Thermodynamic properties of solid aluminium-iron alloys

The relative partial molar Gibbs energy Δ anti GAl of Al was measured in the Fe-rich range (0.4 ≤ χFe ≤ 1) of the Al-Fe system between 620 and 800 C by the emf method using solid galvanic cells with a single-crystal CaF2 electrolyte. The relative partial molar excess Gibbs energy of Al in Fe at infinite dilution is ΔXS anti G∞Al = -76 kJ/mol at 727 C. The Gibbs energy of formation in the concentration range 0.36 ≤ χFe ≤ 1 was obtained from Δ anti GAl and from Δ anti GFe after Gibbs-Duhem integration and yields at 727 C: ΔfG0 left angle Al1.80Fe right angle = -25 kJ/g-atom, ΔfG0 left angle AlFe right angle = -26.1 kJ/g-atom and ΔfG0 left angle AlFe2.85 right angle -18.8 kJ/g-atom. The composition Al1.80Fe is the Fe-rich phase boundary of Al2Fe at 727 C. The composition AlFe2.85 is the Fe-rich end member of the CsCl type solid solution ranging between χFe = 0.49 and 0.74. X-ray microanalysis of an Al0.241Fe0.759 sample annealed at 727 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. (orig.)