Microhardness-compositional relationship of Fe₃O₄-Mn₃O₄ series spinels from ferromanganese sinter and its relationship to sinter strength

ABSTRACT

Fe-Mn spinels are common bonding phases in ferromanganese sinter and play an important role in determining sinter strength. This study analysed spinel phases from ferromanganese sinter to determine the range of compositions present and examine the relationship between phase composition and microhardness. Spinels with α-vredenburgite and jacobsite compositions had notably increased mean Al content compared to that of end-member Fe- or Mn-spinels. There was a strong negative correlation between the Fe+Al content and the Mn/Fe ratio of sinter jacobsite and of α-vredenburgite, indicating the likely substitution of Al³⁺ for Mn³⁺ in the vredenburgite structure. Mixed Fe-Mn spinels had higher Vickers and Knoop microhardness and fracture toughness than end-member Fe- or Mn-spinels. It is likely that the presence of Al in the octahedral site in the α-vredenburgite structure is related to the increased microhardness and, therefore, should have a positive effect on sinter strength if vredenburgite is present in sufficient quantities.

KEYWORDS:

• Ferromanganese sinter
• sinter strength
• Fe-Mn spinels
• α-vredenburgite
• microhardness
• electron probe microanalysis

Acknowledgments

The authors thank CSIRO Mineral Resources for funding the work and for permission to publish. Bureau Veritas are acknowledged for XRF analysis, Peter Self and Mark Raven from CSIRO Land and Water are acknowledged for qualitative XRD analysis and Dr Mark Pownceby for reviewing a draft of the manuscript. The authors would also like to acknowledge the two anonymous journal reviewers and the editor for their helpful suggestions.

Disclosure statement

No potential conflict of interest was reported by the author(s).