Formation Mechanism of Ferrite Powders in Flux

Abstract

Ferrite formation has been studied in the presence of binary sulfate flux between 600°C and 900°C. Techniques employed are X-ray diffraction analysis, SEM and EPMA.
Mixtures of 0.365 N a₂SO₄-0.635 Li₂SO₄⋅H₂O and constituent oxides [Fe₂ O₃+MO(M Zn, Mg, Ni)] having various particulate characteristics were heated in a Pt crucible at desired tim etemperature conditions, followed by dissolving-out of flux with distilled water.
The flux lowered the temperature of ferrite formation by apprcdiniately 150 degrees regardless of the chemical species of MO(Fig.2). Morphology of ferrite powders so obtained depended on the relative particle sizes of the starting oxides; the combination of large Fe₂O₃ and small MO particles yielded ferrite powders which retained the shapes of the original Fe₂O₃ particles (Fig.5). Size reversal of the oxides, however, yielded ferrite powders with well-developed (111) planes (Fig.8). Two possible mechanisms have been proposed comprising with the relative dissolution rates of oxides into flux and they were confirmed by the experiments using sintered and compacted bodies of constituent oxides.