Synthesis of SrFeO_2.5 from mechanically activated reactants

The influence of high-energy ball milling of reactants on a heat activated synthesis of SrFeO_2.5 from hematite and strontium carbonate was investigated by X-ray diffraction and thermogravimetric analysis. According to our study the temperature and time required for the reaction can be significantly lowered by ball milling of reactants. A wet mechanical processing of the mixture is the fastest way to reduce the size of reactants' grains and therefore bring the temperature down. Apart from this, milling causes partial transformation of hematite to magnetite, which results in a smaller mass loss of the samples during calcination. However, SrFeO_2.5 is synthesized together with some transient phases that finally vanish. This equilibration process is much faster in ball milled samples than in specimens prepared by the traditional ceramic method as a result of the higher homogeneity of the milled ones.