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I.

INTRODUCTION

A

systematic description of the properties of the R-A1 (R -- rare earth metal) systems was given by Gschneidner and Calderwood. tl,2j The different binary alloys formed by Sc, Y, and all the lanthanides were described, their phase diagrams assessed, and several properties discussed. Figure l(a) shows the phase diagram of the A1-Ce system. The crystal structure data of the A1-Ce alloys are reported in Table I. A number of thermodynamic investigations of the R-Al liquid and solid alloys are reported in literature. These are summarized in Table II. As for the enthalpies of formation of solid alloys, several discrepancies appear between the values obtained by different authors with different techniques, especially for the Ce3A1 compound. A similar situation is also true for the other binary systems of aluminum with rare earths, tL2~ This can be ascribed to several experimental difficulties related to the various techniques employed and to the high reactivity and alterability of the samples, especially at high temperatures. Therefore, in the course of our systematic investigation of the thermochemistry of the rare earth alloys, E2~ it seemed useful to study the formation heats of the Ce-A1 alloys. The assessment of these values could also be useful, considering the potential technological applications of the R-AI and R-A1-Me temary alloys. Rare earth additions to Al-transition metal alloys can indeed bring about a significant modification in the microstructures, which gives rise to an improvement in strength, thermal stability, etc. t21~ The possible uses of A1-Ni-R alloys based on their capacity to absorb hydrogen have been described, t221 A review on technological properties of Al-based amorphous alloys (including R-AI and R-A1-Me alloys) has been reported by Inoue et al. t23~ Besides, Sommer and Keita I131 observed that the glass-forming ability of several R-metal alloys (especially R-AI) may be related to thermodynamic behavior of the stable phases. II.

EXPERIMENTAL

The metals used were cerium and aluminum with nominal purities of 99.9 and 99.999 wt pct, respectively. G. BORZONE, Associate Professor, G. CACCIAMANI, Researcher, and R. FERRO, Professor and Director, are with the Istituto di Chimica Generale, Universith di Genova, Genova, Italy. Manuscript submitted August 13, 1990. METALLURGICAL TRANSACTIONS A

A. Calorimetric Measurements

The formation heats were measured using the "direct calorimetry" technique. This means that the alloys are synthesized by the reaction between the components which takes place inside the calorimeter itself. It is well known 124] that this calorimetric technique is especially convenient for highly exothermic compounds formed by components which react easily. The direct calorimeter we used is an aneroid isoperibol differential instrument which has been fully described elsewhere.t25] A schematic presentation however is given here (Figure 2). The calorimeter is made up of a thick aluminum cylinder containing two small furnaces. One of these furnaces is used for sta