Calorimetric investigations of the MBr−NdBr3 melts (M=Li,Na, K,Cs)

Present work is a part of thermodynamic research program on the MX?LnX₃ system (M=alkali metal,X=Cl, Br andLn=lanthanide). Molar enthalpies of mixing in the LiBr?NdBr₃, NaBr?NdBr₃ and KBr?NdBr₃ liquid binary systems have been determined at temperature 1063 K by direct calorimetry in the whole range of composition. Investigated systems are generally characterized by negative enthalpies of mixing with minimum atX _NdBr3≈0.3–0.4. These enthalpies decrease with decrease of ionic radii of alkali metals. Molar enthalpies of solid-solid and solid-liquid phase transitions of K₃NdBr₆ and Cs₃NdBr₆ have been also determined by differential scanning calorimetry (DSC). K₃NdBr₆ is formed at 689 K from KBr and K₂NdBr₅ with enthalpy of 44.0 kJ·mol^?1 whereas Cs₃NdBr₆ is stable at ambient temperature and undergoes phase transition in the solid state at 731 K with enthalpy of 8.8 kJ·mol^?1. Enthalpies of melting have been also determined.     

Phase diagram and electrical conductivity of TbBr3-NaBr binary system

Several experimental techniques were used to characterise the physicochemical properties of the TbBr₃-NaBr system. The phase diagram determined by DSC, exhibits an eutectic and a Na₃TbBr₆ stoichiometric compound that decomposes peritectically (759 K) shortly after a solid-solid phase transition (745 K). The eutectic composition, x(TbBr₃)=39.5 mol%, was obtained from the Tamman method. This mixture melts at 699 K. With the corresponding enthalpy of about 16.1 kJ mol^-1. Diffuse reflectance spectra of the pure components and their solid mixtures (after homogenisation in the liquid state) confirmed the existence of new phase exhibiting its own spectral characteristics, which may be possibly related to the formation of Na₃TbBr₆ in this system. Additionally, the electrical conductivity of TbBr₃-NaBr liquid mixtures was measured down to temperatures below solidification over the whole composition range. This revised version was published online in July 2006 with corrections to the Cover Date.     

Determination and measurement of solid–liquid equilibrium for binary fatty acid mixtures based on NRTL and UNIQUAC activity models

The estimation of solid–liquid phase equilibrium is important for the design, development, and operation of many industrial processes because of application in many manufacturing fields such as cosmetic, pharmaceutic, and biotechnology industries. In this work, we measured solid–liquid phase equilibrium of six fatty acid binary mixtures using the DSC technique and developed thermodynamic approaches for binary fatty acid mixtures to estimate melting temperatures as a function of mole fraction in solid–liquid phase equilibrium. Derivation of NRTL and UNIQUAC activity models was developed to predict melting temperatures and latent heat to achieve eutectic points of undecylic acid, pentadecylic acid, margaric acid, and stearic acid six pairwise binary mixtures. The fatty acids eutectic mixtures are appropriate for heat water systems, phase clothes, concrete, and other similar applications. The results showed low deviations from experimental data measured in this study.

     

Thermodynamique des melanges binaires LiPO3-Pb(PO3)2: Diagramme de phases et étude thermodynamique du liquide

Study of solid-liquid phase diagram of LiPO₃-Pb(PO₃)₂ binary system, in certain calcination conditions, shows the existence of several metastable phasis. When heated at a temperature of 723 K the binary mixtures lead uncompletely to a defined compound Pb₂Li(PO₃). On heating these ternary solid mixtures, three eutectic reactions have been observed: LiPO₃+Pb(PO₃)₂→Liquid at a temperature of 793 K(1) LiPO₃+Pb₂Li(PO₃)₅→Liquid at a temperature of 843 K (2) Pb₂Li(PO₃)₅+Pb(PO₃)₂→Liquid at a temperature of 891 K (3) The metastable liquid phase appears in the system at temperature of 793 K. DTA experiments performed on the binary LiPO₃-Pb(PO₃)₂ mixtures, show a superposition of two diagrams. The first one is metastable and the second represents the stable equilibrium phase diagram. Measurements of liquid enthalpy of binary LiPO₃-Pb(PO₃)₂ system at temperature of 979.65 K were reported. The corresponding values were very small and so the binary system can be considered as athermal. Assuming an ideal behaviour, the liquidus curves in the metastable diagram were calculated and the eutectic reaction (LiPO₃-Pb(PO₃)₂→Liquid) was confirmed at 793 K. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermodynamic Study of the Molten Salt Binary System KHSO4−NaHSO4

