA and a series of mixtures of lauric acid (LA) and stearic acid (SA) prepared using the above two methods are characterized using differential scanning calorimetry (DSC), X-Ray diffractometry, and scanning electron microscopy. Phase diagrams constructed using the transition temperatures from DSC are interpreted as phase diagrams of the LASA binary mixture inside a nanofibrous polymeric medium, as opposed to its bulk phase diagram. The LASA mixture in PVA nanomats exhibits a eutectic phase diagram similar to their phase behavior in bulk. However, the eutectic temperature (Te) is significantly altered in composite nanomats as compared to its bulk value of 39.5°C: Te=34°C in “drop cast” composite mats, and further drops to 30°C in the “mixed-and-spun” composite mats. Tensile tests show considerable softening in the composite mats. Application of regular solution model suggests that an enhanced attraction between LA and SA components, attributed here to nanoconfinement, may be responsible for this change. SEM images show partial wetting of the PVA nanofibers by the fatty acids in “drop cast” composite mats and uniform fibers in “mixed-and-spun” composite mats samples. Thermoregulation ability of these mats is confirmed by monitoring the temperature vs. time profile inside a vial filled with hot water and wrapped around by the composite nanomats.

Thermal, spectroscopic and dissolution studies of lovastatin solid dispersions with acetylsalicylic acid

Lovastatin (LOV) is widely used for the treatment of hypercholesterolemia. The poor water solubility of LOV leads to its poor gastrointestinal absorption and results in poor bioavailability. In this study, a preparation of solid dispersions with acetylsalicylic acid (ASA) was studied to improve the dissolution rate of LOV. Solid dispersions were prepared using various mass ratios of both components through the grinding method. Differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR) and X-ray powder diffraction (XRPD) were used to characterize prepared solid dispersions. Their dissolution behaviors were also compared. LOV and ASA formed a simple eutectic phase diagram as indicated by DSC. The results obtained from FTIR spectroscopy and XRPD showed no evidence of drug–drug interaction. The dissolution studies indicated that the in vitro dissolution rate of LOV released from solid dispersions containing 10, 20, 40 and 60 mass% LOV was improved compared with the drug alone.

The solidification behavior and phase equilibrium of o-Nitroaniline-β-Naphthol binary eutectic system

ABSTRACTPhase diagram studies of o-nitroaniline-β-naphthol system have been made by the thaw melt method. Simple eutectic type phase diagram was formed. Formation of eutectic mixture occurred at 0.7222 mole fractions of o-nitroaniline and melted at 326.85 K. The heat of fusion of components and eutectic mixtures were determined with the help of DSC technique and excess thermodynamic functions were calculated. Experiments were performed to study the undercooling, microstructure and linear velocities of crystallization. Flexural strength measurements were also made. Eutectic mixture showed higher flexural strength as compared to the components.

Infrared thermography method for fast estimation of phase diagrams

Phase change materials (PCM) are widely used today in thermal energy storage applications. Pure PCMs are rarely used because of non adapted melting points. Instead of them, mixtures are preferred. The search of suitable mixtures, preferably eutectics, is often a tedious and time consuming task which requires the determination of phase diagrams. In order to accelerate this screening step, a new method for estimating phase diagrams in record time (1–3h) has been established and validated. A sample composed by small droplets of mixtures with different compositions (as many as necessary to have a good coverage of the phase diagram) deposited on a flat substrate is first prepared and cooled down to ambient temperature so that all droplets crystallize. The plate is then heated at constant heating rate up to a sufficiently high temperature for melting all the small crystals. The heating process is imaged by using an infrared camera. An appropriate method based on singular values decomposition technique has been developed to analyze the recorded images and to determine the transition lines of the phase diagram. The method has been applied to determine several simple eutectic phase diagrams and the reached results have been validated by comparison with the phase diagrams obtained by Differential Scanning Calorimeter measurements and by thermodynamic modelling.

