COST 507 - Repositório Aberto da Universidade do Porto

calculate the thermodynamic mixing functions of the ternary alloys based on the
thermodynamic properties of the binary bordering systems. The calculated values of
the enthalpy of mixing show a good agreement with measured values within the range
of experimental accuracy. The presence of additional ternary interactions or ternary
associates in the liquid state could not be observed.
Enthalpies of mixing of ternary liquid Cu-Mg-Y alloys were determined along five
different sections. For one of these sections (XGAY = 0.5), magnesium vapor pressures
were measured by means of an isopiestic method (A2), and the corresponding values
of the magnesium activity at 1173 K were derived as a function of composition. The
Gibbs energy of mixing was computed by a Gibbs-Duhem integration. An association
model was applied to calculate the thermodynamic functions of mixing for ternary
liquid alloys using the model parameters of the base binary systems.
Thermodynamic properties of ternary liquid Cu-Mg-Si alloys with a constant
composition ratio xci/xs¡ = 7/3 were determined using a combination of different
experimental methods: Enthalpies of mixing were measured by isoperibolic
calorimetry and magnesium vapor pressures were obtained by an isopiestic method
(A2). Partial thermodynamic properties of magnesium were derived from the vapor
pressure data, and the composition dependence of the magnesium activities is given for
1173 K. Gibbs energies of mixing for liquid alloys were calculated by a Gibbs-Duhem
integration. Finally, an association model was applied to provide the thermodynamic
functions of mixing for ternary liquid alloys using the model parameters of the three
limiting binary systems.
The enthalpy of mixing of liquid Al-Cu-Zr alloys were determined along eigth
different sections at 1480 ± 5 K using two different measurement procedures. The
enthalpy of mixing exhibit very negative values with a rninimum of about -53 kJ mol" 1
at the composition Al5 0 Cu 2 oZr3o.
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