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Thermodynamic properties and phase equilibria in alloys of the Al—Ce system

N.Podopryhora 1,
 
M.S.Kobylinska 2,
 
V.G. Kudin 2,
 
L.Romanova 1,
 
V.Sudavtsova 1*
 

1 I. M. Frantsevich Institute for Problems of Materials Science of the NAS of Ukraine, Kyiv
2 Taras Shevchenko National University of Kyiv, Kyiv
sud.materials@ukr.net

Usp. materialozn. 2024, 8/9:112-126
https://doi.org/10.15407/materials2024.08-09.011

Abstract

The thermochemical properties of melts of the Al—Ce system at temperatures of (1380— 1490) ± 3 K in range of compositions 0 < xAl < 0,38 were determined by the method of isoperibolic calorimetry. It was established that the minimum value of the enthalpy of mixing of these melts is −40,9 ± 4.1 kJ/mol and corresponds to the melt with xAl = 0,67, and =−83,3 ± 4,8; = −200 ± 26,0 kJ/mol. Using our own and literature thermochemical data for melts and intermediate phases of the Al—Ce system, as well as its diagram state according to the ideal associated solution (IAS) model, all thermodynamic properties of melts and associates in melts and intermetallics were calculated and optimized. It was established that the calculated activities of the components in the melts of this system show large negative deviations from ideal solutions. which correlates with their thermochemical properties. The maximum mole fraction of associates CeAl2, CeAl reaches values of 0,4 and 0,24, and the other three (Ce2Al, CeAl3, CeAl5) — 0,16; 0,08, and 0,11, respectively. The minimum values of Gibbs energies and entropies of melt formation are equal to -28,2 kJ/mol and -7,6 J/mol·K. The temperature-concentration dependences of Gibbs energies, enthalpies and entropies of melt formation and temperature for intermetallics were also calculated using the IAS model, and from them, the liquidus curve of the phase diagram of this system. As a result, complete information on the thermodynamic properties of all phases and the liquidus curve of the phase diagram of the Al—Ce system was obtained. In order to confirm the reliability of the obtained data and search for general regularities of the thermodynamic characteristics of alloying of the Al—Ce system, it was considered as a member of the series of Al—Ln(Ln-lanthanide) systems. For this, the enthalpies of formation were analyzed. intermetallics LnAl2, as well as the minimum values of thermochemical properties of melts, relative differences in molar radii and differences in electronegativities of the components of the Al—Ln systems and their dependence on the lanthanide serial number. It is shown that all dependences, except for the electronegativity differences of the components, are compatible with each other. This indicates that the thermodynamic properties of compounds and melts of Al—Ln systems are determined by the size factor.

 


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ACTIVITIES, ALUMINUM, CALORIMETRY, CERIUM, ENTHALPIES OF MIXING, INTERMETALLID, MELTS, MODEL OF IDEAL ASSOCIATED SOLUTIONS, PHASE EQUILIBRIA, THERMODYNAMIC PROPERTIES

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