Nanoparticulate Coating of Functional Ceramics by the Vapor, Solid and Liquid Phase Reactions
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ABSTRACT Microstructure control of ceramics is expected to produce novel functions or to improve properties. Nanocomposite powders of functional ceramics were fabricated by vapor, solid and liquid phase reactions, respectively. Superconducting bulk materials were fabricated by thermal plasma method and mist pyrolysis method. Microstructure control of powders for sintering contributed to improve the microstructure at grain boundaries and to introduce magnetic flux pinning centers, both resulted in the improvement of superconducting transport current property. On the other hand, a magnetic nanocomposite for the remote sensing of stress in structural ceramics was fabricated by sol-gel method and solid state reaction. Successfully introduced nano-dispersoids of ferromagnetic materials by the sintering of nanocomposite powders resulted in the harmonization of added functionality and proper mechanical properties. Magnetic response to applied stress in structural ceramic matrix was detected as the result of amplified magnetostriction caused by the nano-size effect on ferromagnetic dispersoids. INTRODUCTION Oxide superconductors will be used for electric devices applications as films, for power electronics as wires, especially for various applications for its magnetic properties as bulk shape. Elimination of weak-link structure at grain boundaries' and introduction of pinning centers for magnetic flux2 are the most important problems to be solved before the usage especially as bulk. Fine, microstructure controlled powders as raw material in the sintering process of bulk, is required to control microstructure of resulting bulk ceramic bodies3 . Thermal plasma method 4' 5 and mist pyrolysis method 6 have been expected for their ability to synthesize fine powders and films of ceramics by the vapor phase reaction. On the other hand, development of novel materials with harmonization of functional and structural properties has been desired to spread applications of ceramics based materials by enhancing reliability7,8 . Nanocomposite ceramics have been developed to improve mechanical properties on both of fracture strength and toughness9"(, which were contradicted each other in ordinary microstructure control technique. "Synergy ceramics" is the new concept for development of the innovative materials by synergitic effects caused by the structure control on multi-scale level1 . Remote sensing of stress applied on a structural ceramic is an approach to enhance the reliability of "brittle" ceramics by the prediction and prevention of catastrophic fracture by monitoring it in practical circumstance for temperature, atmosphere and non-static mode12 . Mechanical grinding process combining with liquid phase reaction such as sol-gel method is effective to fabricate a nanocomposite which has difficulty on synthesis because of unexpected chemical reaction. In this paper, applications of vapor, solid and liquid phase reactions for the synthesis of composite powders of an oxide superconductor to fabricate microstructure controlled bulk 339 M
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