Thermodynamic and structural investigations of liquid magnesium-thallium alloys

The thermodynamic and microscopic structure of MgTl liquid alloy at 923 K has been studied by using regular associated solution model. The free energy of mixing, heat of mixing, entropy of mixing, activity, concentration fluctuations in long-wavelength limit S_CC(0) and the Warren-Cowley short-range parameter α₁ have been determined. The analysis suggests that this alloy is of a moderately interacting nature. The theoretical analysis reveals that the pairwise interaction energies between the species depend on temperature and there is a tendency of unlike atoms pairing (Mg-Tl) in liquid MgTl alloys at all concentration. The observed asymmetry in the properties of mixing of MgTl alloy in molten state is successfully explained by assuming MgTl complex on the basis of regular associated solution model.     

Topological investigations of binary and ternary mixtures: excess isentropic compressibilities

The speed of sound, U_ij 1,3-dioxolane (D) in binary mixtures (ij) with benzene, cyclohexane, n-hexane or n-heptane and U_ijk for 1,3-dioxolane in ternary mixtures (ijk) with the same hydrocarbons have been measured as a function of composition at 298.15 K. The observed data have been utilised to evaluate excess isentropic compressibility of binary, (κ_s^E)_ij and ternary (κ_s^E)_ijk mixtures using density and speed of sound values of the binary and ternary mixtures. The Moelyn-Huggins concept of interaction between the molecular surfaces of the components of a binary mixture [Polymer 12 (1971) 389] has been extended to evaluate excess isentropic compressibility of the studied binary and ternary mixtures. It has been observed that κ_s^E values predicted by a graph-theoretical approach using connectivities of third degree for binary mixtures compare reasonably well with their corresponding experimental values and κ_s^E for ternary mixtures are of the same sign and order of magnitude.     

Thermodynamic investigations on the component dependences of high-entropy alloys

In the present research, a study on the thermodynamical properties of the quinary Co–Cu–Cr–Fe–Ni high-entropy alloys and ternary Ca–Sb–Yb is carried out by the models Kohler, Chou’s general solution method (GSM) and Muggianu. The dependences of composition variation on thermodynamic properties, such as enthalpy of mixing of Co–Cu–Cr–Fe–Ni alloys in simple FCC phase are investigated at the temperatures 1273, 1373, and 1473 K. Moreover, a comparison between the results of the three models and those of other theoretical models shows good mutual agreement.     

Why do ternary compounds exist? — Thermoanalytical investigations on binary systems of metal chlorides

Ternary chlorides are stable if they can be formed from each pair of the other compounds in a system with a gain in energy. Especially, the energy of formation from the two adjacent compounds, the energy of synproportionation must be negative. At 0 K this condition is fulfilled, if (lattice) enthalpy is won. At higher temperature also theT·S-term of the Gibbs-Helmholtz-equation can be of significance: a loss in H must be compensated by a gain inT·S, if a (high-temperature) compound shall exist.This conception was proved experimentally on systems ACl/MCl₂ and ACl/LnCl₃(Ln=Lanthanides). By DTA and X-ray powder patterns the phase diagrams of the pseudobinary systems were elucidated, to yield the stoichiometry and structures of the existing compounds. By solution calorimetry the formation enthalpies at room temperature from the binary parent-compounds were determined. Measurements with a galvanic cell for solid electrolytes at temperatures higher than 300 °C yield the free enthalpies and entropies of synproportionation.The main result of these measurements is, that compounds with isolated coordination polyhedra (K₂CoCl₄=tetrahedra; Rb₃LaCl₆=octahedra) can have a sufficiently high gain in entropy to be stable at temperatures > 0 K.

