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The formation of strontium hexaferrite SRFE 12 O 19 from pure iron oxide and strontium carbonate has been studied by means of dynamic high temperature X-ray diffraction, thermal analysis, and thermogravimetry. The formation in air passes through two endothermal reactions: SrCo 3 +6α-Fe 2 O 3 + (0. 5-x) 12 O 2 → SrCo 3 +5. 5α-Fe 2 O 3 +CO 2 (A) SrFeO 3-x +5. 5α-Fe 2 O 3 → SrFe 12 O 19 + (0. 5-x) 12 O 2 (B) The solid state reaction of the formation of the perovskite SrFeO 3-x starts between 660 C (0. 13°/min) and 730 C (20°/min) depending on the heating rate. Above 810 C or 1000 C, resp. , the perovskite reacts with the excess iron oxide forming the hexaferrite. During the process a part of the iron becomes tetravalent and is again reduced into the trivalent state. The phase Sr 7 Fe 10 O 22 or Sr 4 Fe 6 O 13, resp. , observed in quenched samples could not be detected during the formation in air.
Haberey et al. (Mon,) studied this question.