Thermodynamic properties of Eu-Sn melts

Partial and integral mixing enthalpies of melts of the Eu-Sn system were determined by calorimetry at 1300 (1250) K in the concentration intervals 0 < x _Sn < 0.16 and 0.7 < x _Sn < 1. It was found that the first partial mixing enthalpies of Sn and Eu were −215.6 ± 10.6 and −161.2 ± 7.6 kJ/mol, respectively. The thermodynamic properties of the Eu-Sn alloys were modeled using the theory of ideal associated solutions over a wide interval of concentrations and temperatures. In was found that the activities of components exhibit strong negative deviations from Raoult’s law. At minimum, the calculated integral Gibbs energies of mixing reach −43.4 kJ/mol at x _Sn = 0.48; ΔG ^ex = −36 kJ/mol, ΔS ^ex = −22 J/(mol K).     

Thermodynamic properties of Al-Y system melts

The thermochemical properties of Al-Y melts were determined by isoperibolic calorimetry. It was established that the minimal value of integral mixing enthalpies is equal to −40.8 + 0.4 kJ/mol at 1770 K and x _Y = 0.41. The thermodynamic properties of liquid alloys were modeled by the developed procedure using the coordinates of a liquidus line in the phase diagram of the Al-Y system, and by the theory of ideal associated solutions. The component activities exhibit high negative deviations from the Raoult law. The Gibbs energies of mixing of Al-Y melts have a minimum of −30.6 kJ/mol at x _Y = 0.48.     

Thermodynamic properties of melts of the binary Ag(Au)-Sm systems

The enthalpies of mixing for liquid alloys of the Ag-Sm system are determined by isoperibolic calorimetry at 1450–1506 K in the 0.46 < x _Sm < 1 range of concentrations. The partial and integral enthalpies of mixing for melts of the Ag-Sm system are obtained over the whole range of concentrations. The activities of components and the entropy of mixing in melts of the Ag-Sm system at 1506 K are calculated using a model of ideal associated solutions (IAS). The partial and integral enthalpies of mixing for melts of the Ag-Sm system, the activities of the components, and the molar fractions of associates in them are calculated using the IAS model. It is concluded that the thermodynamic activities of components in melts of the Ag (Au)-Sm system at 1506 K exhibit great negative deviation from the ideal behavior, and the enthalpies of mixing indicate there are considerable exothermal effects.     

A calorimetric study and modeling of the enthalpy of mixing of Cu-Fe-V melts

The partial enthalpy of mixing of vanadium in three-component Cu-Fe-V melts was studied at 1873 K along sections with constant x _Cu/x _Fe ratios of 3, 1, and 1/3 over the composition range x _V = 0–0.55 by high-temperature isoperibolic calorimetry. The Muggianu-Redlich-Kister model was used to describe the concentration dependence of the integral enthalpy of mixing of Cu-Fe-V melts over the whole concentration triangle. The contribution of ternary interaction to the integral enthalpy of mixing of Cu-Fe-V melts was calculated.     

Thermodynamic properties of alloys of the Ni-Sc and Ni-Y systems

Partial and integral enthalpies of mixing for Ni-Y melts at 1775 K (0 < x _Y < 0.34), 1850 K (0.72 < x _Y < 1) and Ni-Sc at 1880 K (0 < x _Sc < 0.35, 0.51 < x _Sc < 1) are determined by means of calorimetry. Thermodynamic properties of liquid and solid alloys and phase diagrams of Ni-Sc(Y) systems in wide ranges of concentration and temperature are modeled using the ideal associated solution theory. It is found that the activities of components exhibit strong negative deviations from the Raoult’s law.     

Thermodynamic properties of Ni-Ga melts

The partial mixing enthalpies of the components (Δ_m $ \bar H $ \bar H _i ) of the Ni-Ga melts were measured using the high-temperature isoperibolic calorimetry at 1770 ± 5 K in wide concentration interval. The limiting partial mixing enthalpy of gallium in a liquid nickel (Δ_m $ \bar H $ \bar H _Ga^∞) is −95.5 ± 19.8 kJ mol⁻¹, and similar function of nickel in liquid gallium (Δ_m $ \bar H $ \bar H _Ni^∞) is −74.5 ± 16.4 kJ mol⁻¹. The integral mixing enthalpy of liquid alloys of this system was calculated from partial enthalpies for the whole concentration area (Δ_m H _min = −32.1 ± 2.7 kJ mol⁻¹ at x _Ni = 0.5). The Δ_m H value of liquid nickel-gallium alloys independence of the temperature is confirmed. Enthalpies of formation of liquid (Δ_m H) phases of Ni-Ga system were compared with ones for solid (Δ_f H) phases of this system. An analysis of d-metals influence on formation energy of Ga-d-Me melts was made using the values of Δ_f H for intermediate phases of these systems. The article was translated by the authors.     

