Thermal transformations of natural jacobsite (Mn, Fe)₃O₄

Abstract

Mössbauer spectroscopy and x-ray powder diffraction have been used to study the natural manganese ferrite known as jacobsite (Mn, Fe)3O4, after calcination at temperatures varying from 400°C up to 1160°C. Calcination at temperatures between 400°C and 900°C results in the formation of haematite and bixbyite (Mn, Fe)2O3. The room temperature Mössbauer spectra of samples calcined above 900°C indicate that the haematite and the bixbyite transform, as the calcination temperature is increased, gradually into synthetic manganese ferrite. The results suggest that Mössbauer spectroscopy of ferrites can supply information about the thermal history of such samples.

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“…The Mössbauer data collected on the different samples are presented in Figure 14(a). The spectrum of sample B clearly shows the presence of a magnetic signal, mainly made of two different sextets; the corresponding hyperfine magnetic fields (HF) are B HF,1 ¼ 45.0 ± 0.1 T and B HF,2 ¼ 48.63 ± 0.05 T. As this sample was produced using both Fe and Mn diketonates with a 2:1 ratio, for comparison we may use the HF values measured for magnetite (Diamandescu et al, 1998) and for the natural and synthetic Manganese Ferrite (namely Jacobsite, MnFe 2 O 4 ) (Araujo et al, 1989;Maia et al, 1993). The found HF values and the relative ratio of the sextets areas are closer to those expected for magnetite, indicating that the NPs relative Mn concentration is smaller than that found in the starting mixture.…”