Microreactor synthesis of nanosized particles: The role of micromixing, aggregation, and separation processes in heterogeneous nucleation

The aim of the paper was to formulate the concept of controlled solution synthesis (a version of co-precipitation method) and to demonstrate its realization on several types of reactors, with a special focus on microreactors with free impinging jets (MRFIJ). The objects of this work are (i) co-precipitation method for synthesis of nanoparticles and (ii) various types of microreactors as a structured system consisting from dedicated elements. The procedure consisted on the decomposition of the total process into unit operations with further analysis of their spatial and temporal characteristics. It was shown that the elements for following unit operations should be presented in the microreactor: premixing; converging clusters (intense mixing in a thin layer/channel); ripening of nuclei; particle separation. Microreactors were shown as most appropriate devices for nanoparticles synthesis by co-precipitation method. Particularly, three case studies of co-precipitation synthesis in MRFIJ demonstrated possibility to produce nanoparticles having narrow particle size distribution (dmean: BiFeO3 – 20 nm, CoFe2O4 – 12 nm, GdFeO3 – 30 nm), without impurities of other phases and improved characteristics (e.g. low coercivity for GdFeO3 which makes it possible to use them as MRI-contrast agents) with high performance (4.3 m3/day). Besides, the temperature increase due to the energy dissipation in the liquid sheet in MRFIJ was analysed: it does not exceed 0.001 K and 0.2 K for characteristic jet velocities of 3.35 m/s and 40 m/s, correspondingly.