Olena A. Bieloborodova

THERMODYNAMIC PROPERTIES OF LIQUID Al-Si AND Al-Cu ALLOYS

The partial and integral enthalpies of mixing in liquid Al-Si and Al-Cu alloys were determined by high-temperature isoperibolic calorimetry at 1750±5 and 1590±5, respectively. The thermodynamic properties of Al-Si melts were also studied by electromotive force method in temperature range 950-1270 K. The partial and integral excess Gibbs free energies of mixing in liquid Al-Si and Al-Cu alloys were also calculated from literature data on thermodynamic activity of aluminium. The comparison of our experimental results with literature data has been performed.

Thermodynamics of liquid Fe-Si and Fe-Ge alloys

The enthalpies of mixing of liquid binary Fe-Ge (1765±5 K) and Fe-Si (1750±5 K) alloys were determined using a high-temperature isoperibolic calorimeter. The thermodynamic properties of Fe-Ge melts were also studied by electromotive force method in the temperature range of 1250-1580 K. The comparison of our measurement results with literature data has been performed. The extreme negative values of integral enthalpy of mixing and alternating-sign deviations from Raoults low for germanium can be explained by the influence of binary clusters formation.

Thermodynamics of liquid aluminium-copper-germanium alloys

Abstract Partial for aluminium and integral enthalpies of mixing of liquid Al–Cu–Ge alloys have been measured by high-temperature isoperibolic calorimetry at T=(1380±5) K. Thermodynamic activities, partial for aluminium and integral Gibbs free energies of mixing have been determined by the electromotive force method (emf) over the range 1050⩽T/K⩽1250. Integral excess entropies of mixing have been calculated from calorimetric enthalpies and emf measured Gibbs free energies of mixing. The integral enthalpies of mixing and the integral excess Gibbs free energies of mixing have been also evaluated based on the literature data for boundaries using the Bonnier geometric model. Differences between experimental and calculated thermodynamic functions of mixing are positive. These facts as well as negative excess integral entropies of mixing reveal information about microsegregation in the melt. Therefore, the existence of ternary eutectic has been forecasted for Al–Cu–Ge phase diagram.

Enthalpies of mixing of liquid Al - Fe - Ge alloys

Abstract The partial and integral enthalpies of mixing of Al–Fe–Ge melts have been measured by high-temperature calorimetry at 1740 ± 5 K. The integral enthalpies of mixing at 1173 K, are about 4 to 6 kJ mol–1 less negative than determined by electromotive force measurement [9]. The integral enthalpies of mixing have been also estimated on the basis of the Bonnier geometric model. The calculated values show a reasonable agreement with experimental data for xGe > 0.3. A difference between experimental and estimated integral enthalpies of mixing (up to 2.5 kJ mol–1) is observed for ternary alloys with low germanium content.

High-temperature Calorimetry of Liquid Gd-Si and Y-Si Alloys

Molten Gd-Si and Y-Si alloys were examined calorimetrically at 1760 and 1770 K, respectively. The partial enthalpies of mixing of gadolinium (Δmix H̅Gd), yttrium (Δmix H̅Y) and silicon (Δmix H̅Si) were measured. The integral enthalpy of mixing (ΔmixH) was calculated by Darken’s method. The available thermodynamic data of liquid (Gd,Y)-Si alloys were compared. The partial enthalpies of mixing of Gd and Y, and appropriate integral enthalpies of mixing, were described by polynomial dependencies versus mole fraction of Gd or Y.

EMF study of liquid Al - Fe - Ge alloys

The thermodynamic properties of ternary liquid Al - Fe - Ge alloys have been studied in the temperature range of 1050 - 1250 K by the electromotive force (EMF) technique with a liquid electrolyte. The ternary alloys are character- ized by negative deviations from Raoults law. dium chloride (purity 99.5 %) and aluminium chloride (pur- ity 99.95 %) were purchased from Sigma-Aldrich and were used for the electrolyte preparation. The electromotive forces of ( - )Ta|Alliq| AlCl3 in KCl + NaCl (azeotropic solution) |(AlxFeyGe 1- x - y)liq| Ta(+) concentration cells were measured in the temperature range of 1050 - 1250 K under argon at atmospheric pressure. The EMF values at one temperature were measured several times both during heating and during cooling of the melt. The thermodynamic properties of liquid ternary alloys were studied for four cross-sections with xGe : xFe being 0.55 : 0.45, 0.6 : 0.4, 0.7 : 0.3, and 0.85 : 0.15. The Al mole fraction was from 0.1 up to 0.8. The cell construction, rou- tine of electrochemical technique, and mathematical pro- cessing of the initial experimental data are described in (4). The partial thermodynamic functions of mixing of Al were calculated from the EMF data for the temperature of 1173 K. The integral excess thermodynamic functions of mixing were defined from the partial ones by integration of the Gibbs-Duhem equation: