N. Selhaoui

Standard enthalpies of formation of scandium alloys, Sc+Me (MeFe, Co, Ni, Ru, Rh, Pd, Ir, Pt), by high-temperature calorimetry

Abstract The standard enthalpies of formation of scandium alloys, Sc+Me (MeFe, Co, Ni, Ru, Rh, Pd, Ir, Pt) were determined by direct synthesis calorimetry at 1473±2 K . The following values of Δ f H m o /(kJ g atom −1 ) are reported: Fe 2 Sc, −(11.2 ± 1.2); Co 2 Sc, −(32.5 ± 2.1); CoSc 2 , −(26.7 ± 1.9); Ni 2 Sc, −(43.0 ± 2.3); NiSc, −(44.7 ± 2.3); RuSc, −(44.5 ± 2.2); Rh 3 Sc, −(51.7 ± 1.4); RhSc, −(94.5 ± 1.5); PdSc, −(89.3 ± 2.2); IrSc, −(89.7 ± 3.0); Ir 2 Sc, −(66.3 ± 1.3); PtSc, −(104.8 ± 5.4). The results are compared with predicted values, and with earlier data for some of the corresponding yttrium and titanium alloys.

Standard enthalpies of formation of lanthanum alloys, La + Me (MeRu, Rh, Pd, Os, Ir, Pt), by high-temperature calorimetry

Abstract The standard enthalpies of formation of lanthanum alloys, La+Me (MeRu, Rh, Pd, Os, Ir, Pt) were determined by direct synthesis calorimetry at 1473 ± 2 K. The following values of Δ f H m 0 (in kJ g −1 atom −1 ) are reported: LaRu 2 −(10.3 ± 2.8); LaRh 2 (57.5 ± 1.7); LaRh −(56.3 ± 2.3); LaPd −(76.2 ± 1.8); LaPd 3 (−77.1 ± 2.2); LaOs 2 −(9.0 ± 1.1); LaIr 2 −(62.9 ± 2.2); LaIr 3 (−49.7 ± 2.2); LaPt 2 −(90.0 ± 2.9); LaPt 3 −(92.1 ± 4.6). The results are compared with predicted values from the models of Miedema et al. , of Watson and Bennett, and of Colinet and Pasturel , and with earlier data for some of the corresponding yttrium and scandium alloys.

Enthalpies of formation of some solid hafnium nickel compounds and of the Ni-Rich HfNi liquid by direct reaction calorimetry

In the course of a systematic study of binary transition metal alloys, the enthalpies of formation of five Hf-Ni compounds were measured by direct reaction calorimetry: Hf0.17Ni0.83(l/6HfNi5): ΔfH(1323 K) = − 37,000 J/mole of atoms (±3200) Hf0.22Ni0.781/9Hf2Ni7): Δf(1623 K) = −50,700 J/mole of atoms (±2000) Hf0.45Ni0.55(l/2OHf9Ni11): ΔfH(1473 K) = −54,500 J/mole of atoms (±2200) Hf0.50Ni0.50(l/2HfNi): ΔfH(1573 K) = −47,900 J/mole of atoms (±1800) Hf0.67Ni0.33(l/3Hf2Ni): ΔH(1423 K) = −36,700 J/mole of atoms (±1300) with reference to pure metals in their equilibrium states at the reaction temperatures. The Ni-rich Hf-Ni liquid was also studied by the dissolution of Hf in the liquid alloy of variable composition at 1743 and 1633 K. Results show that the enthalpy of formation of the liquid at a given composition depends strongly on temperature, and this point suggests the existence of associations in the liquid. The melting temperature of Hf0.22Ni0.78(Hf2Ni7) which was found (1705 K) is slightly lower than the one (1743 K) given in the literature.

Thermodynamic study of the Pd-Hf system by high-temperature calorimetry

Abstract The enthalpies of formation of five Hf-Pd compounds were determined by direct synthesis calorimetry. The values of ΔfH are reported for HfxPd(1−x) (x = 0.67, 0.50, 0.43, 0.33 and 0.25) with reference to pure metals in their equilibrium states at the reaction temperatures. The results are compared with some earlier experimental data and with predicted values from published models.

