Tomaž Kosmač^a and Mihael Drofenik^b

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

ABSTRACT

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.