Continuous supercritical hydrothermal synthesis of iron oxide nanoparticle dispersions and their characterization

Electrostatically stabilized iron oxide nanoparticle dispersions were synthesized using a continuous hydrothermal process at 673 K and 30 MPa. The average size of the primary particles was in the range 5-30 nm. The influence of the flow conditions as well as the composition of the starting material on the dispersion properties was investigated. A new Raman spectroscopic measurement setup was used for the characterization of the structure of the nanoparticles in dispersed form. The use of differential centrifugal sedimentation for the determination of the size distribution of the dispersed particles proved to be convenient and powerful to determine the influence of the investigated parameters on the dispersion properties. For certain compositions of the starting material and flow conditions using a conventional T-union, narrow size distributions concerning both primary particles and agglomerates could be obtained.