Soft solution processing: concept and realization of direct fabrication of shaped ceramics (nano-crystals, whiskers, films, and/or patterns) in solutions without post-firing

Abstract

Based upon thermodynamic consideration for materials cycling and processing on the earth, where environmental and energetical problems have been seriously considered, we can conclude that solution processing using aqueous solutions should be the most important processing for advanced materials. According to the concept, we are proposing Soft Solution Processing (SSP) where advanced ceramics also must be preferably fabricated in solution(s) directly into desired composition, structure, shape, size, location, orientation, etc., in a closed system. This is contrasting to conventional processings where advanced ceramics have been fabricated from solids, liquids, and/or gases including atoms and/or ions in vacuum by sophisticated processes using high temperatures, high pressures, expensive precursors, and equipments. In most those processes, exhausted materials and heats have never cycled but just discarded into the environment. We have succeeded to prepare nanocrystals of ZrO₂, HfO₂, HAp, BaTiO₃, CeO₂/ZrO₂, LiCoO₂, CdS, etc., whiskers of HAp, and films of BaTiO₃, SrTiO₃, CaWO₄, BaMoO₄, YVO₄, LiCoO₂, LiNiO₂, ZnFe₂O₄, etc., in solutions at low temperatures of RT-150°C. Recently, the fabrication of patterned films for LiCoO₂, PbS, CdS, BaTiO₃, SrTiO₃, etc., have also been succeeded in/from solutions at the low temperatures. Those “Direct Patterning of Ceramics” should be soft in comparison with conventional ceramic patterning where multi-steps like firing, sintering, masking, etching, etc., are required even after synthesizing ceramic powders.