Phase equilibria in the Tl2Te–YbTe–Te system

Phase equilibria in the composition region Tl2Te–YbTe–Te of the Tl–Yb–Te system have been studied by differential thermal analysis, X-ray diffraction, and scanning electron microscopy. We have constructed vertical sections along the YbTe–Tl2Te (Tl5Te3, TlTe, and Tl2Te3) joins and the liquidus projection below 1400 K. The results demonstrate that the former two joins have simple eutectic phase diagrams, whereas the latter two are not pseudobinary, because of the incongruent melting of the corresponding thallium tellurides, but are stable below the solidus line. The system contains no ternary compounds of composition Tl9YbTe6 or TlYbTe2, even though analogs exist in some Tl–Ln–Te systems.

Exploring Mg-Zn-Ca-Based Bulk Metallic Glasses for Biomedical Applications Based on Thermodynamic Approach

Magnesium (Mg)-based metallic glasses are considered as possible candidates in orthopedic implant applications. This paper aims to theoretically predict the glass-forming ability (GFA) in Mg-Zn-Ca alloy using a newly proposed thermodynamic model (P HHS), and the consistency of this model is verified through experimental analysis. P HHS is based on thermodynamic parameters such as enthalpy of chemical mixing, elastic enthalpy, and configurational entropy, thus incorporating the pivotal effects, i.e., electron transfer effects, effect of atomic size mismatch, and effect of randomness, which aid to high GFA. In essence, P HHS can be visualized as the energy barrier that exists between the transformations of random atomic structure of glass to ordered crystalline structure. When the P HHS value is more negative, the energy barrier will be high, supporting easy glass formation. Various Mg-Zn-Ca metallic glass compositions displayed almost an expected and supporting trend, where the critical diameter of the metallic glass rod increased with a more negative P HHS value. Among the predicted Mg-Zn-Ca systems, the Mg60Zn35Ca5 composition shows deviation from the expected trend. This discrepancy has been clearly elucidated using a eutectic phase diagram. In addition to the consistency of the P HHS parameter to verifying the GFA of various compositions, the unique ability of this model is to predict unexplored Mg-Zn-Ca glass-forming compositions using contour development. Thus, proving P HHS parameter to be used as an efficient tool in predicting new glass-forming compositions.

Measurements of the liquidus surface and solidus transitions of the NaCl–UCl3 and NaCl–UCl3–CeCl3 phase diagrams

NaCl–UCl3–PuCl3 is proposed as the fuel salt for a number of molten salt reactor concepts. No experimental data exists for the ternary system, and limited data is available for the binary compositions of this salt system. Differential scanning calorimetry is used in this study to examine the liquidus surface and solidus transition of a surrogate fuel-salt (NaCl–UCl3–CeCl3) and to reinvestigate the NaCl–UCl3 eutectic phase diagram. The results of this study show good agreement with previously reported data for the pure salt compounds used (NaCl, UCl3, and CeCl3) as well as for the eutectic points for the NaCl–UCl3 and NaCl–CeCl3 binary systems. The NaCl–UCl3 liquidus surface produced in this study predicts a 30–40 °C increase on the NaCl-rich side of the binary phase diagram. The increase in liquidus temperature could prove significant to molten salt reactor modeling.

Study of phase equilibria and the physicochemical properties of selected pharmaceuticals

In this work the phase equlibria in binary system: (Drug+solvent) was examined and their physicochemical properties were analyzed. The investigated substances were: synephrine (SYN), isoprenaline hydrochloride (IPR) and metaraminol bitartrate (MET). Solubility of this drugs was determined in three solvents: water, ethanol and 1-octanol. The molecular structure of these drugs is based on a phenthylamine skeleton, therefore all studied pharmaceuticals have an aromatic structure with different amounts of hydroxyl groups located at an aromatic ring. They also have different substituents on the amino group inside the chemical chain. The amino-group confers basic properties of the molecule, whereas the phenolic OH group is weakly acidic. The tested substances belong to the group of adrenergic drugs (adrenomimetics) and stimulate the sympathetic nervous system.Solubilities of three drugs were measured in the temperature range from 270K to 450K at constant pH. All of studied systems were described as simple eutectic phase diagrams, with complete miscibility at liquid phase and non-miscibility in solid phase. The results are presenting as two phases in equilibrium as a function of temperature. These studies are necessity when the drugs are introducing into the pharmaceutical field. The obtained experimental data were correlated with three equations: Wilson, NRTL and UNIQUAC. Moreover dissociation constants and corresponding pKa values of drugs were obtained with Bates–Schwarzenbach method at temperature 298.15K in the buffer solutions.The DSC (differential scanning microcalorimetry) was used to measure thermal basic properties of pure drugs, that is: the glass-transition temperature, temperature of melting, enthalpy of fusion and the heat capacity at the glass-transition temperature.

