新素材：環境・エネルギー材料の新展開 セラミックスを溶液から作る意味と意義―ナノ粒子，薄膜，厚膜，パターンおよびバルク体―

Abstract

Based upon thermodynamic considerations for various materials processing, solution processings appear to be the most energetically (environmentally) benign techniques. Various solution procesings for ceramics are critically reviewed with emphasis on their merits and demerits. Existing confusions and contradictions are pointed out in the definitions and concepts of various methods: i.e. 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 powders from their suspensions or their solution precursors might be rather close to solid (powder) processes. This is especially true when significant chemical reactions are not involved during the coating processes, thus most reactions such as pyrolysis, compound formation (synthesis), crystallization, consolidation, substrate adhesion, etc., occur in the solid states by heat. In those solid state processes using firing of powders after shape-forming, the cracking/peeling of the film and/or the bulk is serious problems because volume shrinkage during firing is inevitable for packed powders. Those shrinkages practically limit the application of those powder processes. In order to overcome those limitations, alternative methods where chemical reactions at the interface between a solution and a substrate solid and/or a reactant are described here as typical Soft Processing Methods. They may lower the difficulties in powder processes by forming shaped materials in a single step at lower temperatures. In addition to the production of nano-crystals such as SrTiO3, Zr0.6Ce0.4O2, etc., direct fabrication of LiCoO2 and PbS films in solutions at room temperature to 150°C without post firing are described. “Direct Patterning of Ceramics” using ink-jet reaction or ink-jet deposition method has also been proposed.