Thermodynamic properties of liquid magnesium-bismuth alloys

Thermodynamic properties of liquid Mg-Bi alloys have been determined, employing galvanic formation and concentration cells. There was a fairly good agreement between data obtained by the two different types of cells. The partial thermodynamic functions exhibit a marked deviation from ideality, which has been interpreted as a consequence of the stable compound Mg₃Bi₂ being formed in the system. The experimental data have been treated according to Krupkowski to give equations for the activity coefficients of magnesium and bismuth. From these equations, together with phase diagram data, the Gibbs free energy of formation of solid Mg₃Bi₂ has been evaluated. A similar treatment also has been applied to literature data for the corresponding Mg-Sb system.     

Thermodynamic properties of liquid cadmium-bismuth-lead-tin alloys

Abstract

The partial molar thermodynamic properties of cadmium in molten Cd-Bi-Pb-Sn alloys have been determined using electrochemical concentration cells. The isothermal integral properties were calculated using the analytical method of Pelton. The value of property estimates based on interpolation of empirical series is discussed.

Résumé

Les propriétés thermodynamiques molaires partielles du cadmium dans l'alliage liquide Cd-Bi-Pb-Sn ont été déterminées par voie electrochimique. La methode de Pelton a été utilisée sur une isotherme pour calculer des propriétés intégrales. La validité des estimés de ces propriétés est discutée en se basant sur l'interpolation des séries empiriques.     

Thermodynamic properties of liquid metallic alloys

Experimental data on the activity of components in concentrated (nondilute) liquid metallic alloys must be approximated by characterizing the alloy’s thermodynamic properties on the basis of logγ/(1 ? x ²) rather than logγ. Here γ and x are, respectively, the activity coefficient and molar fraction of the component in the alloy. In that case, the error in calculating the alloy’s integral thermodynamic characteristics—the mixing energy, the regular function—is reduced.     

Thermodynamic properties of liquid manganese-silicon alloys

Vapor pressure measurements have been made on twenty two manganese-silicon alloys in the liquid state, at temperatures between 1400 to 1900 K, using a torsion-effusion technique. The thermodynamic properties of the system have been calculated from the observed vapor pressures of manganese over the alloys at 1700 K. The activities of the components show very strong negative deviations from ideality and the heats of forma-tion are markedly exothermic. Excess free energies evaluated from the vapor pres-sures have been combined with the calorimetrically measured heats of formation, avail-able in the literature, to obtain the excess entropies of mixing which are found to be moderately negative. The present results are assessed with respect to the existing phase equilibria and other thermodynamic data for the solid and liquid states. Among the fac-tors influencing the properties of these alloys, a tendency to form covalent linkages in the liquid state appears most significant. Nazir Ahmad, formerly Research Student/Research Fellow, Department of Physical Metallurgy and Science and Materials, University of Birmingham     

The diffusivity of oxygen in liquid copper-lead alloys

The oxygen diffusivity in liquid copper-lead alloys at 1403 K (1130‡C) was measured us-ing the electrochemical cell: Ni-NiOJZrO₂(+CaO)/O in liquid Cu-Pb alloy(I)/ZrO₂(+CaO)/O in liquid Cu-Pb alloy(II). Oxygen in liquid Cu-Pb alloy(I) was transferred to the right by applying a preselected voltage between the two liquid Cu-Pb alloys. The oxygen diffusivity in liquid Cu-Pb alloy(I) was calculated from the emf change with time between the Ni-NiO and liquid Cu-Pb alloy (I) electrodes. The results were: D_o (in pure Cu) = 8.14 (^+0.70 _-0.43) × 10⁵ cm²/s, D_o (in Cu-25 at. pct Pb) = 11.4(^+0.4 _-0.6) × 10^-5 cm²/s, D_o (in Cu-50 at. pct Pb) = 12.9(^+1.9 _-1.5) × 10^-5 cm²/s, D_o (in Cu-75 at. pct Pb) = 11.0(^+2.4 _-1.2) x 10^-5 cm²/s, D_o (in pure Pb) = 26.3(^+4.8 _-3.7) × 10^-5 cm²/s. It was found that the oxygen diffusivity in liquid copper-lead alloys did not change dras-tically over the entire composition range, in contrast with that reported by other investi-gators for liquid copper-nickel alloys. The oxygen diffusivity in pure liquid lead agreed with the results of our previous work using an FeO-Fe₃O₄ mixture as a sink for oxygen.     

