Preparation of monodisperse platelet-type hematite particles from a highly condensed β-FeOOH suspension

This is the first report on preparation of monodisperse platelet-type hematite (α-Fe₂O₃) particles. As an application of the gel-sol method recently developed by one of the authors for the syntheses of general monodisperse particles, monodisperse platelet-type hematite particles (≈3 μm in diameter, ≈0.6 μm in thickness) have been prepared by aging a highly condensed suspension of fine akaganeite (β-FeOOH) particles in a strongly alkaline medium at 70 °C for 8 days in the presence of a concentrated electrolyte. The yield was almost 100%. Each particle was bound by {001} basal planes and {012} side planes as identified by the oriented particulate monolayer-X-ray diffraction method. The formation of the characteristic shape has been explained in terms of the specific adsorption of OH^- ions. Systematic control of the mean size was shown to be possible by regulating the preparation temperature of Fe(OH)₃ gel as a starting material for β-FeOOH. The growth of the platelet-type hematite particles proceeded through a dissolution-recrystallization mechanism from β-FeOOH.