Self-propagating high-temperature synthesis of ferrites MFe2O4 (M = Mg, Ba, Co, Ni, Cu, Zn); reactions in an external magnetic field

Abstract

Spinel ferrites of the form MFe ₂ O ₄ (M = Mg, Co, Ni, Cu, Zn) and rhombohedral BaFe ₂ O ₄ have been prepared by self-propagating high-temperature synthesis (SHS) reactions from iron, cobalt, iron(III) oxide and metal(II) oxides or peroxides. The driving force for the reactions is the oxidation of iron or cobalt powder. Reactions were carried out in air, under an oxygen atmosphere or with the addition of sodium perchlorate as an internal oxidising agent. Reactions were also carried out in the presence of an external magnetic field of 1.1 T. Pre-organisation of the reaction mixture in the applied field led to increases in the reaction velocity (from 2 to 5 mm s ^–1 ) and temperature (950 to 1050 °C). The ratio of tetragonal to cubic phase observed for the CuFe ₂ O ₄ product was increased by carrying out the reaction in the applied field. The inversion parameter observed for MgFe ₂ O ₄ was also influenced by the applied field. All materials were characterised by X-ray powder diffraction (XRD), energy dispersive X-ray analysis (EDXA), scanning electron microscopy (SEM), FTIR, Mössbauer spectroscopy and vibrating sample magnetometry (VSM).