The partial molar enthalpies of mixing of NaHSO₄ and KHSO₄ have been measured at 528 K by dropping samples of pure compounds into molten mixtures of NaHSO₄ and KHSO₄ in Calvet calorimeter. From these values the molar enthalpy of mixing has been deduced. The same method has been used for the determination of the heat capacity of the two pure compounds in the solid and liquid states. The phase diagram of this system has been confirmed by conductometric and thermal analysis methods. By an optimization method the excess entropy of the liquid mixtures was also calculated. This revised version was published online in August 2006 with corrections to the Cover Date.     

The phase diagram of CsNO<Subscript>3</Subscript>–RbNO<Subscript>3</Subscript>

The phase transitions of RbNO₃ and the binary phase diagram of (Cs,Rb)NO₃ were investigated at atmospheric pressure, using simultaneous direct and differential thermal analysis, μDTA and DSC techniques. A fourth phase transition of RbNO₃ has been observed at temperature near the melting point. The phase diagram of this system is characterised by a eutectic, two eutectoid and an azeotropic-like invariants. Three limited solid solutions and two continuous solid solutions have been detected at low temperature.     

Phase Diagram for the RbBr–CuBr System

The phase diagram for the RbBr–CuBr system has been determined. In the system two intermediate compounds are formed: RbCu₂Br₃, melting congruently at 537 K and Rb₃CuBr₄, melting incongruently at 544 K. The coordinates of the two eutectic points are: 501 K, 54 mole% CuBr and 522 K, 74 mole% CuBr. This revised version was published online in July 2006 with corrections to the Cover Date.     

Binary Mixtures of Liquid Crystalline Ester Bismaleimides

Abstract

A binary system consisting of a chlorohydroquinone-based ester bismaleimide (3-Cl), T _m = 238°C, and a methylhydroquinone-based ester bismaleimide (3-Me), T _m = 251°C, was investigated for the purpose of improving processability by widening the nematic phase range before polymerization. Calculations based on the Schroeder-van Laar equation predicted a system eutectic composition of 41% 3-Me monomer and a eutectic temperature of 202°C. Experiments found the eutectic composition at 35% 3-Me and the eutectic temperature at 218.5°C. Discrepancies between experimental results and theoretical predictions are likely due to error in measured heats of fusion either due to impurities in the samples or due to the reactive nature of the components being considered. Thermal cycling was also found to have a significant melting point depression effect. While significant depression of the system melting point was achieved, polymerization still occurred immediately after melting in all systems evaluated. All mixtures could be polymerized from the nematic phase to yield a solid which retained the nematic orientation of the starting polymer melt.     

Thermodynamic performance of the NaNO3–NaCl–NaNO2 ternary system

Calculations of phase diagram for additive ternary molten salt system are carried out by the conformal ionic solution theory. The liquidus temperatures of the system NaNO₃–NaCl–NaNO₂ are determined according to different types of solid–liquid equilibrium and different values of the binary interaction coefficients. For the system NaNO₃–NaCl–NaNO₂, the calculated and experimental temperatures differ are very small below 673 K, but the oxidation and decomposition of the mixed salts are found when the temperature is higher than 673 K. Meanwhile, the eutectic point is obtained from calculated phase diagram and the eutectic temperature is 507 K. Thermal stability of this eutectic mixture is investigated by thermo-gravimetric analysis device. Experimental results show this kind of molten salt has a lower melting point (501.28 K), similar to solar salt (493 K). It is thermally stable at temperatures up to 819 K, and may be used up to 827 K for short periods.     

Thermal investigation of PEG 4000 — oxazepam binary system

A thermal study using DSC and Hot Stage Microscopy (HSM) was carried out to investigate the interaction in solid state of the binary system PEG 4000 — oxazepam, and to establish their phase diagram. The eutectic composition, which melting occurs at lower temperature as compared with the pure components, has been determined. The results obtained by DSC and HSM have indicated that PEG 4000 — oxazepam mixtures displays no obvious incompatibilities, and that the system shows a typical eutectic behaviour. However because of the closeness of the melting of PEG 4000 to the eutectic temperature, it was difficult to determine precisely the eutectic composition and temperature on the basis of DSC measurements alone. The use of heats of fusion corresponding to physical mixtures allowed an estimation of the eutectic composition at 6% w/w oxazepam. Additional information of temperature (57.6C) and composition (5–10% w/w oxazepam) of the eutectic was obtained by HSM using the contact method. This low melting temperature in this range of compositions offers advantages in terms of drug stability and easy manufacture.     

