M. Gambino

Étude thermodynamique du système ternaire gallium-indium-antimoine

Abstract With a high temperature microcalorimeter the molar excess enthalpies of mixing for liquid gallium-indium-antimony alloys have been measured at 995 K. From these results and those already obtained for the limiting binary alloys we calculated the whole set of thermodynamic functions in this ternary system. The knowledge of the Gibbs free energies of mixing and of the thermodynamic functions of the GaSb-InSb quasi-binary system enabled one to compute the liquidus of the equilibrium phase diagram on the whole concentration range. The agreement between a few published experimental data and calculated points has been found satisfactory.

Thermodynamic properties of gallium + antimony

Abstract With a high-temperature microcalorimeter the molar excess enthalpies H E of liquid gallium + antimony alloys have been measured at 995 K over the entire mole fraction range. Using an indirect drop method, which is more accurate than the classical drop method, we could determine small excess enthalpies and particularly the limiting partial molar excess enthalpies. We find H E ( x = 0.5) = −(260 ± 10) cal th mol −1 , H Ga E.∞ = −(900 ± 30) cal th mol −1 , and H Sb E.∞ = −(85 ± 5) cal th mol −1 . At 978 K we measured the enthalpy of formation of gallium antimonide: ΔH t = −(7300 ± 300) cal th mol −1 . By three different methods we obtained the enthalpy of melting of GaSb; the value (7200 ± 300) cal th mol −1 seems to us most reliable. With all these thermodynamic values and the phase diagram already known we can propose the activities of gallium and antimony at 1000 K. The values already published of these functions are numerous and often divergent. Our calculated results seems to confirm those measured by Chu-Hsi-Hsiung et al .

The germanium-selenium phase diagram

The binary germanium—selenium system was investigated by differential thermal analysis; from the results a temperature-composition diagram was constructed. The existence of the two compounds GeSe and GeSe2 was confirmed. Furthermore, it could be shown that between 920±4 and 939±2 K GeSe transforms to a high-temperature modification which is slightly richer in selenium and decomposes peritectically at 948±2 K. On the germanium-rich side of the system a monotectic equilibrium exists at 1 177±2 K. Two thermal effects, one between 908 and 918 K, the other one at 851±3 K, were shown to be non-equilibrium effects. GeSe and GeSe2 form a eutectic at 856±2 K and 56.0±0.5 at% Se. The congruent melting point of GeSe2 was determined as 1 015±2 K. Between GeSe2 and Se another eutectic exists at 485±1 K and 94.5±0.5 at% Se.ZusammenfassungDas Zweistoffsystem Germanium—Selen wurde mit Hilfe der Differenz-Thermo-Analyse untersucht; aus den Ergebnissen wurde einT-x-Zustandsdiagramm erstellt. Die Existenz der zwei Verbindungen GeSe und GeSe2 wurde bestätigt. Weiters konnte gezeigt werden, daß zwischen 920±4 und 939±2 K GeSe sich in eine Hochtemperatur-Modifikation umwandelt, welche etwas selenreicher ist und bei 948±2 K peritektisch zerfällt. Auf der germaniumreichen Seite des Systems existiert bei 1 177±2 K ein monotektisches Gleichgewicht. Von zwei thermischen Effekten, einem zwischen 908 und 918 K und einem anderen bei 851±3 K, konnte gezeigt werden, daß sie auf fehlendes Gleichgewicht zurückzuführen sind. GeSe und GeSe2 bilden ein Eutektikum bei 856±2 K und 56,0±0,5 At% Se. Der kongruente Schmelzpunkt von GeSe2 wurde zu 1 015±2 K bestimmt. Zwischen GeSe2 und Se existiert ein weiteres Eutektikum bei 485±1 K und 94,5±0,5 At% Se.

Molar heat capacities of cdte, hgte and cdte-hgte alloys in the solid state

Abstract Using a differential scanning calorimeter, the molar heat capacities of the two components HgTe and CdTe and of ten solid alloys of the CdTeHgTe system were measured at constant pressure between 300 K and 523 K. Irregular variations of the C p = φ ( T ) curves of CdTeHgTe alloys suggest the existence of a solid state miscibility gap in this system. The limit of the (solid ↔ solid (1) + solid (2) ) miscibility gap and coordinates of the critical temperature ( χ CdTe ≠ 0.55, T = 455 K) are proposed. From C P data obtained in a single-phase solid region, the excess molar heat capacities ( ΔC P = C p(exp) − C p(calc) ) at 500 K were deduced: the maximum negative excess C P is located at χ CdTe = 0.5.

YbPb intermetallic compounds: diffractometry and heat capacity measurements

Abstract Structures and molar heat capacities of the YbPb intermetallic compounds were determined at different temperatures by using differential scanning calorimetry, X-ray diffraction and metallographic analyses. Formulae and crystal structures of the different compounds (Yb2Pb, possibly Yb5Pb3, YbPb and YbPb3) were confirmed. For the YbPb compound, the crystal structure of the high temperature modification (cI2, W type) was determined. A value of ΔHtrs = + 1.35 ± 0.1 kJ mol−1 for the transformation enthalpy was measured. Negligible or very small homogeneity ranges were observed for the Yb2Pb and YbPb3 compounds. A homogeneity range from 48 to 50 at.% Pb (at 300–550 °C) was determined for YbPb.

