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

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 alpha-vredenburgite and jacobsite compositions had notably increased mean Al content compared to that of end-member Feor Mn-spinels. There was a strong negative correlation between the Fe+Al content and the Mn/Fe ratio of sinter jacobsite and of alpha-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 alpha-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.