J. Hertz

The enthalphy of mixing of the intermediate phases in the systems FeTi, CoTi, and NiTi by direct reaction calorimetry

The enthalphy of mixing of some intermediate phases in the systems FeTi, CoTi, and NiTi have been measured by direct reaction calorimetry between 1200 and 1500 K. The method is described, the results are given and compared with available data from diagram estimations and from earlier experimental work.

New aspect of the solid phase equilibria in the ternary PbSnCa system for xCa≤25 at.%

Abstract New crystallographic data prove that CaPb 3 and Sn 3 CaL1 2 compounds belong to the same single-phase Ca(Pb,Sn) 3 domain in the ternary PbSnCa equilibrium phase diagram. A tentative calculation of this diagram shows that about 2 wt.% Sn, introduced in the α-Pb matrix, allows a decrease in the solubility of Ca at 400 K from 10 t-2 to 10 −7 wt.%. Simultaneously, the L1 2 compound, in equilibrium with the α-Pb matrix, crosses rapidly the x Ca =0.25 line, continuously from the PbCa border to near the SnCa border, when increasing the Sn content in the α matrix from zero to 8 wt% Sn at 400 K. A very large triangle formed by the three phases α-Pb (8 wt% Sn), β-Sn (1.7 wt.% Pb), Ca 25 Pb 5 Sn 70 L1 2 appears in this diagram at 400 K. This triangle provides a ternary eutectic, calculated at 424 K. This calculation brings to light some reasons for the process transition for the hardening of PbCa grid-battery alloys, from discontinuous to continuous, when increasing the tin content.

Enthalpic and structural studies of the NiZr system

Abstract The enthalpies of formation of four phases in the NiZr system were studied by direct reaction calorimetry at high temperatures. The results for the phases Ni0.33Zr0.67, Ni0.50Zr0.50, Ni0.78Zr0.22 and Ni0.83Zr0.17 are given, discussed and compared with the calculations of Miedema and Niessen and of Watson and Bennett. The phase structures were analysed by X-ray diffraction techniques.

Determination electrochimique, par pile a electrolyte solide CaF2, des proprietes thermodynamiques de formation des alliages binaires (Ca, Cu) entre 800 et 1300 K

Abstract Thermodynamic quantities of formation of the CaCu system intermetallic phases are, for the first time, directly determined by means of electromotive force measurements. The alloy sample is prepared, in situ, on a copper point electrode by electrolysis. The activity of calcium in CaCu alloys is directly compared with that of pure calcium (liquid or solid) produced in the same conditions on an inert (iron) electrode.

The enthalpies of formation of the intermediate phases Co0.33Zr0.67,Co0.50Zr0.50, Co0.67Zr0.33 and Co0.80Zr0.20 by direct reaction calorimetry at high temperature

Abstract The enthalpies of formation of four solid phases of the CoZr system were measured by direct reaction calorimetry at temperatures in the neighbourhood of the phase melting points. The products were checked by X-ray diffraction and microprobe analysis. The results are described and compared with numerical data reported recently.

The Gibbs energy and entropy of formation of intermetallic Al-Ca compounds: Solid electrolyte galvanic cell studies

Abstract The Al-Ca alloys were made in situ in an (Ni, NiO)¦CaF2¦(Al, Ca) cell by reducing CaF2 in contact with an aluminium pinpoint electrode. The depolarization curve showed the successive appearance of intermediate phases of the Al-Ca system in contact with the aluminium electrode. The activity of calcium in the compound was compared with that of pure calcium. In this way the Gibbs energies and entropies of formation of Al4Ca and Al2Ca were determined in the range 750–900 K: ΔfG(Al0.8Ca0.2, 800 K) = −17 800 ± 140 J mol−1ΔfG(Al0.67Ca0.33, 800 K) = −28 500 ± 300 J mol−1ΔfS(Al0.8Ca0.2, 800 K) = −1.1 ± 0.5 J K−1 mol−1ΔfS(Al0.67Ca0.33, 800 K) = −6.1 ± 1.1 J K−1 mol−1

Piles de mesure àélectrolyte solide utilisant une ou deux électrodes ponctuelles en régime transitoire: I. Application à la mesure des enthalpies libres standards d'oxydation des métaux purs

The point electrode is a metal point touching a solid electrolyte (calcia stabilized zirconia), in an atmosphere with a controlled oxygen partial pressure. The system is equipped with an oxygen pump mounted before the cell, which is electronically controlled and attains 10−20 atm O2. The potential-time curves of the depolarisation of the point electrode permits a dynamic study of the oxidation of the metal, or of the reduction of its oxide. The point electrode has a very small inertia; the steps on the potential-time curves, even when strongly inclined, can be used to determine the standard free enthalpies of oxidation of pure metals. The measuring cell can be equipped, either with one point electrode associated with a reference electrode at a stable potential, or with two point electrodes placed side by side without any separation. The results obtained for the systems CuCu2O and CoCoO serve as applications.

Determination calorimetrique de l'enthalpie de formation des alliages (Al, Ba) riches en aluminum

Abstract The heats of formation of some aluminium-barium alloys have been determined by drop calorimetry at high temperature. The heats of mixing of pure liquid Al and Ba to give the liquid alloy are Δ m H ( x Ba =O.056, 1215 K)=−6.6 kJ mole −1 and Δ m H ( x Ba =O.333, 1215 K)=−31.0 kJ mole -1 . To measure its heat of formation, the solid compound Al 4 Ba was precipitated by addition of pure barium from a liquid (Al, Ba) bath. It was found that Δ f H (Al 0.8 Ba O.2 , solid, 1215 K)=-(37.1 ∓ 1.5) kJ mole −1 with reference to the pure metals in the solid state.

Etude par effusiometrie de torsion des proprietes thermodynamiques en phase solide des laitons binaries (Cu, Zn)

Abstract The Gibbs thermodynamic variables which we have determined for thirteen brass alloys (Cu, Zn) are in good accord with the literature. The experimental conditions were as close as possible to those of sublimation in static vacuum. The application of the test of the third law in β-brass shows that our free enthalphy measurements are in agreement with the measurements of specific heat by Moser. The primary solid solution α copper of the binary brasses shows quasi-regular behaviour over the whole composition range. Our measurements seem to indicate the existence of a β′/(α + γ) eutectoid at a temperature less than 100°C. The high degree of order of the γ phase is seen in the large negative values of excess entropy.

Experimental diagram and numerical optimization of the CaNi system

Abstract The nickel-rich part of the Ca-Ni system has been studied by differential thermal analysis at high temperature. The CaNi 5 compound melts congruently at 1484 ± 5 K ; the eutectic arrest between nickel and CaNi 5 was measured at 1451 ± 5 K ; the peritectic melting of Ca 2 Ni 7 was observed at 1401 ± 5 K . All the well-known values of thermodynamic functions, together with diagram data, were used in a numerical optimization of the phase diagram, using a Legendre polynomial development (NANCYUN program) of the Gibbs excess function of the liquid phase. A complete set of recalculated values for the phase diagram and the thermodynamic functions is proposed.