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Zusammenfassung Ternäre Chloride sind stabil, wenn sie sich aus allen Paaren der restlichen in einem System existierenden Verbindungen unter Energiegewinn darstellen lassen. Insbesondere muß die Bildungsenergie aus den beiden Nachbarverbindungen, die Synproportionierungsenergie, netativ sein. Bei 0 K ist diese Bedingung erfüllt, wenn dabei (Gitter-) Enthalpie gewonnen wird. Bei höheren Temperaturen kann auch derT·S-Term der Gibbs-Helmholtz-Gleichung ausschlaggebend werden: ein Verlust an H muß durch einen genügend großen Gewinn anT·S kompensiert werden, damit eine (Hochtemperatur-) Verbindung existieren kann.Dieses Konzept wurde experimentell an Systemen ACl/MCl₂ und ACl/LnCl₃ (Ln=Lanthanoid) bewiesen. Durch DTA und Röntgenpulveraufnahmen wurden die Phasendiagramme der pseudobinären Systeme erstellt, um Zusammensetzung und Strukturen der existierenden Verbindungen zu ermitteln. Mittels Lösungskalorimetrie wurden die Bildungsenthalpien bei Raumtemperaturen aus den binären Ausgangsverbindungen gemessen. Messungen mit einer galvanischen Zelle für Festelektrolyte bei Temperaturen >300 °C lieferten die freien Enthalpien und Entropien für die Synproportionierungsreak-tionen. Als wichtigstes Resultat ergab sich, daß Verbindungen mit isolierten Koordinationspolyedern (K₂CoCl₄=Tetraeder; Rb₃LaCl₆=Oktaeder) einen so großen Entropiegewinn aufweisen, daß sie bei hohen Temperaturen stabil sein können.

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, . . , () . - T·S , H T·S . l/l₂ ACl/LnCl₃, Ln — . . . 300° . , (₂l₄ — , RbLaCl₆ — ) , .

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Support by the Deutsche Forschungsgemeinschaft and Fonds der Chemischen Industry is gratefully acknowledged.     

Thermodynamic excess properties of ternary alcohol-hydrocarbon systems. Simplified method for predicting enthalpies from binary data

Two general equations for estimation of excess enthalpies of ternary systems consisting of an alcohol and two hydrocarbons from observed excess properties of the various binary combinations have been developed. The first expression is based on the Kretschmer-Wiebe association model and takes the form $$\Delta \overline H _{ABC}^{ex} = h_A x_A K_A (\phi _{A1} - \phi _{A1}^o ) + Q_{ABC}$$ where $$\begin{gathered} Q_{ABC} = (x_A + x_B )(\phi _A + \phi _B )(\Delta \overline H _{AB}^{ex} )_{phys}^ \bullet + (x_A + x_C )(\phi _A + \phi _C )(\Delta \overline H _{AC}^{ex} )_{phys}^ \bullet \hfill \\ + (x_B + x_C )(\phi _B + \phi _C )(\Delta \overline H _{BC}^{ex} )_{phys}^ \bullet \hfill \\ \end{gathered}$$ \((\Delta \overline H _{ij}^{ex} )_{phys}^ \bullet\) represents the physical interactions in each of the individual binary systems, and the term involving φ _A1 ^o represents the chemical contributions (caused by self-association) to the excess enthalpies of mixing. The second predictive expression is based on the Mecke-Kempter association model and is given by $$\Delta \overline H _{ABC}^{ex} = - h_A x_A [In(1 + K_A \phi _A )/K_A \phi _A - In(1 + K_A )/K_A ] + Q_{ABC}$$ where the first term (contained within brackets) represetns the chemical contributions to the enthalpies of mixing. The predictions of both expressions are compared with experimental data for the excess enthalpies of six ternary systems.     

