Sonochemical powder processing of iron hydroxides

Iron (II) hydroxide was oxidized in an ultrasonic-activated solution to produce alpha-FeOOH (goethite) or Fe3O4 (magnetite). This process involves the dissolution of Fe(OH)(2), the oxidation of Fe2+ to Fe3+, and the precipitation of the products. It was found that the ultrasonic treatment greatly fasten the appearance and the growth of the products if oxygen was sufficiently supplied. When the oxygen supply was insufficient, on the other hand, an obvious phenomenon of sonochemical switching due to the enhanced oxidation was observed; that is, ultrasound promoted the alpha-FeOOH formation and suppressed the formation of Fe3O4 which has lower oxidation number (Fe = + 8/3) than alpha-FeOOH (Fe = + 3).