Formation of manganese- and manganese,zinc-bearing ferrites by oxidation of aqueous suspensions and analysis of their cation distributions

Abstract

Oxidized manganese-bearing and manganese,zinc-bearing ferrites have been prepared by air oxidation of iron(II) hydroxide suspensions at initial Mn:Fe tot mol ratios ( r Mn) of 0.20:2.80 to 1.40:1.60 and initial (Mn + Zn):Fe tot mol ratios ( r Mn+Zn) of 0.20:2.80 to 1.00:2.00, respectively, at pH 10.0 and 65°C. Mössbauer spectra at room temperature and chemical analysis of the manganese-bearing ferrites suggest that Mn 2+ ions are incorporated into the tetrahedral sites in the ferrites with manganese compositions of less than 0.74 and into both the tetrahedral and the octahedral sites at compositions of 0.74 to 1.06. In addition, manganese ions in a higher valence state than 3+ are incorporated into the octahedral sites at manganese compositions above 0.74. Mössbauer spectra at room temperature of the manganese,zinc-bearing ferrites prepared at r Mn+Zn = 1.00:2.00 indicate that Mn 2+ ions are incorporated on the lattice points in the ferrites and in both the tetrahedral and the octahedral sites at manganese compositions of 0.33 to 0.51. Mössbauer spectra and chemical analysis also suggest the incorporation of manganese ions in valence states higher than 3+. Mössbauer spectra and the lattice constants imply that the octahedral lattice sites in the ferrites with manganese compositions equal to or greater than 0.51 are distorted. Mössbauer spectra at room temperature of the manganese,zinc-bearing ferrites prepared at r Mn+Zn = 0.20:2.80 to 0.80:2.20 suggest that Mn 2+ ions are incorporated into both the tetrahedral and the octahedral sites in the ferrites, and that the amounts of Mn 2+ ions on the octahedral sites increase with increases in the manganese composition of the ferrites prepared at each r Mn+Zn value.