Occurrence of Strontium–Iron Oxide SrFe12O19 in the Fe2O3–Na2O–SrSO4 System

The formation of SrFe 12 O 19 in the Fe 2 O 3 –Na 2 CO 3 –SrSO 4 system was found to proceed through three stages, first an endothermic reaction between Fe 2 O 3 and Na 2 CO 3 to form Na 2 Fe 2 O 4 and CO 2 , second an exothermic reaction of Na 2 Fe 2 O 4 with SrSO 4 to produce Na 2 SO 4 , Sr 7 Fe 10 O 22 , and SrFe 12 O 19 , third an exothermic reaction between Sr 7 Fe 10 O 22 and Fe 2 O 3 towards more SrFe 12 O 19 . The yield of SrFe 12 O 19 depended on the molar ratio of the reactants and on temperature. Below 700 °C the formation did not proceed beyond the second stage. Samples prefired at 900–1200 °C contained SrFe 12 O 19 in all cases when the original relative molar concentrations xFe 2 O 3 ,yNa 2 CO 3 , and zSrSO 4 satisfied the condition (x − y + z)/z > 5/7 or x/y > 5/7 ≥ x/z. Substitution of Na 2 CO 3 in the reaction mixtures with equivalent amounts of NaOH or other precursors of Na 2 O did not affect the second and the third stage of the reaction and the final yield of SrFe 12 O 19 . On the ternary diagram of the Fe 2 O 3 –Na 2 O–SrSO 4 system the SrFe 12 O 19 region was represented by the area of a quadrilateral with the corner points located at the composition points 98-1-1, 1-1-98, 26-36-38, and 50-49-1 mole percent. The highest yields were obtained from the mixtures represented by the molar ratio 6Fe 2 O 3 :1 Na 2 O:1SrSO 4 . The hexagonal lattice parameters of SrFe 12 O 19 were determined as a 0  = 5.885 Å and c 0  = 23.047 Å. X-Ray diffraction reflections of SrFe 12 O 19 were indexed and reassignment of several indices in ASTM 7-276 for BaFe 12 O 19 was suggested.