Moderate Negative Deviations Research Articles

Термодинамічні властивості і фазові рівноваги в сплавах системи Eu—Pb

Firstthe partial and integral enthalpies of mixing of the melts of the Eu—Pb system were determined at a temperature of 1100—1350 K in everything range the composition by method isoperibolical calorimetry. It was established that of the melts of the Eu—Pb system are formed with the release of a big amount of heat: the minimum H = –51,7  ± 0,8 (at xPb = 0,4). Using the model of ideal associated solutions, all the thermodynamic properties (Gibbs energies, enthalpy and entropy of formation of melts, intermetallic compounds and associates) of the Eu—Pb system were calculated. It turned out that the activity of the components in the melts of this system exhibit moderate negative deviations from ideal solutions. According to the IAR model, the temperature-concentration dependences of the Gibbs energies, enthalpies and entropies formation of melts and intermetallics were calculated, and from them were obtained the coordinates of the liquidus curve of the diagram state of the studied system. As a result, the temperature-concentration dependences of the thermodynamic properties of all phases and the liquidus of the Eu—Pb system are obtained, those a thermodynamic description of this system is made. Keywords: calorimetry, melts, intermetallics, thermodynamic properties, Eu, Pb, model of ideal associated solutions, phase equilibria.

РАВНОВЕСНЫЕ ПОТЕНЦИАЛЫ ОКСИДА СВИНЦА (II) В ЭКВИМОЛЬНОМ РАСПЛАВЕ KCl-PbCl2

The electromotive forces (EMF) of the electrochemical system (GC)Pb|(1-N)·KCl-PbCl2+N·PbO|ZrO2(Y2O3)|O2(Pt) in the concentration range of PbO 0.16-7.32 % mol. were measured at temperatures 776, 821 and 874 K. From the experimental values of EMF activities, coefficients of the activity and basic thermodynamic functions of lead oxide for dilute solutions were calculated. It is shown that PbO activities in the KCl-PbCl2 melt have moderate negative deviations from Raoul's law for ideal solutions. The activity coefficients of PbO at each temperature within the calculation errors are constant, that is, the diluted solutions of PbO in KCl-PbCl2 obey Henry's law. In the studied area of dilute solutions of PbO solvent activity coefficients are constant within the error, and their value is close to 1, as a consequence of the solvent activity within the calculation error will be equal to its molar fraction. This confirms the rule of Kubashevskii-Alcock about the obedience behavior of the solvent KCl-PbCl2 to Raoult's law for ideal solutions. Partial thermodynamic functions of the solvent - melt KCl-PbCl2 and integral thermodynamic functions of the KCl-PbCl2-PbO system are calculated using the standard equations. The interaction of lead oxide with chloride melts is caused by the formation of oxychloride compounds. According to the literature, there is a compound {[Pb2OCl]++Cl-} in the ion melt. The results of x-ray phase analysis show the presence of Pb2OCl2 compound in the frozen electrolyte melt. Using the device LECO ONH836 the concentration of oxygen in the metal lead was determined. It is shown that the oxygen concentration was 0.031 wt. % after the long-term exposure, which also exceeds the values in the Pb-O diagram almost twice.

Measurement of excess functions of binary gas mixtures adsorbed in zeolites by adsorption calorimetry

Adsorption equilibria and heats of adsorption were measured for mixtures of ethylene and ethane on NaX at 298 K. The pure-component isosteric heat of adsorption of ethane increases with loading due to gas-gas interactions; the heat of adsorption of ethylene is approximately constant with loading because of a balance between cooperative interactions and gas-solid energetic heterogeneity. This mixture, which is nearly ideal on carbon, exhibits moderate negative deviations from ideality on NaX. The nonideality is explained by a difference in the polarities of the molecules: ethylene has a quadrupole moment but ethane is nonpolar. The infinite-dilution activity coefficients are unity in the Henry's law region and decrease exponentially to a value of 0.56 at high loading. Regular-solution theory fails to agree with experiment. All three excess functions (free energy, enthalpy, and entropy) are negative; thus, activity coefficients are less than unity and the enthalpy of mixing in the adsorbed phase is exothermic. These results are consistent with an adsorbed solution in which the molecules are segregated into regions of different composition.

Constitution and thermodynamics of Cu‐Y alloys

AbstractThe thermodynamic properties of Cu‐Y alloys were determined between 973 and 1073 K by emf measurements on galvanic cells using CaF2 single crystals as solid electrolytes. Results yield a complete set of thermodynamic functions for the intermetallic phases (Cu), Cu6Y, Cu4Y, Cu7Y2, Cu2Y, and CuY, as well as information on the phase relations. The system is characterized by moderate negative deviations from ideality. A comparison with analogous systems indicates the influence of the electronic structure of the components on thermodynamic functions. The phase relations of the Cu‐Y system were additionally investigated by DTA and X‐ray diffraction.The present results as well as literature data on the thermodynamics and phase diagram of the Cu‐Y system were used as a basis for a thermodynamic optimization of the system using a computer program based on the least squares method. Optimized and experimental data turned out to be in good agreement.

Isobaric Vapor−Liquid Equilibria in the Systems Methyl Ethanoate + Oxolane and Oxolane + Toluene

The vapor−liquid equilibrium at 101.3 kPa has been determined for the binary systems methyl ethanoate + oxolane (tetrahydrofuran) and oxolane + toluene. The binary system methyl ethanoate + oxolane exhibits positive deviations from ideal behavior, while the binary system oxolane + toluene presents moderate negative deviations from ideality. No azeotropes are present. The activity coefficients and boiling point of the solution were correlated with its composition by the Redlich−Kister, Wohl, Wilson, UNIQUAC, NRTL, and Wisniak−Tamir equations.

