Preparation of Strontium Ferrite Particles by Spray Pyrolysis

Abstract

Crystalline, submicrometer strontium ferrite powders, including SrFeO 2.97 , SrFe 2 O 4 , Sr 2 FeO 4 , Sr 3 Fe 2 O 6.16 , and SrFe 12 O 19 , were prepared by spray pyrolysis of an aqueous solution of mixed metal nitrates. The Sr:Fe mole ratio in the precursor solution was retained in the final products. Phase‐pure materials were typically obtained only at the highest temperatures investigated (>1100°C) and powders prepared at lower temperatures frequently contained crystalline Fe 2 O 3 . The as‐prepared particles were unagglomerated, polycrystalline, and hollow at lower temperatures, but densified in the gas phase at higher temperatures to give solid particles. The strontium ferrite (SrFe 12 O 19 ) system was studied in detail as a representative example of the Sr‐Fe‐O system. At temperatures of 1200°C, dense, phase‐pure magnetoplumbite‐structure material, SrFe 12 O 19 , was obtained, while at lower temperatures, small amounts of Fe 2 O 3 were observed. The particles prepared at 800° and 1100°C were 0.1‐1.0 μm in diameter, and consisted of crystallites <100 nm, and were nearly solid. The difficulty in forming phase‐pure SrFe 12 O 19 was the different thermal decomposition temperatures of Sr(NO 3 ) 2 (725°C) and Fe(NO 3 ) 3 9H 2 O (125°C) as demonstrated by thermogravimetric analysis in the SrFe 12 O 19 system.