Effect of ultrasound on the dissolution-precipitation process in the aluminum hydroxide-water system

Precipitation and ripening of an amorphous aluminogel in an aqueous solution were subjected to irradiation of ultrasound with various intensities at different frequencies. For comparison with the ripening of aluminogels, hydration of amorphous alumina powder in ultrasonic-driven water was studied. It was found that an intensive ultrasound during ripening decreased the relative amount of bayerite, which is a product in the ripening of the amorphous gels, whereas, a moderate ultrasound during ripening increased the relative amount of bayerite. On the other hand, the relative amount of bayerite increased when the gels were precipitated ultrasonically and ripened normally. The role of ultrasound in the ripening (dissolution-precipitation) process is discussed.