Adsorption of gas mixtures in micropores: effect of difference in size of adsorbate molecules

Adsorbed solutions of molecules of unequal size (CCl 2F 2) and CO 2 on activated carbon) show negative deviations from ideal mixing. The size effect was studied by molecular simulation of a Lennard—Jones fluid mixture adsorbed in zeolite 13X. The molecules forming the binary mixture are non-polar and have a 2.4 ratio of saturation capacities (the same as CCl 2F 2 and CO 2). In the molecular simulation, adsorption occurs on the energetically homogeneous surface of a spherical shell. Binary adsorption is centered on separate shells with the larger molecule in the inner shell. At high coverage, the simulations yield moderate negative deviations from ideal mixing similar to experimental data. Both molecules can enter the cavity, but adsorbed-phase nonidealities are caused by the exclusion of the larger molecule from part of the micropore space accessible to the smaller molecule. The partial exclusion effect is calculated from the cavity radius and molecular diameters of the adsorbate molecules.

Determination of the sb activity in sb- te melts by solid state EMF measurements

The antimony activity in liquid Sb-Te solutions was measured at 911 K using a solid-state galvanic cell. The measurements indicated nearly ideal solution behavior for Sb-rich compositions and moderate negative deviations for Te-rich compositions NTe > 0.45), consistent with the presence of shortrange order in the melt. The results of this study were shown to be in good agreement with other thermochemical property values for this binary system.

Thermodynamic Investigation of the Pt—Pb Binary Alloys

AbstractThe enthalpy of formation, hf, of the Pt—Pb alloys was measured in the 923–1316 K temperature range with respect to composition by direct reaction calorimetry (drop method) with the help of high temperature Calvet‐type calorimeters. Furthermore we determined also some phase boundaries from the breaks of the hf(x) curves. — The thermodynamic behaviour of the melts is characterized by moderate negative deviations to ideality suggesting some chemical short‐range order (h = −15.88 kJ · mol−1 at 923 K for χPt = 0.53). The associates are very sensible to temperature since the excess heat capacity is positive with a maximum of about 10.2 J · K−1 · mol−1 near χPt = 0.71. Such a behaviour differs strongly from that of the Pd‐Pb system which shows a strongly negative enthalpy of mixing (h = −38.4 kJ · mol−1) without any temperature dependence.

DETERMINATION OF THE GALLIUM ACTIVITY IN THE GALLIUM-INDIUM-ANTIMONY PSEUDOBINARY LIQUID MIXTURE BY A SOLID STATE ELECTROCHEMICAL METHOD

The Ga activity in Gax In1-x Sb liquid mixtures was obtained from emf measurements across a solid electrolyte electrochemical cell. The measured values of the aGa showed moderate negative deviations from ideal behavior and were directly proportional to the Ga mole fraction.

Ultraviolet spectrum of the nitrate ion in molten mixtures of alkali metal nitrates

The effects of composition and temperature on the first ultraviolet band of the nitrate ion in molten mixtures of alkali metal nitrates are described. The energy of the band maximum E is a linear function of mole fraction for NaNO-RbNO and KNO-RbNO mixtures and shows small positive deviations from linearity for LiNO-NaNO, LiNO-KNO, and LiNO-CsNO. The f number shows moderate negative deviations from linearity for all mixtures. With increasing temperatures E decreases and f increases.

The electric conductivity and the activation energy of ionic migration of molten salts and their mixtures

The electric conductivity ( k ), and its variation with temperature, of many molten salts of predominantly ionic character can be represented by a simple exponential equation k = const. x e -C/RT . Deviations from this relation are sometimes found for partially covalent compounds (e. g. ZnCl 2 , PbCl 2 ) where constitutional changes may be expected with change of temperature. The activation energy of ionic migration ( C ) is always smaller than the activation energy of viscous flow. This fact is attributed to the difference in the configurational changes that occur in the two processes. For alkali chloride, C decreases with increasing ratio of anion to cation radius. For electrolytes involving multivalent ions, C is greater than for uni-univalent ones. Increasing amount of covalency of the bonds involved tends to lower C . The conductivities of a number of mixtures of electrolytes (CdCl 2 -CdBr 2 , CdCl 2 PbCl 2 , CdCl 2 -NaCl, CdCl 2 -KCl, PbCl 2 -KCl) were measured over a range of compositions and temperatures. The activation energies of ionic migration and, where possible, the equivalent conductivities were calculated, and the results discussed together with those obtained in other systems by various investigators. In no system so far investigated is the conductivity a linear function of the composition expressed as mole fraction. In systems which give no evidence of complex ion formation in the mixture, the conductivity usually shows moderate negative deviations from additivity (e. g. CdCl 2 -CdBr 2 ). Only one system so far shows a positive deviation from additivity (CdCl 2 -PbCl 2 . Strong negative deviations from additivity are found in systems in which complex ions are likely to exist in the mixtures (PbCl 2 -KCl, CdCl 2 -KCl, CdCl 2 -NaCl). In the systems CdCl 2 -KCl and PbCl 2 -KCl, the conductivity isotherms have minima at all temperatures investigated; in these systems, the phase diagram indicates a congruently melting compound. Additional minima in the conductivity isotherms are found near compositions at which the phase diagram indicates incongruently melting compounds, but only at low temperatures; at higher temperatures, these minima disappear. The activation energies (C ) have maximum values near compositions that correspond to unstable compounds; in this case, C contains part of the energy change involved in the transition from the complex to the simple ions. In some cases, the activation energy ( C ) of the molten systems rises to very high values as the crystallization temperature is approached. This is interpreted as being due to the existence of a high degree of order in the melt just above the melting-point. Further relations between conductivity, and its temperature coefficient, the activation energy of ionic migration and the constitution of the molten salt mixtures are discussed.