A. Pasturel

Enthalpies of formation of liquid and solid binary alloys of lead, antimony and bismuth with rare earth elements

Abstract The predictions of Miedemas model for the heats of formation of binary intermetallic compounds of lead, bismuth and antimony with rare earth elements and for the heats of mixing and solution of the corresponding liquid alloy systems are presented. The predicted values are compared with the existing experimental data. The differences between the experimental and the calculated values of the enthalpy are discussed.

Experimental and calculated enthalpies of formation of rare earth-tin alloys

Abstract The partial enthalpies of some rare earth elements (lanthanum, cerium, thulium, lutetium and yttrium) at infinite dilution in liquid tin were determined by means of a calorimetric method. The change in this thermodynamic property with atomic number is discussed in terms of the contribution of the 4f electrons to the bonding. This assumption is used to calculate the hybridization term involved in Miedemas relation. Experimental results therefore allow an accurate determination of the parameters of Miedemas relation. These are used to calculate the enthalpies of formation of rare earth-tin compounds. The predicted values are compared with available experimental data.

Thermodynamic study of the valence state of ytterbium in YbAl2 and YbAl3 compounds

Abstract The heats of dissolution of rare earth metals in liquid aluminium and the enthalpies of formation of YbAl 2 and YbAl 3 were measured by a calorimetric method. In the metallic state ytterbium is divalent, whereas in alloys it can become trivalent like the majority of the rare earth metals. The results of this experimental study show that the energy difference between divalent and trivalent ytterbium is 7 kcal (g atom) −1 . The enthalpies of formation of YbAl 2 and YbAl 3 are −26.1 kcal mol −1 and −31.1 kcal mol −1 respectively. The valence of ytterbium in these compounds was studied using Miedemas model.

On the heats of formation of transition metal-p metal alloys

Abstract A simple expression for the heat ΔH of formation of transition metal-p metal alloys is derived using a rigid-band model. Experimental investigations of these alloys have shown that there is an important negative heat of formation. In this work we show that this effect is due to filling of the d band of the transition metal as it is alloyed with the p metal.

Thermodynamic properties of LaNi4M compounds and their related hydrides

Abstract The enthalpies of formation of LaNi 4 Mn, LaNi 4 Cu and LaNi 4 Fe were measured by the calorimetric method. A relationship between these values and those of the enthalpies of hydrogenation is proposed. This model is applied to other systems such as LaNi 5 , LaNi 4 Al and Th(Ni 1− x Al x ) 5 .

Electronic structure and enthalpies of formation of Gd(Ni, Co, Fe)2 compounds

Abstract The electronic density of states in GdNi 2 , GdCo 2 and GdFe 2 compounds are calculated in the tight-binding d-band model by the moment method. We show a clear correlation between the position of the Fermi level in the density of states of these compounds and their enthalpies of formation which have been measured by a calorimetric method involving dissolution of the compounds in molten aluminium.

Theoretical description of phase equilibrium in the nickel-titanium system

Solid-solid and solid-liquid phase equilibrium in the Ni-Ti system is studied within the framework of the cluster variation method (CVM). The energy parameters entering the free-energy description of each phase are determined by tight-binding energy calculations using the cluster Bethe lattice method (CBLM). For simplicity, the pair interactions are restricted to first-nearest neighbours in FCC-based structures and to first- and second-nearest neighbours in BCC-based structures. The configurational entropy for disordered solutions and for ordered compounds are obtained using the tetrahedron approximation of the CVM. The three compounds NiTi, Ni3Ti and NiTi2 compounds are treated as stoichiometric compounds. The calculated diagram agrees reasonably well with that determined experimentally.

A statistical approach to the structure of the hydrides of haucke compounds

Abstract Two structures have recently been proposed for β-LaNi5 hydride. A statistical thermodynamic description leads to self-consistent relations between the thermodynamics and the occupation of interstitial sites by the hydrogen atoms; in the case of the P6/mmm group the reduction in the number of available interstitial sites brought about by the occupation of other interstitial sites is taken into account. The calculated configurational entropies for both structures are identical, but the calculation of the enthalpy change shows that the hydrogen absorption is more favourable in the structure with space group P6/mmm.

Determination of the partial enthalpies of trivalent rare earth or transition metals in liquid aluminium or silicon

Abstract A method of calculating the partial enthalpies of transition metals or trivalent rare earth metals in aluminium or silicon is proposed. In both cases it is assumed that the interactions between the impurity and the host lead to the filling of the d band of the transition or rare earth metal by electronic rearrangement. The calculation is applied to T-Si alloys (TFe, Co, Ni) and to trivalent rare earth metal-aluminium systems. The calculated results are compared with experimental data and demonstrate the important role of volume effects.

Molecular dynamics of topological and chemical orders in liquid Al1-xMnx alloys

We present an atomistic simulation of the structure of liquid Al1-xMnx alloys based on interatomic forces derived from quantum theory. Using the intra-atomic potentials calculated within the tight-binding bond approach, we study the structural properties of liquid Al80Mn20 and Al60Mn40 alloys using molecular dynamics simulations. The results are in good agreement with the most accurate diffraction data. The correlation of the structural trend with the characteristic variation in the electronic structure is established.