COST 507 - Repositório Aberto da Universidade do Porto

Introduction
The project of our unit concerns the study of "Thermodynamics and phase equilibria in
the system Al-Mg-Cu-Zn-R-(Ni. Mn) with R=rare earth. Effects of rare earth additions
to Al-based or Mg-based alloys).
Within the coordination group A, work is being carried out on phase equilibria
determination and thermochemical measurements of specific rare earth containing
subsystems. On the same systems work is also in progress in the framework of
coordination group C (see the corresponding report).
In the following a summary is reported of the results obtained in the investigation of Al
and Mg alloys.
Aluminium Alloys
[96Borl] The standard molar enthalpies of formation for the different solid La-AJ and
Yb-Al alloys have been measured by means of direct calorimetry. The composition and
equilibrium state of samples were checked by micrographie and X-ray diffraction
techniques. The following values have been obtained (kJ/mol of atoms): LaAl, Af orm H°=
-46.0±2; LaAl 2 , A foral H°= -50.5.012; LaAl 3 , A form H°= -44.012; La 3 Al n , A f0rin H o =
-41.012; YbAl 2 , A f0nn H o = -39.5.012; YbAl 3 , Af oral H°= -32.5.012. Experimental results
are discussed and compared with literature data.
[96Bor2] Several applications of selected R-Al-M (R=rare earth metals, M=transition
metal) alloys for their typical characteristics such as magnetic properties have been
discussed in order to gain information on stable and metastable phases of these systems.
A systematic study on the reactivity of the R-Al and R-Al-Ni alloys has been started. To
this end calorimetrie techniques, X-ray diffraction and microscopy analyses are used. The
results so far obtained for selected Ce-Ni and Ce-Al-Ni alloy compositions have been
illustrated and discussed.
[96Bor3] The results obtained for Ce-Al-Ni system have been presented. The
thermochemical investigation was performed with an isoperibol aneroid calorimeter. The
ternary phases were synthetised directly in the calorimeter, starting from a mixture of the
finely powdered components enclosed in a gas-tigth inox crucible sealed by electric
welding. Metallographic analysis, electron probe microanalysis (ΕΡΜΑ), X-ray
diffraction analysis (powder diffraction) were used to characterised all samples, to
ascertain the absence of unreacted metals and to assess their equilibrium state. The data
so far obtained for characteristics sections have been reported, discussed and compared
with those relevant to the involved binary alloys.
[96Gam] The R-rich regions of the [Rare Earth + Al] systems (with R=La, Ce, Pr, Nd)
have been recently reinvestigated by using the differential thermal analysis techniques and
the melting behaviour of the (R+Al) alloys with a particular attention to the
thermodynamic properties has been undertaken. In this paper the first results of the
measurements of the molar heat capacity (Cp°) of some [La+Al], [Ce+Al], [Pr+AJ] and
[Nd+Al] alloys are presented and discussed.
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