Critical process parameters and their interactions on the continuous hydrothermal synthesis of ironoxide nanoparticles

Conflicting reports exist about the critical process conditions for continuous hydrothermal synthesis of metal oxide nanopowders and are often accredited to the inability to isolate the effect of various operating parameters and the complexity of particle formation. In this study, an investigation was conducted on the effect of process parameters and their interactions during the continuous hydrothermal synthesis of hematite (α-Fe2O3) nanoparticles. Utilizing a 3-level, 3-factor Box-Behnken factorial design, the individual operating parameters (concentration, temperature and flow rate) and their interactions were evaluated. The interactions between operating parameters were found to be significant, especially in the case of temperature and concentration. The temperature and concentration were found to interact revealing three different trends on the average particle size, offering a solution to conflicting reports in the literature. The temperature was also observed to interact favourably with the flow rate, presenting a method of increasing the particle yield and relative crystallinity, with little change in average particle size or particle size distribution. This knowledge will prove invaluable for the design of future experiments in CHS.