Chemical and thermodynamic properties of several Al–Ni–R systems G. Borzone*, R. Raggio, S. Delsante, R. Ferro DipartimentodiChimicaeChimicaIndustriale,UniversitadiGenova,I-16146Genoa,Italy Abstract The standard enthalpies of formation at 300 K of the RNiAl phases (R=rare earth) have been obtained by using a high tem- perature direct reaction drop calorimeter and an aneroid isoperibol calorimeter. State and composition of the samples were checked by X-ray diffraction analysis. Metallographic examination was performed and the phases were further identified by electron microscopy and electron probe microanalysis. The results obtained are discussed and compared with those available for the binary RNi 2 and RAl 2 compounds. # 2003 Elsevier Ltd. All rights reserved. Keywords: A. Nickel aluminides, based on NiAl; A. rare-earth intermetallics; B. Thermodynamic and thermochemical properties; F. Calorimetry 1. Introduction The rare earth–nickel–aluminium alloys and com- pounds have received much attention due to a variety of special properties they possess. We may mention that R-Ni (R=rare earth) alloys of general composition AB 5 have been found to be prime candidates for a variety of energy applications because of their good hydrogen absorption/desorption kinetics and large hydrogen storage capacity. Substitution either of La or Ni with other elements such as an Al compo- nent was found to modify their desorption pressure [1]. The remarkable mechanical properties useful for industrial applications have been highlighted for the Al- based amorphous alloys combined with a late transition metal (M) and a rare earth (R) element. Addition of Al or Ga to R-M alloys was found to be very effective in increasing the glass-forming ability and expanding the glass formation range. Bulk amorphous alloys with diameters of several millimetres have been obtained in R-Al-M (M=Co,Ni,Cu) by the copper-casting method. Ductile (R-rich) or brittle (Al-rich) mechanical beha- viour, depending on the alloy composition, have been reported [2]. With regard to the ability of these elements to form compounds, we may observe that, generally, isothermal sections in the solid state with a rare earth content up to 30–40 at.% have been studied and data on these systems assessed [3]. As an example, Fig. 1 shows the isothermal section of the Pr–Ni–Al system at 800  C as assessed in [3]. Notice the complexity of these alloys, the high number of ternary intermediate phases present and their different stoichiometries. We may mention that the crystallochemistry of the R– Ni–Al phases is still incomplete because not all the structures have been determined and some uncertainties for several phases still remain. The objective of modern materials science is to tailor a material, starting with its chemical composition, constituent phases and microstructure, in order to obtain a desired set of properties suitable for a given application. In the investigation of complex alloy systems, sub- stantial progress could be made by an integrated approach where key experiments and thermodynamic modelling are combined in a recursive procedure. As a result, a more detailed and consistent description of the investigated systems should be obtained. The knowledge of their thermodynamic properties may therefore be useful in gaining information on stable and metastable phases. 0966-9795/$ - see front matter # 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0966-9795(03)00161-4 Intermetallics 11 (2003) 1217–1222 www.elsevier.com/locate/intermet * Corresponding author. Tel.: +39-010-353-6153; fax: +39-010- 362-5051. E-mail address: borzone@chimica.unige.it (G. Borzone).