Thermodynamic properties of solid aluminium-iron alloys

The relative partial molar Gibbs energy Delta (G) over bar(Al) of Al was measured in the Fe-rich range (0.4 less than or equal to x(Fe) less than or equal to 1) of the Al-Fe system between 620 and 800 degrees C by the emf method using solid galvanic cells with a single-crystal Ca-F, electrolyte. The relative partial molar excess Gibbs energy of Al in Fe at infinite dilution is Delta(xs)(G) over bar(Al)(infinity) = -76 kJ/mol at 727 degrees C. The Gibbs energy of formation in the concentration range 0.36 less than or equal to x(Fe) less than or equal to 1 was obtained from Delta (G) over bar(Al) and from Delta (G) over bar(Fe) after Gibbs-Duhem integration and yields at 727 degrees C: Delta(f)G(0)[Al1.80Fe] = - 25 kJ/g-atom, Delta(f)G(0)[AlFe] = - 26.1 kJ/g-atom and Delta(f)G(0) [AlFe2.85] = - 18 8 kJ/g-atom. The composition Al1.80Fe is the Fe-rich phase boundary of Al2Fe at 727 degrees C. The composition AlFe2.85 is the Fe-rich end member of the CsCl type solid solution ranging between x(Fe) = 0.49 and 0.74. X-ray microanalysis of an Al0.241Fe0.759 sample annealed at 727 degrees C revealed a two-phase region with Al0.26Fe0.74 precipitates in the Al0.21Fe0.79 matrix which is the Al-rich end member of the W type AlxFe1-x solid solution at this temperature.