Capacite calorifique de l'uree et de quelques melanges eutectiques a base d'uree entre 30 et 140° C

Abstract The temperature and melting enthalpy of urea and of the following eutectic mixtures have been previously determined by differential thermal analysis tb]5,3 r ]CO(NH 2 ) 2 + NaCl c ]CO(NH 2 ) 2 + NaI c ]CO(NH 2 ) 2 + NaNO 3 r ]CO(NH 2 ) 2 + NaBr c ]CO(NH 2 ) 2 + KI c ]CO(NH 2 ) 2 + KNO 3 r ]CO(NH 2 ) 2 + KCl c ]CO(NH 2 ) 2 + Nal + KI c ]CO(NH 2 ) 2 + NaNO 3 + KNO 3 r ]CO(NH 2 ) 2 + KBr r ]CO(NH 2 ) 2 + NaBr + KBr To follow up this study molar heat capacity measurements were carried out on these materials between 30 and 140 ° C using a scanning calorimeter. These molar heat capacities and enthalpies of fusion allow an evaluation of the amount of the thermal energy stored by these mixtures in the temperature range 30–140 ° C. These results have been compared with those calculated from the thermodynamic properties of the pure components. The discrepancy between the calculated and measured increases of enthalpy is particularly note-worthy for the low melting temperature eutectic mixtures and shows the necessity of experimental determinations.

Heat capacity and phase equilibria in rare earth alloy systems. R-rich R-Al alloys (R=La, Pr and Nd)

Molar heat capacities of the R-Al (R5La, Pr and Nd) R-rich alloys were determined at different temperatures by differential scanning calorimetry both by using the stepwise and the enthalpimetric methods. The results obtained for the molar heat capacity of aPr Al, 3 bPr Al and Nd Al phases have been reported together with the values obtained for liquid La-Al alloys (x 50.25). The characteristic 33 Al temperatures obtained for the different invariant reaction involved in the R-rich region have been compared with the literature data. The a∩bPr Al transformation has been confirmed at 3308C and a value of D H(10.09 kJ / mol of atoms obtained for the transformation 3 trs enthalpy.

Gallium + lead system: molar heat capacity and miscibility gap

Using a high temperature calorimeter and a differential scanning calorimeter, the molar enthalpy of formation and the molar heat capacity of the [Ga + Pb] liquid alloys have been determined. Over the entire range of composition, the heat capacity of this liquid alloy is described by the relation Cpo,ex m.liq = Cpo(liq) − [χPbCpo(Pb) + 1 − xPbCpo(Ga)] = xPb (1 − xPb)[38.76 − 0.034646T) + (6.25 + 0.00064T)(1 − 2χPb) + (−54.79 + 0.0706T)(1 − 2χPb)2] Moreover, from those measurements, the temperatures of (liq ↔ liq1 + liq2) equilibria have been obtained. Besides, the [Ga + Pb] system was assessed using a computerized optimisation procedure called Parrot of the software Thermocalc, and a set of coherent thermodynamic data. ΔmixGm,fcco and ΔmixGm,liqo have been proposed.

Enthalpie de fusion de l'urée et de quelques mélanges eutectiques à base d'urée

Abstract A research programme has been established on thermal energy storage materials for potential domestic use (T Urea was contained in a gas-tight cell and partial decomposition was observed after several heating-cooling cycles; this corresponded to the decrease in both temperature and enthalpy of fusion to constant values. tfus varied from 133 to 123°C and ΔHfus from 14.5 to 10.8 kJ mol−1. The following eutectic mixtures were investigated in the present work T001 . CO(NH2)2 + NaCl CO(NH2)2+ NaBr CO(NH22 + NAI CO(NH2)2+ KCl CO(NH2)2+ KBr CO(NH2)2+ KI CO(NH2)2+ NaNO3 CO(NH2)2+ KNO3 CO(NH2)2+ NaBr + KBr CO(NH2)2+ NaI + KI CO(NH2)2+ NaNCO3+ KNO3 The following enthalpies of fusion, in kJ mol−1, were obtained at the corresponding temperatures: T002 . 11.6 at 109.5°C 3.9 at 63.5°C 2.65 at 34°C 12.38 at 116.5 °C 12.45 at 107.5 °C 10.48 at 86.5°C 10.81 at 84.5°C 13.2 at 108.5°C 3.98 at 51°C 1.1 at 28° C 10.4 at 78.5 °C The same enthalpies were calculated from the enthalpies of phase transition and heat capacities of the pure components. The present study, together with another current study on the heat capacities of the same mixtures, will allow an evaluation of the amount of thermal energy stored by these materials in the temperature range 30–50° C.

Contribution à l'étude thermodynamique du système bismuth-gallium

Abstract The heats of mixing of liquid bismuth-gallium are measured by a high temperature Calvet calorimeter. These results, combined with those of the phase diagram, enable a complete description of the thermodynamic properties of the system.