Phase Diagram of the NaNO<Subscript>2</Subscript>—KNO<Subscript>3</Subscript> System in the 0 to 1 Molar Fraction Range of Concentrations of KNO<Subscript>3</Subscript>

The temperature dependence of the phase composition of KNO₃—NaNO₂ mixtures in the 0 to 1 molar fraction range of concentrations of KNO₃ is investigated. A phase diagram of the KNO₃—NaNO₂ binary system in the range of concentrations from 0 to 1 molar fractions of KNO₃ is drawn on the basis of DTA results. The composition of the eutectic mixture and its melting temperature is determined experimentally.     

Stable tetrahedron LiF–KI–K<Subscript>2</Subscript>CrO<Subscript>4</Subscript>–Li<Subscript>2</Subscript>CrO<Subscript>4</Subscript> of the quaternary reciprocal system Li,K||F,I, CrO<Subscript>4</Subscript>

The stable tetrahedron LiF–KI–K₂CrO₄–Li₂CrO₄ of the quaternary reciprocal system Li, K||F, I, CrO₄ was experimentally studied by differential thermal analysis. The compositions and melting points of mixtures of components at two eutectic points were determined. Based on experimental data, a T–x–y–z model of the phase complex was constructed, which allows one to solve problems of building polythermal and isothermal sections. A method for constructing the diagram of material balance of equilibrium phases for a given composition was developed. The diagram enables one to find the ratio between the amounts of the liquid and solid phases at constant temperature and also monitor the change in the composition of the phases within a chosen temperature range.     

Phase diagram of the system PbTe-As2Te3

TheT — x phase diagram of the pseudobinary system PbTe-As₂Te₃ was constructed from DTA data and results of X-ray diffraction analysis and electron-probe microanalysis. No new compound was found in the system PbTe-As₂Te₃. The phase diagram of this system is of an eutectic type with an eutectic temperature of 350±5°, the eutectic composition corresponding to 10 mole% PbTe. Two solid phases with compositions near to As₂Te₃ and PbTe, respectively, coexist in the system below the eutectic temperature. The solubility of PbTe in As₂Te₃ is smaller than 2 mole% PbTe, and that of As₂Te₃ in PbTe is smaller than 0.5 mole% As₂Te₃ at 290°.     

(Solid + liquid) phase equilibria and heat capacity of (diphenyl ether + biphenyl) mixtures used as thermal energy storage materials

The (solid + liquid) phase equilibrium for eight {x diphenyl ether + (1 − x) biphenyl} binary mixtures, including the eutectic mixture were studied by using a differential scanning calorimetry (DSC) technique. A good agreement was found between previous literature and experimental values here presented for the melting point and enthalpy of fusion of pure compounds. The well-known equations for Wilson and the non-random two-liquid (NRTL) were used to correlate experimental solid liquid phase equilibrium data. Moreover, the predictive mixture model UNIFAC has been employed to describe the phase diagram. With the aim to check this equipment to measure heat capacities in the quasi-isothermal Temperature-Modulated Differential Scanning Calorimetry method (TMDSC), four fluids of well-known heat capacity such as toluene, n-decane, cyclohexane and water were also studied in the liquid phase at temperatures ranging from (273.15 to 373.15) K. A good agreement with literature values was found for those fluids of pure diphenyl ether and biphenyl. Additionally, the specific isobaric heat capacities of diphenyl ether and biphenyl binary mixtures in the liquid phase up to T = 373.15 K were measured.     

Détermination expérimentale du diagramme de phase du système chlorure de cadmium-chlorure de potassium

A solid liquid phase equilibria diagram of Cd Cl₂K Cl has been obtained by thermal analysis. X-ray diffraction confirms deposition of pure components and of two compounds (Cd Cl₂ · K Cl) and (Cd Cl₂ · 4 K Cl). The first is congruently melting; the second is incongruently melting. Two eutectic and one peritectic transforms are observed for the mole fractions of K Cl 0.344, 0.620, 0.685 at the temperatures 658.5 K, 663.4 K, 733 K.     