The diffusivity of oxygen in liquid copper-lead alloys

The oxygen diffusivity in liquid copper-lead alloys at 1403 K (1130° C) was measured using the electrochemical cell: Ni−NiO/ZrO₂(+CaO)/O in liquid Cu−Pb alloy(I)/ZrO₂(+CaO)/O in liquid Cu−Pb alloy (II). Oxygen in liquid Cu−Pb alloy (I) was transferred to the right by applying a preselected voltage between the two liquid Cu−Pb alloys. The oxygen diffusivity in liquid Cu−Pb alloy(I) was calculated from the emf change with time between the Ni−NiO and liquid Cu−Pb alloy (I) electrodes. The results were: It was found that the oxygen diffusivity in liquid copper-lead alloys did not change drastically over the entire composition range, in contrast with that reported by other investigators for liquid copper-nickel alloys. The oxygen diffusivity in pure liquid lead agreed with the results of our previous work using an FeO−Fe₃O₄ mixture as a sink for oxygen.     

Thermodynamic properties of ternary liquid Cu-Mg-Ni alloys

Magnesium vapor pressures were determined over ternary Cu-Mg-Ni alloys along three isopleths withx _Cu/x _Ni = 2.0, 1.0, and 0.5 using an isopiestic method. Data points were obtained between approximately 20 and 90 at. pct magnesium in the temperature interval from 1050 to 1350 K. Partial thermodynamic properties of magnesium were derived for the liquid phase, and integral Gibbs energies of formation were computed by a Gibbs-Duhem integration. The composition dependence of the activities at 1173 K is shown for the three sections investigated. The experimental integral Gibbs energies of mixing for liquid alloys are compared with the values calculated from binary data by a geometrical formalism.     

Thermodynamic properties of solid and liquid neodymium-magnesium alloys

The thermodynamic properties of liquid and solid magnesium-rich magnesium-neodymium alloys are determined by the electromotive force method using its classic equilibrium (I) and dynamic (II) versions. The results obtained by both versions agree within the limits of experimental error and clearly reveal phase transformations in the alloys, including the steplike decomposition of supersaturated solid solutions.     

Thermodynamic properties of liquid alloys of gadolinium with silicon

Powder Metallurgy and Metal Ceramics - Partial heats of mixing for gadolinium and silicon in the binary system Gd–Si are measured by means of a high-temperature isoperibolic calorimeter in...     

Thermodynamic properties of liquid alloys of the Ni-Hf system

By the method of calorimetry in isoperibolic conditions are determined integral and partial mixing enthalpies of liquid alloys of the Ni-Hf system at 1770 ± 5 K. Defined that liquid Ni-Hf alloys are formed with allocated large quantity of heat. The analysis of own and literary data has allowed to establish for mixing enthalpies of binary Ni-Hf liquid alloys dependence on temperature. With use of the Schröder equation are calculated the activities of studied alloys components from co-ordinates of liquidus line of the phase diagram of this system. Between calculated and experimentally established values of melts components activities of the Ni-Hf system is observed only qualitative consent. Are also calculated ΔG and ΔS of liquid Ni-Hf alloys.     

Thermodynamic properties of liquid tin-tellurium alloys at high temperature

Electromotive force measurements on galvanic cells have been performed in order to obtain the tin activity in liquid tin-tellurium alloys in the composition range 0.200 <x _Te < 0.750 and between 673 and 1123 K. The position of some liquidus points, determined by emf measurements, was verified by differential thermal analysis. Moreover calorimetric measurements were made at 873 K. By graphical integration of the Gibbs-Duhem relationship, partial molar Gibbs energy and enthalpy changes, ΔG _Te and ΔH _Te were obtained. The integral thermodynamic properties ΔH _M,TΔS _M and ΔG _M were also calculated at 1100 K. From these thermodynamic values and the variations of viscosity and electrical resistivity given in the literature and according to the essentially covalent nature of the bonding in the solid SnTe, we have qualitatively investigated the dependence of the nature and the evolution of the interactions with the temperature in the neighborhood of the compositionx _Te = 0.500. J. Rakotomavo, who is preparing his thesis     