Thermodynamic description of the Lu–Pb binary system

The thermodynamic modeling of the Lu–Pb binary system was carried out with the help of CALPHAD (Calculation of PHAse Diagram) method. The liquid phase has been described with the association solution model with “Lu5Pb3” as an associated complex. Lu5Pb3, α-Lu5Pb4, β-Lu5Pb4, Lu6Pb5, and LuPb2 have been treated as stoichiometric compounds, while a sublattice model has been used for the description of the HCP phase. The calculations based on the thermodynamic modeling are in good agreement with the phase diagram data and experimental thermodynamic values.

Thermodynamic assessment of the Ytterbium–Germanium binary system

The Ytterbium–Germanium binary system was evaluated using the CALPHAD method through Thermo-Calc software package; the thermodynamic parameters involved in the Gibbs free energy models of the phases are optimized based on all available literature experimental data including the phase equilibria information and few thermodynamic measurements. The Ytterbium–Germanium system contain six intermetallic compounds Yb2Ge, Yb5Ge3, Yb5Ge4, Yb11Ge10, Yb3Ge5, and Yb3Ge8, which are all treated as stoichiometric phases. The excess term of the Gibbs free energy of the liquid phase was assessed with the recent exponential temperature dependence of the interaction energies by Kaptay and compared with the linear temperature dependence of Redlich–Kister polynomial equation results. The Germanium (Diamond_A4) and the two allotropic transformations of Ytterbium: βYb (fcc_A1) and γYb (bcc_A2), were kept as pure element phases since no solubility of Germanium in Ytterbium and vice versa. A reasonable agreement between the calculated results (the phase diagram and model parameters) and literature data was obtained for this system. The optimization process allows us to accomplish the results which are reported in a series of figures and tables.

Thermodynamic modeling of the thulium–germanium binary system

The thulium–germanium binary system has been critically assessed by means of the CALculation of PHAse Diagram technique through Thermo-Calc software package. The thulium–germanium binary system contains nine phases based on eight compounds, the intermediate phases with no solubility ranges: Tm5Ge3, Tm5Ge4, Tm11Ge10, TmGe, Tm4Ge5, TmGe1.5, and Tm0.9Ge2 were treated as stoichiometric phases, while the compound with homogeneity range TmGe1.8 (TmGe1.8_LT and TmGe1.8_HT) was modeled using two sublattices model as (Ge,Tm)0.358(Ge)0.642. The liquid phase was modeled as substitutional solution phase, in which the excess Gibbs free energy was formulated with Redlich–Kister polynomial. The germanium (diamond_A4) and thulium (hcp_A3) were kept as pure element phases since no solubility of germanium in thulium and vice versa. The calculations based on the thermodynamic modeling agree well with the phase diagram data and few experimental thermodynamic values from the literature.

Eutectic Morphology in Alloy Pb – 3.2% Cd – 0.08% Sr for Battery Grids

Ageing of supersaturated solid solution in Pb – 3.2% Cd – 0.08% Sr alloy is studied at 20 and 80°C by measuring hardness, and light and scanning electron microscopy. Structural changes are established corresponding to stages of ageing and supersaturation.

Modélisation numérique du systeme La-Ru

Abstract The present study concerns the optimization of the La-Ru system by the use of the NancyUn software, taking into account the available experimental results about phase equilibria and thermodynamic properties. The computer program allows us to obtain estimated data for experimentally undetermined thermodynamic properties and to compare the computed phase diagram with the one already published.

Optimization of the binary Ce–Ru system

Abstract The present study concerns the optimization of the Ce–Ru system with the help of NANCYUN software and experimental results about phase equilibria and thermodynamic properties. The computer program allows us to obtain estimated data for thermodynamic properties which have not been determined by experience and to check the consistency of what is available in literature.