Synthesis of ferrite grade gamma-Fe2O3

Abstract

Iron(II) carboxylato-hydrazinates: Ferrous fumarato-hydrazinate (FFH), FeC4H2O4.2N(2)H(4); ferrous succinato-hydrazinate (FSH), FeC4H4O4.2N(2)H(4); ferrous maleato-hydrazinate (FEH), FeC4H2O4.2N(2)H(4); ferrous malato-hydrazinate (FLH), FeC4H4O5.2N(2)H(4); ferrous malonato-hydrazinate (FMH), FeC3H2O4.1 .5N(2)H(4).H2O; and ferrous tartrato-hydrazinate (FTH), FeC4H4O6.N2H4.H2O are being synthesized for the first time. These decompose (autocatalytically) in an ordinary atmosphere to mainly gamma -Fe2O3, while the unhydrazinated iron(II) carboxylates in air yield alpha -Fe2O3, but the controlled atmosphere of moisture requires for the oxalates to stabilize the metastable gamma -Fe2O3. The hydrazine released during heating reacts with atmospheric oxygen liberating enormous energy, N2H4 + O-2 to N-2 + H2O; DeltaH(2)O = - 621 kJ/mol, which enables to oxidatively decompose the dehydrazinated complex to gamma -Fe2O3. The reaction products N-2 + 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 gamma -Fe2O3 in the ferrite synthesis.