Thermodynamic properties of liquid alloys of germanium with d-transition metals

We present the results of a calorimetric investigation of the enthalpies of mixing in Ge-Zr and Ge-Nb systems at 1973 K in the range 0 to 22 at.%. We show that alloy formation in these systems is accompanied by a large exothermic effect. This is connected with the large influence of binary intermetallic compounds in the Ge-Zr and Ge-Nb systems.Taras Shevchenko National University. Translated from Poroshkovaya Metallurgiya, Nos. 7–8, pp. 76–79, July–August, 1996.     

Copper-scandium system: Thermodynamic properties of intermetallics and liquid alloys

Thermodynamic simulation of the binary Cu-Sc system is performed for a wide temperature range using experimental data on the thermodynamic properties of solid Cu-Sc alloys. The results obtained are used to estimate the thermodynamic functions of mixing and the activities of the components and to determine the composition of melts using an ideal solution model for interaction products. The calculated enthalpies of mixing at 1873 K agree adequately with the experimental data obtained by calorimetry.     

Thermodynamic properties of liquid Al-Mg alloys measured by the Emf method

The thermodynamic properties of liquid Al-Mg alloys containing 0.027 to 95.50 at. Pct Mg were determined by measuring the emf, between 973 and 1073 K, of a magnesium concentration cell of the type Mg(l)|MgCl₂-CaCl₂ (eutectic melt, l)|Mg (in Al, l). Special attention has been given to low-magnesium aluminum alloys which are most commonly used in industry and for which definitive thermodynamic data are not reported in the literature. Alloys containing up to 12 at. Pct Mg follow Henry’s law, and the magnesium activity is given by the relation a_MG = 0.88 X_MG at 1073 K. Above 12 at. Pct Mg, the magnesium activity shows a small negative deviation from the ideal solution behavior. The activity of aluminum, however, closely follows the ideal solution behavior up to 75 at. Pct Mg and thereafter it shows a small negative deviation. The emf data have also been used to determine the free energy, entropy, enthalpy, and excess free energy for liquid Al-Mg alloys.     

Thermodynamic parameters of liquid gold-aluminum alloys

Thermodynamic activities and, enthalpies for Au−Al alloys have been measured by Knudsen-cell mass spectrometry, independently using closely similar techniques in laboratories in Vienna and Strathclyde. The results are consistent and indicate, for Au rich alloys, gold activities with positive deviations from Raoult ideality. This is in disagreement with EMF measurements of Au activity previously reported; the results also indicate endothermicities (of ∼ 38 kJ/mol at _x Al ∼ 0.5) that are some 5 to 6 kJ/mol larger than those indicated by the EMF measurements.     

Thermodynamic properties of magnesium-lead alloys

Magnesium activities in liquid magnesium-lead alloys have been measured with electromotive force cells over the temperature range 745 to 868 K and over the mole fraction range 0.03 <X _Mg<0.50. The exper imental data were used to evaluate the parameters in the empirical temperature-composition relationship proposed by Krupkowski for describing the activity coefficients. Values generated from the Krupkowski formulae were utilized with data for liquidus compositions to evaluate the free energies of formation of the solid intermediate phases and compared with available experimental data for Mg₂Pb.     

Thermodynamic properties of Mn-Si alloys

All available literature data on the thermodynamic properties of Mn-Si alloys are analyzed. Optimized concentration dependences of the thermodynamic functions of mixing are obtained.     

Thermodynamic measurements in liquid tin-tellurium alloys

Electromotive force measurements on galvanic cells have been performed in order to obtain the tin activity in liquid tin-tellurium alloys in the composition range x_Te = 0.756 to 0.978 and between 673 and 913 K. The partial enthalpy and entropy of solution of tin in tellurium were deduced from these results. The position of the liquidus in the vicinity of the eutectic was specified by emf measurements and by differential thermal analysis. The existence of strong interactions in the liquid state and the existence of the compound SnTe in the solid state strongly suggest that short range order subsists in liquid alloys. A simple interaction model has allowed us to interpret correctly the experimental results in the investigated concentration range.