Reduction behaviour of Fe³⁺/Al₂O₃ obtained from the mixed oxalate precursor and the formation of the Fe⁰-Al₂O₃ metal-ceramic composite

Abstract

Reduction behaviour of Fe³⁺/Al₂O₃ obtained by the decomposition of the oxalate precursor has been investigated by employing X-ray diffraction (XRD), Mössbauer spectroscopy and electron paramagnetic resonance (EPR) spectroscopy. Calcination of Fe³⁺/Al₂O₃ at or below 1070 K yields mainly a poorly ordered, fine particulate form of η-Al_2-xFe_xO₃. Calcination at or above 1220 K yields α-Al_2−xFe_xO₃. Reduction of Fe³⁺/Al₂O₃ samples calcined at or below 1070 K gives the FeAl₂O₄ spinel on reduction at 870 K; samples calcined at or above 1220 K give Al_2−xFe_xO₃ with a very small proportion of metallic iron. Fe³⁺/Al₂O₃ samples calcined at 1220 K or above yield metallic iron and a very small proportion of the spinel on reduction below 1270 K. In the samples reduced at or above 1270 K, the main product is metallic iron in both ferromagnetic and superparamagnetic forms. The oxalate precursor route yields more metallic iron than the sol-gel route.