Thermodynamic properties of alloys of the Al-Co and Al-Co-Sc systems

Enthalpies of mixing for melts of the binary Al-Co system at 1870 K in the range 0 < x _Co < 0.25, and at 1620 K, 0 < x _Co < 0.12, are investigated by means of isoperibolic calorimetry. Enthalpies of mixing for melts of the ternary Al-Co-Sc system are investigated at 1870 K for sections Al_{0.75(1 ? x)}Co_{0.25(1 ? x)}Sc _x , 0 < x < 0.024, and Al_{0.88(1 ? x)}Co_{0.12(1 ? x)}Sc _x , 0 < x < 0.044. Using the literature data on the enthalpies of mixing for liquid and solid alloys, the activities of melt components, and the phase diagram of the Al-Co system, the thermodynamic properties of liquid and solid alloys of the Al-Co system over a wide range of temperatures and compositions are calculated using a software package of our own design, based on the model of ideal associated solutions (IAS). The enthalpies of mixing and the liquidus surface of the phase diagram of the ternary Al-Co-Sc system over the interval of concentrations are estimated by modeling with data on binary boundary subsystems. All of the components of both the binary Al-Co and ternary Al-Co-Sc systems tend to interact with one another quite strongly: ΔH _min(Al-Co) = ?32.5 kJ/mol at x _Co = 0.44; ΔH _min(Al-Co-Sc) = ?46 kJ/mol for Al_0.4Co_0.3Sc_0.3 (estimated).     

The enthalpy and heat capacity characteristics of the water-N,N-dimethylpropyleneurea system

A variable-temperature isothermic-shell calorimeter was used to measure the heat effects of dissolution of N,N-dimethylpropyleneurea (DMPU) in the water-N,N-dimethylpropyleneurea system at 298 and 313 K over the interval of compositions x ₂ = 0−0.1 mole fractions. The partial molar enthalpies of mixture components and the enthalpies and heat capacities of mixing were calculated. The results were compared with the data on water-amide systems. The exothermic effect of mixing of nonelectrolytes with water was found to increase in the series dimethylformamide < dimethylacetamide ∼ DMPU < hexamethylphosphorotriamide (HMPT). The McMillan-Mayer formalism was used to determine the enthalpy and heat capacity parameters of pair and three-particle interactions between DMPU molecules in water. The behavior of DMPU in water was to a substantial extent determined by hydrophobic interactions between nonpolar molecule moieties. This interaction was, however, noticeably weaker than in solutions of HMPT.     

Enthalpies of mixing of Al-Ni-La ternary alloys

Partial (for nickel) and integral enthalpies of mixing of liquid alloys of the Al-Ni-La ternary system of three radial sections with a constant ratio of molar fractions of aluminum and lanthanum x _Al/x _La = 0.3/0.7 at 1770 ± 5 K and 0.5/0.5 and 0.8/0.2 at 1870 ± 5 K up to molar fractions of nickel in ternary alloys of approximately 0.5–0.6 are studied by means of high-temperature calorimetry in isoperibolic mode. It is found that the enthalpies of mixing of the melts are essentially exothermic values. Based on the energetics of alloy formation of this ternary system, it is concluded that the main contribution is made by interaction between the components of melts of the boundary Ni-Al binary system.     

Thermodynamic properties of melts of Mn-Sc(Y, Ln) systems

Partial and integral mixing enthalpies of melts of binary systems Mn-Sc and Mn-Y at 1873 and 1830 K, respectively, are determined by calorimetry. It is found that the minima of the mixing enthalpies are ?7.1 ± 0.4 and -3.2 ± 0.2 kJ/mol at x _Mn = 0.60 and 0.61, respectively. The initial partial mixing enthalpies of Sc and Y are ?33.2 ± 2.1 and ?16.6 ± 0.8 kJ/mol, respectively. The thermodynamic properties of melts of binary Mn-Sc(Y) systems are calculated using the ideal associated solution (IAS) model. It is found that the activities of the components exhibit slight negative deviations from the ideal solutions, and the excess Gibbs energies reach ?3.0 and ?1.6 kJ/mol, respectively.     

