Continuous synthesis of fine MgFe2O4 nanoparticles by supercritical hydrothermal reaction

We produced magnesium ferrite (MgFe2O4) nanoparticles by hydrothermal synthesis in supercritical water. Suspensions containing varying ratios of Mg(OH)2 and Fe(OH)3 at room temperature were pressurized to 30 MPa, fed into a tubular reactor by high-pressure pump, and rapidly heated to reaction temperature by mixing with supercritical water. The MgFe2O4 phase forms at 460 °C. The Mg/Fe molar ratio was varied from 0.5 to 1.5 with the goal of obtaining single-phase MgFe2O4. At the stoichiometric ratio for MgFe2O4, Mg/Fe = 0.5, the product contains both MgFe2O4 and α-Fe2O3. At Mg/Fe = 1.0 and 1.5, the product is the desired single-phase MgFe2O4. The synthesized MgFe2O4 nanoparticles, with particle size of about 20 nm, exhibit superparamagnetic behavior.