Hydrothermal Synthesis of Advanced Ceramic Powders

This paper briefly reviews hydrothermal synthesis of ceramic powders and shows how understanding the underlying physico-chemical processes occurring in the aqueous solution can be used for engineering hydrothermal crystallization processes. Our overview covers the current status of hydrothermal technology for inorganic powders with respect to types of materials prepared, ability to control the process, and use in commercial manufacturing. General discussion is supported with specific examples derived from our own research (hydroxyapatite, PZT, 􀄮-Al2O3, ZnO, carbon nanotubes). Hydrothermal crystallization processes afford excellent control of morphology (e.g., spherical, cubic, fibrous, and plate-like) size (from a couple of nanometers to tens of microns), and degree of agglomeration. These characteristics can be controlled in wide ranges using thermodynamic variables, such as reaction temperature, types and concentrations of the reactants, in addition to non-thermodynamic (kinetic) variables, such as stirring speed. Moreover, the chemical composition of the powders can be easily controlled from the perspective of stoichiometry and formation of solid solutions. Finally, hydrothermal technology affords the ability to achieve cost effective scale-up and commercial production.