Monitoring in real time the production of Fe-oxide nanoparticles

•Assessment to the vital stages of Fe-oxide NPs’ formation by coprecipitation.•AC susceptometer to monitor in real time the magnetic response of the mixing volume.•Nucleation, growth and diffusion identified on the in- and out-phase signals.•Mixing reactants with pitch blade impellers allow narrow particle size distribution .

We herein demonstrate an in-situ device and a real time method to observe the vital stages of Fe-oxide nanoparticles’ (NPs) preparation by coprecipitation reaction. The reaction volume is monitored by a home-made AC susceptometer to analyze the magnetic response of the growing NPs. Three different regions (nucleation, growth and diffusion) could be identified in the recorded in-phase and out-of phase curves. The morphological and magnetic characterization of the obtained Fe-oxide NPs reveal minute particle dimensions (<3 nm), narrow polidispersity (1–7 nm), superparamagnetic behavior (null coercivity) and narrow distribution of blocking temperatures (~67 K). We show that the device and technique enable real time assessment of the mixing speed which has paramount impact on the physical and chemical properties of the final product.

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