N. Parodi

Thermodynamic measurements and assessment of the Al–Sc system

Abstract A study of the binary Al-Sc phase diagram has been performed by means of thermodynamic calculations and experimental measurements. The enthalpy of formation of all intermetallic compounds has been determined and a cursory examination of the phase equilibria carried out, for compositions greater than 40 at% Sc. Two new invariant reactions have been identified in the Sc-rich part of the diagram: L ↔ (βSc)+Sc2Al at 1185°C and (βSc) ↔ Sc2Al+(αSc) at 970°C. A coherent set of Gibbs energy expressions for all the phases in the system has been generated by a least square optimisation procedure using all the experimental data available. The overall agreement is satisfactory but some uncertainties still persist, especially concerning the ScAl phase, owing to experimental difficulties.

Aluminium compounds of the rare earths: enthalpies of formation of YbAl and LaAl alloys

Abstract The standard molar enthalpies of formation for the different solid LaAl and YbAl alloys have been measured by means of direct calorimetrr. The composition and equilibrium state of the samples were checcked by micrographic and X-ray diffraction techniques. The following values have been obtained 1kJ (mol atoms)1): LaAl, ΔformH° = −46±2; LaAl2 ΔformH° = −50.5±2; LaAl3 ΔformH° = −44.0±2; La3Al11 ΔformH° = −41.0±2; Ybal2 ΔformH° = −39.5±2; YbAl2 Δform H° = −32.5±2. Experimental results are discussed and compared with literature data.

On the thermochemistry of the rare earth compounds with thep-block elements

A summary is given of the experimental work carried out to determine the heats of formation of the rare earth compounds with a number of elements of thep-block of the periodic table (in particular Al, In, Sn, Pb, As, Sb, and Bi). The experimental methods and the devices constructed to this end are briefly described and commented on. Some results recently obtained in the thermochemical investigation of binary (Pr-Al and Gd-Pb) and ternary (Ce-Ni-Al and La-Sb-Bi) alloys are presented.

Comments on the formation thermodynamics of selected groups of rare earth compounds

In the framework of a description of the general alloying behaviour of the rare earth (R) metals, their reaction thermochemistry is reviewed. Problems met in the thermochemical characterization and in the experimental investigation of R alloys and compounds are highlighted and discussed. A short summary of the work in this field, carried out in our laboratory is reported. Special attention is given to the work performed and in progress on selected groups of R compounds: these are aurides, arsenides, antimonides, bismuthides and tellurides. The results obtained in the standard enthalpy measurements by direct calorimetry for RAu compounds, La-As, Tb-Bi and 0 Ce-Te solid alloys are reported and discussed. Typical values of D H (kJ / mol at. at 300 K) are: LaAu, 272.062.0; Ce Au, f 2 255.061.0; GdAu, 282.062.0; TbAu, 282.062.0; DyAu, 282.063.0; HoAu, 283.064.0; YbAu, 275.062.0, LaAs, 2150.063.0, TbBi, 2104.062.0; CeTe, 216864 and Ce Te -Ce Te , 216364.

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.

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.

Contribution to the thermochemistry of rare earth pnictides: the Sm-Bi system

Formation enthalpies of Sm-Bi alloys (in the complete range of compositions) and Er-Bi alloys (for a few compositions) have been measured using a direct, small-furnace, isoperibolic aneroid differential calorimeter. Typical values for the reaction in the solid state at 300 K are: Sm2Bi,−88 ± 3; Sm5Bi3, −94 ± 4; Sm4Bi3, −104 ± 2; SmBi, −108 ± 2; SmBi2, −76 ± 4; and ErBi, −90 ± 5 kJ/g-atom.The experimental data are briefly discussed, compared with those of similar rare earth compounds, and found to be in good agreement with those computed according to the Miedema model and, for the rare earth-rich alloys, also with those calculated according to the Kubaschewski suggestion based on the so-called “effective coordination number” in alloys.

Calorimetric determination of the enthalpies of formation of liquid and solid YbPb alloys

Abstract The enthalpies of formation of liquid and solid YbPb alloys have been determined by using high-temperature calorimetry and direct calorimetry, respectively. The enthalpies of mixing of liquid YbPb alloys have been measured in the temperature range 960–1100K and the results are discussed on the basis of the association model. Formation and melting enthalpies have been measured for the intermetallic compounds Yb2Pb, Yb5Pb3, YbPb and YbPb3. The formation enthalpies of the solid phases are in agreement with the presence in the alloys of divalent Yb. Typically for the formation, in the solid state at 300K, of Yb2Pb the following values were obtained: −66.0 ± 5 kJ (mol at.)−1 by solution calorimetry and −67.0 ± 3 kJ (mol at.)−1 by direct calorimetry.

Gd–Sb system: standard enthalpies of formation of solid alloys and crystal structure of Gd16Sb39

Abstract The data obtained in the investigation of Gd–Sb alloys are reported. This investigation was performed using metallographic and X-ray diffraction analyses and calorimetric measurements of the enthalpies of formation at 300 K. The values of ΔfH° (kJ/mol of atoms ±2) for the following compounds were obtained for the reaction in the solid state at 300 K: Gd5Sb3: −110; Gd4Sb3: −116; GdSb: −120; Gd16Sb39: −78. The crystal structures of Gd5Sb3 (hP16-Mn5Si3 type), Gd4Sb3 (cI28-anti-Th3P4 type) and GdSb (cF8-NaCl type) have been confirmed. The crystal structure of the compound previously called “GdSb2” was determined by single-crystal methods and the composition Gd16Sb39 was found.

Thermodynamic investigation of samarium–nickel alloys

Abstract The enthalpies of formation of the Sm–Ni solid alloys at 300 K were determined by direct calorimetry using two different calorimetric apparatus. The characterization of the samples was performed using metallographic and X-ray diffraction analyses. The values of Δ f H ° (kJ/mol of atoms) for the following compounds were obtained for the formation in the solid state at 300 K: Sm 3 Ni: −21.5±2; SmNi: −33.0±1; SmNi 2 : −36.0±1. The results are discussed and compared with those of other similar rare earth–nickel compounds.