Tomaž Kosmača and Mihael Drofenikb

aJožef Stefan Institute, Jamova 39, SI-1000 Ljubljana, Slovenia
bFaculty for Chemistry and Chemical Engineering, University of Maribor, Smetanova 17, SI-2000 Maribor, Slovenia


Reaction-formed MnZn ferrite was prepared and the decrease in shrinkage after sintering due to the volume expansion accompanying iron oxidation was studied.
Green compacts consisting of the milled raw oxides Fe2O3, Mn3O4, ZnO and metallic iron powder were sintered at 1350 °C in air. During the first hold at 800 °C, Fe was oxidized to a-Fe2O3 and Zn ferrite was formed. Above 1300 °C the reaction bonding was completed and MnZn ferrite, exhibiting a relatively low shrinkage, was formed. The chemical reactions involved during reaction bonding were associated with a volume expansion and porosity formation, compensating for the shrinkage on sintering. Intensive milling decreases the porosity after sintering but induces the oxidation of iron, and partially removes the shrinkage compensation caused by the presence of metallic iron.