Design and Processing of Hollow Ceramic Microspheres and Hybrid Ceramic/Polymer Microparticles

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Design and processing of hollow ceramic microspheres and hybrid ceramic/polymer microparticles were attempted as below.1. Preparation of ceramic microspheres by utilizing a mechanofusion system Core/shell structure was prepared by a mechanofusion system by employing several kinds of spherical polymers as a core material and Al_2O_3 powder or a mixture of Al_2O_3 and SiO_2 powder as a shell material. A large fraction of hollow alumina microspheres reflecting the shape and the particle size distribution of the core polymer could be fabricated after sintering at 1600℃ for 3h, when highly cross-linked PMMA microspheres with a gel fraction of ca. 99% were used as a core polymer and abrupt firing at temperatures higher than 500℃ was adopted to remove the PMMA microspheres. Titania microspheres were also prepared by employing the similar technique.2. Preparation of ceramic microspheres by utilizing a hybridization system Hybrid alumina/PMMA microparticles were prepared by utilizing a hybridiz … More ation system by employing PMMA microparticles and Al_2O_3 powder as a raw material. However, hollow microspheres were scarcely obtained even after calcination at 1600℃, because the Al_2O_3 powder could not be coated around the PMMA microparticles sufficiently.3. Preparation of ceramic microspheres by ultra-spray pyrolysis Alumina microsphreres were successfully fabricated by ultrasonic spraying of 0.5 M Al(NO_3)_3 aqueous solution, followed by instantaneous thermal decomposition and calcination at 1300℃. The crystal phase of as-prepared microspheres was δ-Al_2O_3, but turned into α-Al_2O_3 after post-calcination at 1300℃ for 2h. In addition, some microspheres were changed from solid to hollow structure by the post-calcination. The fraction of hollow microspheres in the resultant products was less than 30% and the mean diameter of these microspheres was 0.7 μm under these preparation conditions. However, the fraction could be increased up to 80% by the addition of a small amount of a surfactant to the precursor solution.4. Fabrication of aluminum/hollow alumina microspheres composites Aluminum/hollow alumina microspheres composites were fabricated by a liquid forging technique by employing aluminum ingot (ADC-12 ; Al>84.4%) and hollow alumina microspheres prepared by a mechanofusion system. The composites showed the highest flexural strength, compared with those prepared from commercially produced alumina bubbles, fly ash and silas balloons. Less