Phase equilibrium, crystallization behavior and thermodynamic studies of (m-dinitrobenzene + vanillin) eutectic system

The phase diagram of (m-dinitrobenzene+vanillin) system has been studied by the thaw melt method and an eutectic type phase diagram was obtained. The linear velocities of crystallization of the parent components and the eutectic mixture were determined. The enthalpy of fusion of the components and the eutectic mixture were determined using the differential scanning calorimetric technique. Excess Gibbs energy, excess entropy, excess enthalpy of mixing, and interfacial energy have been calculated. FTIR spectroscopic studies and flexural strength measurements were also made. The results have shown that the eutectic is a non-ideal mixture of the two components. On the basis of Jackson’s roughness parameter, it is predicted that the eutectic has faceted morphology.

Thermoelectric properties of a eutectic SnSe2-Bi2Se3 alloy

Data are presented which confirm that the SnSe2-Bi2Se3 system has a eutectic phase diagram, with a eutectic at 67 mol % SnSe2, melting at 831 ± 5 K. The thermoelectric properties of the eutectic alloy in this system have been studied for the first time in the temperature range 300–600 K. The results demonstrate that this alloy is a promising low-temperature thermoelectric material: its minimal thermal conductivity (χmin) and maximum thermoelectric figure of merit (ZTmax) are 0.28 W/(m K) (416 K) and 0.56 (593 K), respectively.

Solid–Liquid Equilibria for Six Binary Mixtures of Nonanedioic Acids, Decanedioic Acid, 3-Methylheptanedioic Acid, 2,2-Dimethylbutanedioic Acid, and 2,3-Dimethylbutanedioic Acid

Solid–liquid equilibria of dicarboxylic acids for binary mixtures—nonanedioic acid (1) + 3-methylheptanedioic acid (2) (eutectic temperature TE = 342.25 K, eutectic composition x1E = 0.364); nonanedioic acid (1) + 2,2-dimethylbutanedioic acid (2) (TE = 367.51 K, x1E = 0.653); nonanedioic acid (1) + 2,3-dimethylbutanedioic acid (2) (TE = 354.27 K, x1E = 0.463); decanedioic acid (1) + 3-methylheptanedioic acid (2) (TE = 352.47 K, x1E = 0.134); decanedioic acid (1) + 2,2-dimethylbutanedioic acid (2) (TE = 384.38 K, x1E = 0.483); and decanedioic acid (1) + 2,3-dimethylbutanedioic acid (2) (TE = 365.38 K, x1E = 0.192)—are measured using differential scanning calorimetry (DSC) and correlated using the Clarke–Glew equation in this study. Simple eutectic phase diagrams for these systems are observed. The experimental results are correlated using the Wilson and nonrandom two-liquid (NRTL) activity coefficient models, and satisfactory results are presented.

Mapping coexistence lines via free-energy extrapolation: Application to order-disorder phase transitions of hard-core mixtures

