Preparation of Ceramic Composites with High Toughness by Low-temperature Sintering of Micro-hollow Sphere Particles

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The final goal of this research is the preparation of the high performance mullite ceramic composites with hightoughness by sintering the micro-hollow sphere particles at relatively low temperature below a eutectic temperature of mullite. However, the results of this research mainly focused on the preparation of fine mullite hollow spheres by spray-drying the molecular-designed precursor solution as well as the sintering behavior of the ultra-fine mullite precursor powders.The results were summarized as follows ;(1) Preparation Condition for Fine Mullite Hollow Sphere : The morphology of the resulting powders were affected by the spray-drying condition. It was conluded that the nozzle diameter had large effect on the morphology of the resulting powders. Small size nozzle was essential for the preparation of the micro-sphere particles. Alkoxide concentration of the precursor solutions and the kind of a solvent also effectively control the morphology of the resultant powders. As a ewsult, i-butyl alcohol offered the best condition for the micro-sphere preparation. The crystallization behavior of the resultant precursor powders did not change with the preparation condition of the precursor solutions. They crystallized into a stoichiometric mullite above 1200ﾟC.However, the crystallite size changed with the alkoxide concentration.(2) Low-temperature-sintering of the Precursor Powders : Fine hollow precursor powders with mullite composition could be prepared by spary-drying the precursor solution using small size nozzle and i-butyl alcohol as a solvent. The resultant precursors were calcined at 800ﾟC to remove the residual organics, resulting in the low-density green compacts. This detered the low-temperature-sintering of the fine hollow particles. Sintering aid and hot-isostatic-pressing were needed to prepare the dense composites, which did not improve the mechanical properties.