Thermodynamic investigation of the binary and ternary complexes involving 1-aminocyclopropane carboxylic acid with reference to plant hormone

Complex formation equilibria of 1-aminocyclopropane carboxylic acid (ACC) and 3,3-bis(1-methylimidazol-2-yl) propionic acid (BIMP) with metal ions Cu²⁺, Ni²⁺, Co²⁺, Zn²⁺, Mn²⁺ and Fe²⁺ were investigated. ACC forms 1:1 and 1:2 complexes in addition to the hydrolysed form of the 1:1 complex, except in the case of Mn²⁺ and Fe²⁺, where the hydrolysed complex is not formed. BIMP forms 1:1 and 1:2 complexes in addition to the hydrolsed form of the 1:1 complex in the case of Mn²⁺ and Cu²⁺, however the hydrolysed complex is not detected for Ni²⁺, Co²⁺, Zn²⁺ and Fe²⁺. The concentration distribution diagrams of the complexes were determined. The Fe²⁺-complex with BIMP is exothermic and the thermodynamic parameters were calculated. The effect of organic solvent on the acid dissociation constants of 1-aminocyclopropane carboxylic acid (ACC) and 3,3-bis(1-methylimidazol-2-yl) propionic acid (BIMP) and the formation constants of Fe²⁺ complexes were investigated. Fe²⁺ forms a mixed-ligand complex with ACC and BIMP with stoichiometric coefficients 1:1:1. The formation constant was determined. The ternary complex is enhanced by back donation from the negatively charged 1-aminocyclopropane carboxylate to the π-system of BIMP. From the concentration distribution diagram, the ternary complex prevails in the physiological pH range.      

Spectrophotometric investigations of binary and ternary complexes of Cd(II), methylthiourea and halide ions in aqueous solution

The results of spectrophotometric investigations of mixed-complex formation equilibria of Cd(II), methylthiourea (MeTU) and halide ions (Cl⁻, Br⁻ and I⁻) in aqueous solution have been reported. The formation of binary and ternary complexes has been found. The values of the equilibrium constants (log units) for the reaction MA₂+MB₂⇌2MAB, are 1.03±0.10, 1.17±0.12 and 1.34±0.08 for [CdMeTUCl]⁺, [CdMeTUBr]⁺ and [CdMeTUI]⁺, respectively. It was found that the stability of ternary complexes depends on the values of the normal redox potential of halide ions.     

Thermodynamic properties of vanadium-tellurium alloys

Tellurium vapor pressures of vanadium-tellurium alloys were determined in the range of the NiAs-derivative structures between 765 and 1365 K and between 54 and 66.7 at.% Te by an isopiestic method. The partial molar thermodynamic quantities of tellurium were derived; they indicate the appearance of a miscibility gap below about 825 K with a critical point around 64.7 at.% Te. The solidus line was estimated between 773 and 1273 K from the tellurium activities and the experimentally determined liquidus line; good agreement was found between the calculated values and those obtained from differential thermal analysis.     

Thermodynamic properties of cobalt-selenium alloys

Vapor pressures of selenium in cobalt-selenium alloys were determined by an isopiestic method between 600 and 1000 °C and between 52 and 66.6 at % Se. Activities of selenium were evaluated according to three methods taking into account the complexity of the selenium vapor. For the nonstoichiometric Co_1?x Se phase with NiAs-type structure a statistical model was applied. Activities and partial molar enthalpies of selenium derived by assuming random distribution of cobalt atoms and cobalt vacancies in the 001/2-layers of the NiAs-lattice are in very good agreement with the experimental values. The interaction energy between cobalt vacancies was found to be 7780 cal/g-atom.     

The estimation of the thermodynamic properties of ternary alloys from binary data using the shortest distance composition path

A new composition path, X_i-X_j=constant, is suggested for the semi-empirical calculation of the thermodynamic properties of ternary ‘substitutional’ solutions from binary data, when the binary systems show deviations from the regular solution model. A comparison is made between the results obtained for integral and partial properties using this composition path and those calculated employing other composition paths suggested in literature. It appears that the best estimate of the ternary properties is obtained when binary data at compositions closest to the ternary composition are used.     

