Jean Pierre Bros

High-temperature calorimetry in metallurgy

Abstract This paper presents an overview of calorimetric methods for obtaining enthalpies of formation of n -component liquid or solid alloys in the temperature range 500–1800 K. Emphasis is given to: the recent developments of techniques which have enlarged the field of calorimetry in the thermochemistry of alloys, molten salt and oxide mixtures; the specific difficulties encountered in the high-temperature range; and the strengths and weaknesses of the selected solutions.

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.

Experimental and Calculated Ag + Au + Ge Phase Diagram

The investigation of the equilibrium phase diagram of the Ag + Au + Ge system has been carried out by the following ways: (a) the location of equilibrium surfaces was determined on the whole composition range by high temperature isoperibolic calorimetry and differential thermal analysis; (b) the equilibrium temperatures of the ternary system were calculated from the equilibrium temperatures and the thermodynamic functions referring to the three limiting binary alloys Ag + Au, Ag + Ge, Au + Ge. A satisfactory agreement was found between the calculated liquidus and the one obtained by calorimetry and thermal analysis. In the course of a systematic thermodynamic investigation of ternary alloys based on gold, silver, and a IV b metal, the three systems Ag + Au + Si, Ag + Au + Ge, and Ag + Au + Sn were examined; the molar enthalpies of formation of the liquid mixtures were obtained on the one hand and the equilibrium phase diagrams on the other.1,2,3 This paper focuses on the latter topics for the ternary alloys Ag + Au + Ge; a comparison is carried out between the equilibrium temperatures measured by differential thermal analysis at the laboratory S.E.T.T. in Marseille and those calculated at the Royal Institute of Technology in Stockholm. This calculation is based on the thermodynamic data published for the limiting binary systems and also on the ternary enthalpies measured by calorimetry at very high temperature.

Thermodynamics of nickel-tin liquid alloys

Copyright (c) 1996 Elsevier Science B.V. All rights reserved. An automated very high temperature calorimeter has been used to investigate the partial and integral enthalpies of mixing of liquid nickel+tin alloys in the temperature and molar fraction range 867<T/K<1579 and 0<x Ni <0.80 respectively. The enthalpies of mixing, D mix H° m =f(x Ni r are exothermic over the entire concentration range. They are represented by the following equation for temperatures between 1530 and 1580K: D mix H° m /kJmol −1 =x(1−xr(−46.01−6.788x−209.616x 2 +203.879x 3 −20.145x 4 r where x=x Ni . The coordinates of the minimum are D mix H° m =−20.2p0.6kJmol −1 at x Ni =0.60. The limiting partial molar enthalpy of Ni in liquid tin, referred to liquid Ni, was determined to be h° m (Ni (l& rpar; in ∞ Sn (l& rpar;r/kJmol −1 =−36.48−12960/T over the entire temperature range scanned. The change in Fermi enthalpy on alloying indicates a restricted number of electrons transferred from Sn to Ni for alloys with x Sn ?0.75. Higher tin concentrations do not change the number of electrons accepted by Ni.

Enthalpies of formation of the Ag- Au- Si, Ag- Au- Ge, and Ag- Au- Sn Ternary Liquid Alloys; experimental determinations and application of the hoch- arpshofen model

The enthalpies of formation of the Ag-Au-Si, Ag-Au-Ge, and Ag-Au-Sn ternary liquid alloys were measured by very high-temperature calorimetry. Measurements were carried out between 1373 and 1550 K and enthalpies were obtained with an accuracy of 8 pct. Then the same ternary enthalpies of formation were calculated using the Hoch-Arpshofen model, and a comparison between experi-mental and calculated values was performed on the whole composition range.

Thermodynamic investigation of the LuPb system

The LuPb alloys were studied by different techniques. The molar heat capacities of the solid compounds Lu5Pb3 and Lu6Pb5 were determined in the range 525–823 K using differential scanning calorimetry. The enthalpy of formation of LuPb2 was obtained by both emf and calorimetric methods. Potentiometric measurements were performed in the range 610–730 K and a value of −35 ± 2 kJ (mol at.)−1 was obtained for the enthalpy of formation of LuPb2 in the solid state at 298 K. By using a direct isoperibolic aneroid differential calorimeter the value ΔformH = −34 ± 2 kJ (mol at.)−1 was determined. The data obtained in this study are compared with those of other similar rare earth-lead compounds and discussed briefly.

The PdPb system: excess functions of formation and liquidus line in the range O <XPd < 0.60 and 600 <T < 1200 K

Using a galvanic cell with liquid electrolyte, the activity of lead in the PdPb system has been investigated in the molar fraction range 0.10 <XPd < 0.60 between 600 and 1200 K. With a second technique, high temperature calorimetry, the molar enthalpy of mixing has been measured at 952, 1108 and 1170 K and the coordinates of the extremum of ΔmixHom=f(xPd) have been found (ΔmixHom= −38±2 kJ mol−1 with xPd=0.66). From these experiments, on one hand, the molar partial free energies, entropies and enthalpies of lead were obtained and, on the other hand, the molar integral enthalpy was calculated and the limiting molar partial enthalpies of liquid palladium (ΔHom(Pd(liq.) in ∞ liquid Pb)=−78±3 kJ mol−1) and liquid lead (ΔHom(Pb(liq.) in ∞ liquid Pd) = −272± 10 kJ mol−1) were extrapolated. Similarly to the liquid PdGa and PdIn systems, the enthalpy of formation of the PdPb alloy is exothermic and the ΔmixHom=f(xPd) curve is asymmetrical. These data indicate strong interatomic bonds in the liquid state. Moreover, the coordinates of several (liq.↔ liq. + PbxPd1−x(sol.)) equilibrium points (liquidus points) have been deduced in this concentration range.