Enthalpie De Formation Et De Melange De Phosphoapatites Calco-Cadmiees Chlorees

Calcium–cadmium chlorapatites solid solutions with the general formula Ca_10–xCd_x(PO₄)₆Cl₂,1≤x≤10, were prepared by solid state reaction and characterized by X-ray diffraction, infrared spectroscopy and chemical analysis. Using an isoperibol calorimeter, their enthalpies of solution in 9 mass% nitric acid were measured. In order to determine the enthalpies of formation and enthalpies of mixing, thermochemical cycles were proposed and complementary experiences were performed. The results obtained show a decrease of the enthalpy of formation with the amount of cadmium introduced in the lattice. The variation of mixing enthalpy vs. x=Cd/(Cd+Ca) shows a maximum at about x=0,4. This could be explained by the existence of two cationic sites in the phosphoapatite structure. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermodynamic Properties of Alloys of the Binary Bi—Yb System

The thermochemical properties of melts of the binary Bi—Yb system were studied by the calorimetry method over the concentration ranges 0 < x_Yb < 0.43 at 1000–1270 K and 0.8 < x_Yb < 1 at 1100–1140 K. It was shown that significant negative heat effects of mixing are characteristic features for these melts. A range 0 < x_Yb < 0.19 of the Bi—Yb phase diagram was investigated by the DTA method. Using the regular associated solution (RAS) model, the activities of components, Gibbs energies and the entropies of mixing in the alloys, and the phase diagram of this system were calculated. They agree with the data from literature.     

Standard enthalpy of formation of lanthanum oxybritholites

Lanthanum-bearing silicate-oxyapatites or britholites, Ca_10–xLax(PO₄)_6–x(SiO₄)_xO with 1≤x≤6, have been synthesized by solid state reaction at high temperature. They were characterized by X-ray diffraction and IR spectroscopy. Using two microcalorimeters, the heat of solution of these compounds have been measured at 298 K in a solution of nitric and hydrofluoric acid. A strained least squares method was applied to the experimental results to obtain the solution enthalpies at infinite dilution, and the mixing enthalpy in two steps. In the first step the mixing enthalpy obtained is referenced to the britholite monosubstituted and to the oxysilicate. The mixing enthalpy referenced to the oxyapatite and to the oxysilicate is then extrapolated. In order to determine the enthalpies of formation of all the terms of the solution, thermochemical cycles were proposed and complementary experiments were performed. The results obtained show a decrease of the enthalpy of formation with the amount of Si and La introduced in the lattice. This was explained by the difference in the bond energies of (Ca–O, P–O) and (La–O, Si–O).     

Calorimetric Investigations of the System Pb-Bi-Mg-Sb with Oelsen's Method

The results of calorimetric investigations in the section Pb-Bi_x-Mg_y-Sb_z (mole ratio Bi:Mg:Sb=8:1:1) of the system Pb-Bi-Mg-Sb with Oelsen's method are presented. The constructed space diagram and enthalpy isotherm diagram were used to determine integral mixing enthalpies for the investigated section in the temperature interval 450–1100 K. This revised version was published online in August 2006 with corrections to the Cover Date.     

The thermodynamic characteristics of formation of alloys in the Ge-Ga-Mn and Si-Ni-Al systems

The enthalpies of mixing of ternary system melts were determined by high-temperature calorimetry under isoperibolic conditions. For the Ge-Ga-Mn system, measurements were taken at 1780 ± 5 K along five ray sections with constant ratios between the atomic fractions of germanium and gallium up to a ～0.6 mole fraction of manganese; the x _Ge/x _Ga ratios were 0.8/0.2, 0.7/0.3, 0.5/0.5, 0.3/0.7, and 0.15/0.85. For the Si-Ni-Al system, measurements were taken at 1770 ± 5 K along five ray sections with constant ratios between the atomic fractions of silicon and nickel up to a ～0.6 mole fraction of aluminum; the x _Si/x _Ni fratios were 0.85/0.15, 0.7/0.3, 0.5/0.5, 0.3/0.7, and 0.15/0.85. The formation of melts in these systems was found to be exothermic over the composition range studied. The integral enthalpies of melt formation were maximum along the x _Ge/x _Ga = 0.8/0.2 section in the Ge-Ga-Mn system (?18.8 ± 3.3 kJ/mol) and along the x _Si/x _Ni = 0.5/0.5 section in the Si-Ni-Al system (?67.8 ± 3.4 kJ/mol). An analysis of the isolines of the integral enthalpies of mixing led us to conclude that the Ge-Mn and Ga-Mn binary systems had the strongest influence on the thermodynamic characteristics of melt formation in the Ge-Ga-Mn system, the predominant influence being that of the Ge-Mn binary system. An analysis of the energy characteristics of melt formation in the Si-Ni-Al ternary system showed that the major contribution was made by the interaction of components in the Si-Ni and Ni-Al boundary binary systems, the influence of the Si-Ni system being stronger.     

