Abstract
Strong and subtle ultrasound was applied to a reacting solution and a starting solution, respectively, for ceramic powder preparation. The magnetite precipitation involves the dissolution of the initial precipitate of Fe(OH)2, the oxidation of Fe2+ to Fe3+, and the nucleation & growth. Effect of ultrasound was separatedly discussed at each stage. Two methods of ultrasonication, i.e., travelling wave and standing wave, were compared. Conspicuous difference of the two methods appeared when the initial concentration of Fe(OH)2, which decreases the particles size of magnetite, is as low as 0.001mol/l. That is, magnetite particles could not be formed under a strong macroscopic flow, even that made by a magnetic stirrer. However, 10nm-sized magnetite was successfully prepared by the standing wave treatment. Aparent transparency of a starting solution may include microscopic inhomogeneity which could be modified by aging or subtle ultrasonication. Effect of them on ceramic particles synthesis is discussed.
