Synthesis of Sr ferrite particle by supercritical hydrothermal synthesis

Sr ferrite nanoparticles were synthesized by supercritical hydrothermal synthesis. The precursor as a raw material was prepared by neutralizing a solution of iron nitrate (III) and strontium nitrate with KOH. First, a batch type reactor was used to explore the condition (temperature and reaction time) to synthesize Sr ferrite. As a result, formation of Sr ferrite was observed under supercritical water condition, 653 K and 10 min even though hematite was included in the product as impurities. However, all the hematite was changed to Sr ferrite when the reaction time was enlongated to 60 min. Particle size was around 1 μm. In the case of a flow system that can achieve rapid heating by mixing precursor with high temperature water, even at very shot reaction time Sr ferrite was synthesized in a single phase without any inpurity. It is because of the rapid heating system that could suppress the formation process of hematite at a lower temperature range. The particle size was as small as 200 nm, which is probably because of the extremely high supersaturation in supercritical state just after the rapid heating. Effect of synthetic parameters on microstructure for obtained Sr ferrite nano-materials was investigated. Magnetization characteristic of Sr ferrite nanoparticle synthesized by the flow-through supercritical water synthesizer was also evaluated.