Formation mechanism of monodispersed α-Fe₂O₃ particles in dilute FeCl₃ solutions

Some ambiguity is still involved in the interpretation of the growth mechanism of monodispersed hematite (α-Fe₂O₃) particles in dilute FeCl₃ solutions. Namely, there are two entirely different proposals on this issue, viz. aggregation of preformed primary particles of α-Fe₂O₃ itself and reprecipitation of the ionic species through dissolution of the preformed β-FeOOH particles. In order to resolve this problem, the formation process was followed in detail through TEM, Electron Diffraction, XRD, FT-IR, and ICP spectrometry along with quantitative analyses on seed effects. As a result, it has been concluded that the nuclei of the hematite particles are initially generated with the formation of β-FeOOH particles and that they are grown by deposition of the solute originally present in the solution phase and indirectly furnished from the β-FeOOH by dissolution. As the concentration of the solute is lowered by the growth of the hematite particles, they continue to grow with the solute provided mainly from the β-FeOOH in a steady-state of the dissolution of β-FeOOH and growth of α-Fe₂O₃. The basic formation mechanism is common to the ellipsoidal particles grown in the presence of phosphate ions and spherical particles in their absence.