In this work, a variant of the Gibbs-Duhem integration (GDI) method is proposed to trace phase coexistence lines that combines some of the advantages of the original GDI methods such as robustness in handling large system sizes, with the ability of histogram-based methods (but without using histograms) to estimate free-energies and hence avoid the need of on-the-fly corrector schemes. This is done by fitting to an appropriate polynomial function not the coexistence curve itself (as in GDI schemes) but the underlying free-energy function of each phase. The availability of a free-energy model allows the post-processing of the simulated data to obtain improved estimates of the coexistence line. The proposed method is used to elucidate the phase behavior for two non-trivial hard-core mixtures: a binary blend of spheres and cubes and a system of size-polydisperse cubes. The relative size of the spheres and cubes in the first mixture is chosen such that the resulting eutectic pressure-composition phase diagram is nearly symmetric in that the maximum solubility of cubes in the sphere-rich solid (∼20%) is comparable to the maximum solubility of spheres in the cube-rich solid. In the polydisperse cube system, the solid-liquid coexistence line is mapped out for an imposed Gaussian activity distribution, which produces near-Gaussian particle-size distributions in each phase. A terminal polydispersity of 11.3% is found, beyond which the cubic solid phase would not be stable, and near which significant size fractionation between the solid and isotropic phases is predicted.

Impact of undercooling on epitaxially oriented liquid crystalline organizations of poly(3-hexylthiophene) below the eutectic temperature

For widely studied hole-transporting conjugated poly(3-hexylthiophene) (P3HT), the routes of liquid crystalline (LC) organization below the eutectic point were studied as a consequence of dissolution in molten hexamethylbenzene (HMB). Based on the variation of melting points with mixing compositions, the eutectic condition and phase diagram of these two crystallizable components were disclosed. Upon significant undercooling, the face-on LC organization of conjugated polythiophene epitaxially developed on formerly established HMB crystals. This face-on organization is featured with alternate layer stacking of organized thiophene stems with loosely aggregated regions by a nanometer scale of stacking periodicity. Differently, with a few degrees of undercooling below the eutectic point, edge-on organization preferably prevailed, which results in the anisotropic platelets extending along the chain direction. Regarding these prompt epitaxial LC organizations of conjugated polythiophene, the association of bead-like or worm-like fringe micelles in the molten state emerges as being elucidative for both structural and morphological features. After the sublimation of HMB crystals, the original face-on LC organization transformed to the crystalline packing of edge-on backbones via annealing above 160 °C. This evolution of molecular packing provides a new direction for deciphering the crystallization mechanism of conjugated polymers and the thread-like morphology.

Ionic Conductivity in Relation to Ternary Phase Diagram of Poly(ethylene oxide), Succinonitrile, and Lithium Bis(trifluoromethane)sulfonimide Blends

In an effort to develop free-standing lithium battery membrane, binary and ternary phase diagrams of poly(ethylene oxide) (PEO), bis(trifluoromethane)sulfonimide (LiTFSI), and succinonitrile (SCN) (i.e., solid plasticizer) mixtures have been established by means of differential scanning calorimetry and polarized optical microscopy. The occurrence of hydrogen bonds and/or coordination bonds in each binary pair (PEO/SCN, SCN/LiTFSI, and PEO/LiTFSI) was examined using Fourier transform infrared spectroscopy. The binary PEO/LiTFSI mixture exhibits a eutectic phase diagram with the liquid + crystal coexistence region having various crystal forms of the lithium salt, whereas the SCN/LiTFSI blend shows a wide noncrystalline region, which is highly desirable for organic solvent-free battery applications. The PEO/SCN blend shows a typical eutectic behavior, which is explicable in the framework of the Flory–Huggins theory in conjunction with the phase field theory of crystal solidification. Various coexistence regi...

Interaction of W2B5 with MeIV,VC carbides

It is established that the W2B5-MeIV,VC join in the W-B-C-MeIV,V quaternary systems is quasibinary, while polythermal joins are described by eutectic phase diagrams. It is shown that the eutectic composition and temperature correlate with the melting points of carbides and the Me d C content varies from 50 mol % in the W2B5-VC system to 4–6 mol % in the W2B5-TaC system. The existence of Me d C-Me d B2-W2B5 ternary eutectic systems promising for the development of new ceramics is proved.