Determination of niobium and tantalum in binary alloys and zirconium alloys

Recent developments in the metallurgy of niobium, tantalum and zirconium have necessitated provision of analytical procedures for determining niobium and tantalum in the presence of each other and in the presence of zirconium. For this purpose, absorptioinetric procedures based on the formation of yellow coloured complexes, between pyrogallol and niobium or tantalum, have been critically examined. Direct absorptiometric procedures are described, which are suitable for determining niobium or tantalum in the range 2 to 7%; when either of these metals exceeds 7%, differential absorptiometric procedures are recommended. Corrections must lie made for absorption due to the presence of other metals which form complexes with pyrogallol. In tlie determination of niobium or tantalum up to 5%, the precision of the method is about ±0.05%. About 12 determinations can be made in a day, by one analyst.     

Structural investigations of ternary lanthanoid and uranium nickel phosphides

The new compound LaNi₅P₃ was prepared by reaction of the elemental components in a tin flux. It crystallizes with the orthorhombic LaCo₅P₃-type structure, space groupCmcm, and the lattice constantsa = 3.642(1), b = 11.716(2), c = 11.494(3). Its structure was refined from single-crystal X-ray data toR = 0.070(759Fvalues, 16 variables). UNi₂P₂ with ThCr₂Si₂-type structure was prepared for the first time. The crystal structures of the ThCr₂Si₂-type compounds LaNi₂P₂ (R = 0.016, 190 F's, 11 variables) and CeNi₂P₂ (R = 0.015, 199 F's, 11 variables) were refined from single-crystal X-ray data. Chemical bonding in the ThCr₂Si₂-type compounds is discussed.     

Thermodynamic characterization of ternary solutions of uncharged polymers

The thermodynamic interactions in aqueous solutions of uncharged polymers were studied. Using a gel-deswelling method, the water activities (chemical potentials) in binary and ternary (two polymers in one solvent) solutions of methylcellulose (MC), polyvinyl alcohol (PVA) and polyvinyl pirrolidone (PVP), respectively were determined at various polymer volume fractions (1.0 × 10⁻² < v₂ < 1.0 × 10⁻¹). On the theoretical basis of the Flory–Huggins approximations, the relevant solvent–segment (χ₁₂ or χ₁₃) and segment–segment pair interaction parameters (χ₂₃) have been calculated.

The solvent activity curves (ln a₁ versus polymer volume fraction) can be well described by a polynomial of third-degree in both the binary and the ternary solutions of the polymers. The solvent–segment interaction parameters exhibit a slight dependence on the polymer concentration. For each binary solution, the χ₁₂−v₂ function can be fitted by a straight line wich has a small positive slope. In the mixtures of two polymers, the values of the segment–segment (χ₂₃) interaction parameters were close to zero or sligthly negative (χ₂₃ 0 ± 0.03), indicating that under the studied conditions, the polymers in the ternary solutions are compatible.     

Potentiometric studies of binary and ternary complexes of amoxycillin

The formation equilibria for the binary complexes of copper(II), nickel(II), cobalt(II) and zinc(II) with amoxycillin (Amx) and for the ternary complexes M(Arm)(Amx), where Arm refers to aromatic amines, namely 2,2′-dipyridyl or 1,10-phenanthroline, were investigated by a potentiometric technique. The protonation constants of amoxycillin and conditional stability constants of the formed complexes were determined at 25° (=0.1M NaNO₃). Probable mode of chelation with amoxycillin is discussed.     

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.     

Chromatographic study of adsorption from binary and ternary solutions

Adsorption of benzene, anisole, and nitrobenzene on hydroxylated silica gel from binary and ternary solutions (adsorbate--n-hexane and adsorbate--n-hexane--terahydrofuran) was studied by HPLC. The equation that describes the adsorbate retention as a function of its concentration in binary and ternary solutions was proposed. The equation makes it possible to calculate the adsorption isotherms and adsorption equilibrium constants directly from chromatograms using the retention parameters and equilibrium concentrations of the adsorbate in the mobile phase.     

二元及三元离子交换体系的统计热力学

本文用统计热力学方法对二元及三元离子交换体系进行了研究,得到了修正选择系数与交换剂组成关系的理论表达式,并得到二元交换体系的交换剂组分活度系数与组成的关系式,即Kielland公式。