Congruent melting of binary compounds with non-negligible vapour pressure

The sulfaguanidine—water (SG-H₂O) system is a binary system with non-negligible vapour pressure which presents a monohydrate. The phase diagram of this system is drawn from DTA experimental results, using the temperature-specific volume-molar fraction (T-v-x) model which was described in part I of this work. The melting of the monohydrate (SG, H₂O) is found to be congruent. Isochoric sections are drawn; they make it possible to determine the limits of the two eutectic invariant planes. The composition and specific volume of the vapour phase at the eutectic equilibrium of theSG-SG, H₂O subsystem are given. The triple line solid-liquid-vapour of the one-component phase diagram of the monohydrate is drawn. The experimental results are consistent with the congruent melting of the monohydrate. These results also show that the solid, liquid and vapour phase at the triple line have not the same composition.     

Thermodynamic and transport properties of the DyBr3–NaBr binary system

Phase equilibria in the DyBr₃–NaBr binary system were established from differential scanning calorimetry. This system exhibits incongruently melting compound Na₃DyBr₆ and one eutectic located at DyBr₃ molar fraction x = 0.409 (T = 711 K). Na₃DyBr₆ undergoes a solid–solid phase transition at 740 K and melts incongruently at 762 K. The specific conductivity of DyBr₃–NaBr liquid mixtures was measured over the whole composition range. Results obtained are discussed in term of possible complex formation.     

MnS-Ln2S3 (Ln = La, Nd, or Gd) phase diagrams; thermodynamics of phase transitions

The MnS-La₂S₃ phase diagram has been constructed where the incongruently melting compound Mn₂La₆S₁₁ is formed. Complex sulfide Mn₂La₆S₁₁ is characterized by monoclinic structure; its incongruent melting temperature is 1535 K. Eutectic coordinates are 31 mol % La₂S₃, 1490 K. The extent of the ??-La₂S₃ based solid solutions at 1570 K is 8 mol % MnS; at 770 K, ??-La₂S₃ dissolves 3 mol % MnS. The MnS-Gd₂S₃ system is a eutectic with limited solid solutions. Eutectic coordinates are 35.5 mol % Gd₂S₃, 1640 K. Solubility in ??-Gd₂S₃ is 28 mol % MnS at 1570 K, in ??-Gd₂S₃ is 13 mol % MnS at 1170 K, and in MnS is 1 mol % Gd₂S₃. Thermochemical equations have been composed for eutectic and eutectoid phase transformations. A MnS-Nd₂S₃ phase diagram has been predicted.     

Thermal conductivities of solid and liquid phases for pure Al,pure Sn and their binary alloys

The variations of thermal conductivities of solid phases versus temperature for pure Sn, pure Al and Sn–0.5 wt.% Al, Sn–2.2 wt.% Al, Sn–25 wt.% Al, Sn–50 wt.% Al, Sn–75 wt.% Al binary alloys were measured with a radial heat flow apparatus. From thermal conductivity variations versus temperature, the thermal conductivities of the solid phases at their melting temperature and temperature coefficients for same materials were also found to be 60.60 ± 0.06, 208.80 ± 0.22, 69.70 ± 0.07, 80.30 ± 0.08, 112.30 ± 0.12, 142.00 ± 0.15, 188.50 ± 0.20 W/K m and 0.00098, 0.00062, 0.00127, 0.00114, 0.00112, 0.00150, 0.00116 K⁻¹, respectively. The thermal conductivity ratios of liquid phase to solid phase for the pure Sn, pure Al and eutectic Sn–0.5 wt.% Al alloy at their melting temperature are found to be 1.11, 1.13, 1.06 with a Bridgman type directional solidification apparatus, respectively. Thus the thermal conductivities of liquid phases for pure Sn, pure Al and eutectic Sn–0.5 wt.% Al binary alloy at their melting temperature were evaluated to be 67.26, 235.94 and 73.88 W/K m, respectively by using the values of solid phase thermal conductivities and the thermal conductivity ratios of liquid phase to solid phase.     

Diagrammes de phases des systemes binaires KNO3-CsNO3 et KNO3-NaNO3

(K?Na)NO₃ and (K?Cs)NO₃ phase diagrams were drawn using a simultaneous thermal analysis technique in the range 373 to 623 K. The first phase diagram shows a minimum freezing equimolar mixture at 494 K, a continuous solid solution in equilibrum with liquid phase and an eutectic mixture (88 molar % of KNO₃) at 380 K. The second one exhibits an invariant at 400 K corresponding to the KNO₃ solid-solid transition, an eutectoid mixture at 10 molar % of KNO₃ and 418 K involving the CsNO₃ solid-solid transition and an eutectic mixture at 60 molar % of KNO₃ and 495 K.