Microwave-Hydrothermal Synthesis of Monodispersed Nanophase α-Fe₂O₃

Synthesis of monodispersed nanophase α-Fe₂O₃ (hematite) powder to be used as a red pigment in porcelains was investigated using microwave-hydrothermal and conventional-hydrothermal reactions using 0.018M FeCl₃·6H₂O and 0.01M HCl solutions at 100°-160°C. Acicular and yellow β-FeOOH (akaganite) particles 300 nm in length and 40 nm in thickness were dominantly formed at 100°C after 2-3 h, while spherical α-Fe₂O₃ particles 100-180 nm in diameter were preferentially formed after 13 h using a conventional-hydrothermal reaction. However, a microwave-hydrothermal reaction at 100°C led to monodispersed and red α-Fe₂O₃ particles 30-66 nm in diameter after 2 h without the formation of β-FeOOH particles. In this paper, the effect of microwave radiation during hydrothermal treatment at 100°-160°C on the formation yield, kinetics, morphology, phase type, and color of α-Fe₂O₃ was investigated.