Thermodynamic analysis of aluminate formation at Fe/Al2O3 and Cu/Al2O3 interfaces

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Abstract

Subsolidus ternary phase relationships in the systems Fesingle bondAlsingle bondO and Cusingle bondAlsingle bondO are reviewed in order to provide a basis for thermodynamic analysis of aluminate formation at Fe/α-Al2O3 and Cu/α-Al2O3 interfaces. Expressions for the critical oxygen activity in the Fe-rich and Cu-rich solid solutions necessary to stabilize the equilibrium aluminate phases (FeAl2O4 and CuAlO2, respectively) in the presence of α-Al2O3 are derived using data available in the literature. As in previous work in the Nisingle bondαsingle bondAl2O3 system, aluminate formation by solid state reaction of Fe and Cu with α-Al2O3 was calculated to require a threshold concentration of oxygen in the metal, which is of the order of 1/5 the solubility limit. The sults are presented in stability diagrams and compared with previous results on the Ni/α-Al2O3 system in terms of the free energies of formation of the aluminates and the relative free energes of solution of oxygen in the metals. The results are also compared with available experimental observations on Fe/α-Al2O3 and Cu/α-Al2O3 interfaces.

Résumé

On fait une revue des relations de phases ternaires au dessous du solidus can les syste`mes Fesingle bondAlsingle bondO et Cusingle bondAlsingle bondO afin d'obtenir une base pour une analyse thermodynamique de la formation d'aluminates aux interfaces Fe/Al2O3-α et Cu/Al2C2O3-α. Les expressions pour l'activite´critique de l'oxyge`ne dans les solutions solides en Fe et en Cu ne´cessaires pour stabiliser les phases 3luminates ene´quilibre (FeAl2O4 et CuAlO2 respectivement) en pre´sence de Al2O2-α sont obtenues en utilisant des donne´es disponibles dans la litte´rature. Comme dans un pre´ce´dent travail sur le syste`me Ni/Al2O3-α, on calcule que la formation d'aluminate par réactiona`l'état solide du Fe et du Cu avec Al2O3-α exige une concentration seuil d'oxyge`ne dans le me´tal, qui est de l'ordre de 1/5 de la solubilite´limite. Les re´sultats sont pre´sente´s dans des diagrammes de stabilite´et compare´s avec des re´sultats ante´rieurs sur le syste`me NiO/Al2O3-α,àpartir dese´nergies libres de formation des aluminates et dese´nergies libres relatives de solution de l'oxygeène dans me´taux. Les re´sultats sont compare´s aussi avec les observations expe´rimentales disponibles sur les interfaces Fe/Al2O3-α et Cu/Al2O3-α.

Zusammenfassung

Die Zusammenha¨nge zwischen den terna¨ren Phasen unterhalb der Soliduskurve in den Systemen Fesingle bondAlsingle bondO und Cusingle bondAlsingle bondO werden zusammengestellt, um eine Grundlage fu¨r die thermodynamische Analyse der Aluminatbildung an Fe/α-Al−2O3− und Cu/α-Al2O3-Grenzfla¨chen bereitzustellen. Es werden Ausdru¨cke anhand der in der Literatur verfu¨baren Daten abgeleitet fu¨r die kritischen Sauerstoffaktivita¨ten in den Fe- and Cu-reichen Mischkristallen, die fu¨r die Stabilisierung der Gleichgewichts-Aluminatphasen (FeAl2O4 und CuAlO2) in Anwesenheit von α-Al2O3 no¨tig sind. Wie in fru¨heren Arbeitenu¨ber das Ni/α-Al2O3-System zeigt die Rechnung zur Bildung von Aluminat durch Festko#x00A8;rperreaktion von Fe und Cu mit α-Al2O3, deβ eine Schwellkonzentration von Sauerstoff in dem Metall in der Gröβenordnung von 1/5 der Lo¨slichkeitsgrenze vorhanden sein muβ, damit die Reaktion ablaufen kann. Die Ergebnisse werden anhand von Stabilita¨tsdiagrammen darggstellt und verglichen mit fru¨heren Ergebnissenu¨ber das System Ni/α-Al2O3; Grundlage sind die freien Bildungsenergien der Aluminate und die relativen freien Lo¨sungsenergien des Sauerstoffes in den Metallen. Die Ergebnisse werden auβerdem mit verfu¨gbaren experimentellen Beobachtungen zu den Grenzfla¨chen Fe/α-Al2O3 und Cu/α-Al2O3 verglichen.

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    Present address: School of Materials Engineering, Purdue University, West Lafayette, IN 47907, U.S.A.

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