Features and Importance of Solution Processing for Ceramics: Merits and Demerits of Precipitation Method. Colloids, Sol-Gel, Soft Chemistry, Soft (Solution) Processing and Others

摘要

Based upon thermodynamic considerations for materials processing, various solution processing methods appear to be the most energetically (environmentally) favorable techniques. Solution processing methods for ceramics are critically reviewed with emphasis on their merits and demerits. Confusion is pointed out in the definitions of various methods such as precipitation, colloid, sol-gel, polymer-gel, complexed-gel (polymerized complex), soft process (soft solution process) and/or more widely, solution deposition, chemical solution deposition, bio-mimetic, bio-inspired, ink-jet, spray, etc. In particular, for ceramic films and patterns, the conventional methods where firing is essential after coating of a solution precursor might be not far from solid (powder) processes. This is especially true when significant chemical reactions are not involved during the coating processes and most reactions such as pyrolysis, compound formation (synthesis), crystallization, consolidation, substrate adhesion, etc., occur in the solids by heat. Alternative methods where chemical reactions at the interface between a solution and a substrate solid and/or a reactant are described as typical Soft Processing Methods. In addition to the production of nano-crystals of SrTiO_3, Zr_(0.6)Ce_(0.4)O_2, etc., direct fabrication of LiCoO_2 and PbS films in solutions at room temperature to 150 deg C without post firing are described. "Direct Patterning of Ceramics" has also been proposed.