Continuous hydrothermal synthesis and crystallization of magnetic oxide nanoparticles

The continuous hydrothermal synthesis of nanoparticles of two metal oxides (α–Fe₂O₃ and Co₃O₄) is described. Two variations of the technique were investigated, involving the precipitation reaction between a metal salt solution and a hydroxide solution at ambient conditions and at elevated temperatures. Elevated temperatures resulted in more uniform particles of α–Fe₂O₃ and Co₃O₄, although the actual sizes of the particles were apparently unaffected by the temperature. This behavior was attributed to the species present in solution and the solubilities of the cation(s), both of which were calculated via a thermodynamic model for the systems under study.