Dendrite growth in annealed polymer blends for use in bulk heterojunction solar cells

This paper presents the evidence of growth of dendrites during the annealing of poly (3-hexylthiophene) and [6,6]-phenyl C61-butyric acid methyl ester (P3HT:PCBM) blends that are being explored for potential applications in bulk heterojunction polymer solar cells. These dendrites were observed in high resolution scanning electron microscopy to have morphologies that depend on the annealing temperature. Consistent with a recent eutectic phase diagram, the dendrites were not observed at 200 °C. The observations were explained by considering the effects of temperature on the kinetics of phase nucleation and growth in P3HT: PCBM blends. The implications of the results are also discussed for the stability of electrical properties in bulk heterojunction solar cells.

Metastable phase diagrams of Cu-based alloy systems with a miscibility gap in undercooled state

Some Cu-based alloy systems with a large positive enthalpy of mixing display a eutectic or peritectic phase diagram under equilibrium conditions, but show a metastable liquid miscibility gap in the undercooled state. When the melt is undercooled below certain temperature beyond the critical liquid-phase separation temperature, it separates into two liquids with different compositions. The compositions of the two liquids change successively upon the metastable phase diagram before solidification occurs. The shape and position of the metastable miscibility gap are dependent of the alloy components and their interaction features. This study reviews the metastable phase diagrams of Cu-based alloy systems, which are derived from experiments and thermodynamic calculations.

Engineering cocrystal thermodynamic stability and eutectic points by micellar solubilization and ionization

Pharmaceutical cocrystals are of great interest because of their potential to enhance solubility and bioavailability of poorly water-soluble drugs. Cocrystal development is however limited by their poor thermodynamic stability in aqueous environments. The work presented here describes the mechanisms by which cocrystal stability can be fine-tuned via micellar solubilization and ionization of cocrystal components. An important feature of cocrystal solution equilibria is the existence of eutectic points involving coexistence of three phases, a liquid and two solids. The solution composition at the eutectic points is a critical parameter that defines the conditions of thermodynamic stability. Equations that describe the sensitivity of eutectic points and phase diagrams to micellar surfactants and pH are presented. Predictions are in excellent agreement with the behavior of several carbamazepine cocrystals in aqueous solutions of sodium lauryl sulfate. Increasing the magnitude of micellar solubilization for one of the cocrystal components is found to confer greater thermodynamic stability to the cocrystal and expand its stability region. These findings provide an unprecedented level of control over cocrystal-solution phase behavior, and are applicable to multiple additives and solubilization mechanisms that may be required for the stabilization of highly soluble cocrystals.

Ternary phase diagrams of DNTF and TNAZ and their eutectics

The eutectic ternary phase diagrams of some typical volatilizable energetic materials have been investigated by high pressure differential scanning calorimeter (PDSC). The ternary H–X phase diagrams for TNT/TNAZ/DNTF (TTD) and TNAZ/DNTF/RDX (TDR) systems were constructed by the correlation of the apparent fusion heat with the composition (H–X method). And, the ternary T–X phase diagrams (the temperature dependence on composition) for the two ternary systems were constructed by calculating from the data of the five T–X binary phase diagrams. The eutectic compositions (mol%) of TTD and TDR ternary systems were obtained to be 52.3/27.3/20.4 (H–X method), 53.2/25.8/21.0 (T–X method) and 54.9/39.6/5.5 (H–X method), 55.1/42.2/2.7 (T–X method), respectively. The eutectic temperatures of the ternary systems were obtained by PDSC determination and T–X method calculation to be 76.5 and 76.7 °C, 47.5 and 50.2 °C, respectively. It is shown that the results obtained by two methods are in agreement and the error in measuring or calculating eutectic compositions and temperatures for the two ternary systems are within allowable ranges of ±3 mol% and ±3 °C, respectively. Moreover, by means of constructing two ternary H–X phase diagrams with different fixed composition of a component and comparing the apparent fusion heat of eutectics with calculated one, the results obtained from H–X method for TTD system were proved. The results showed that the gasification or volatilization of easy volatile materials could be efficiently restrained by high pressure atmosphere, and the perfectly and ideally H–X ternary phase diagrams can be constructed. In comparison with T–X method, H–X method has as a virtue of being quick and simple, especially on constructing ternary phase diagram.