Synthesis of ferrite grade γ-Fe2O3

Abstract

Iron(II) carboxylato-hydrazinates: Ferrous fumarato-hydrazinate (FFH), FeC4H2O4·2N2H4; ferrous succinato-hydrazinate (FSH), FeC4H4O4·-2N2H4; ferrous maleato-hydrazinate (FEH), FeC4H2O4·2N2H4; ferrous malato-hydrazinate (FLH), FeC4H4O5·2N2H4; ferrous malonato-hydrazinate (FMH), FeC3H2O4·1·5N2H 4·H2O; and ferrous tartrato-hydrazinate (FTH), FeC4H4O6·N2H 4·H2O are being synthesized for the first time. These decompose (autocatalytically) in an ordinary atmosphere to mainly γ-Fe2O3, while the unhydrazinated iron(II) carboxylates in air yield α-Fe2O3, but the controlled atmosphere of moisture requires for the oxalates to stabilize the metastable γ-Fe2O3. The hydrazine released during heating reacts with atmospheric oxygen liberating enormous energy, N2H4 + O2 → N2 + H2O; ΔH2O = - 621 kJ/mol, which enables to oxidatively decompose the dehydrazinated complex to γ-Fe2O3. The reaction products N2 + H2O provide the necessary atmosphere of moisture needed for the stabilization of the metastable oxide. The synthesis, characterization and thermal decomposition (DTA/TG) of the iron(II) carboxylato-hydrazinates are discussed to explain the suitability of γ-Fe2O3 in the ferrite synthesis.