Ultrasonic synthesis of ceramic materials: Fundamental view #13

This article is concerned with fundamental materials systems consisting of commonplace or ubiquitous elements (Si, O, Al, Fe, etc.), aiming at how to draw out the novel potentiality of sonochemistry to ceramic processing rather than to reach hurriedly to modern functional materials in popularity. Silica sphere synthesis is a main topic discussed in detail. Ultrasonication during the synthesis caused a curious agglomeration presumably due both to an ultrasonic-induced collision and to surface activity of silica spheres. Another type of sonication at very low intensity is newly proposed here to enhance the aging of starting solutions. This novel concept is based on a hypothesis that microscopic homogeneity is not guaranteed in a transparent solution. In the experimental facts, the aging of the starting solutions results in a delay of precipitation, narrowing of sphere size distribution, and increase of sphere size (i.e., decrease of nucleus number), which can be attributable to an increased microscopic homogeneity in the starting solutions. Other fundamental systems presented are crystallization from a supersaturated solution of alum (ammonium aluminum sulfate hydrate), solidification of molten inorganic salts (nitrate binary), and dissolution in and reprecipitation from a mother solution (ripening of aluminogels and oxidation of magnetic nanoparticles).