Thermodynamic characteristics and phase equilibria in the alloys of the Ge–La system

Mixing enthalpies of melts of the Ge–La system have been measured using isoperibolic calorimetry within two concentration ranges. For the first range (0 < x _La < 0.16 at 1520 K and 0.16 < x _La < 0.29 at 1570 K), agreement with the known literature data is observed within the experimental error. The second range (0.78 < x _La < 1 at 1470 K and 0.7 < x _La < 0.78 at 1580 K) has been studied for the first time. The melts are characterized by very strong exothermal effects of mixing, which have almost symmetrical concentration dependence: ΔH? _La ^∞ = ΔH? _Ge ^∞ = ?245 kJ/mol at 1470 K. A thermodynamic optimization of the activities of the components and the phase diagram of the system have been conducted based on the obtained experimental data, using an ideal associated solution (IAS) model.     

Review of the thermodynamic and transport properties of EuBr<Subscript>2</Subscript>–RbBr binary system

Differential Scanning Calorimetry was used to study phase equilibrium in EuBr₂–RbBr binary system. It was established that this system includes two eutectics and three stoichiometric compounds. First of them, Rb₂EuBr₄, decomposes peritectically at 778 K. Second one, RbEuBr₃, undergoes the solid–solid phase transition at 732 K and melts incongruently at 852 K. Third compound, RbEu₂Br₅, melts congruently at 888 K. The composition and temperature values of eutectics were determined as x(EuBr₂) = 0.316; T _eut = 776 K and x(EuBr₂) = 0.797; T _eut = 859 K. Mixing enthalpy was measured by direct calorimetry on the whole composition range. The minimum of the mixing enthalpy occurs around the composition x(EuBr₂) ≈ 0.4. The electrical conductivity of liquid mixtures was also investigated over the whole composition range and measured down to temperatures below solidification. The specific conductance (liquid phase) plotted against the mole fraction of EuBr₂ shows a broad minimum at x(EuBr₂) ~ 0.6. The activation energy for conductivity changes with temperature. Results obtained are discussed in terms of possible complex formation.     

Effect of a metal ion on intramolecular spin exchange in spin-labeled complexes

The characteristic features of intramolecular spin exchange in 14 complexes of Ag^I, Hg^II, Ni^II, Pd^II, Pt^II, Au^III, and Pt^IV with spin-labeled ligands were studied by ESR spectroscopy. The measured values of the exchange integral ‖J‖ and the differences between the enthalpies of the efficient conformations (ΔH) were compared with the electronic polarization (refraction)R _f of the Ni^II, Pd^II, and Pt^II ions and Klopman's rigidity parameters σ_K, which characterize the total polarazibility of the ions and the degree of covalence of the bond between the metal atom and the donor atom of the ligand, respectively. Delocalization of the electron spin density and the efficiency of spin exchange are determined by the relative contributions of the s, p, and d orbitals, which produce the overlap integral of wave functions, ‖J‖, and by the geometric features of the coordination polyhedron, which affect the mutual orientation of the N−O fragments. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2005–2009, October, 1999.     

Excess molar enthalpies for ternary mixtures of (methanol or ethanol + water + tributyl phosphate) at <Emphasis Type="Italic">T</Emphasis> = 298.15 K

Excess molar enthalpies for two ternary mixtures of {x ₁ tributylphosphate (TBP) + x ₂ water + x ₃ methanol/ethanol} were measured at T = 298.15 K and atmospheric pressure using a TAM Air isothermal calorimeter, by mixing methanol or ethanol with binary mixtures of (water + TBP). Excess enthalpies for initial binary mixtures of (water + TBP) were also measured under the same conditions, which showed phase separation at low molar fraction of TBP. Experimental results of the ternary mixtures were expressed with constant excess molar enthalpy contours on Roozeboon diagrams.