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

本研究的最终目标是在低于莫来石共晶温度的较低温度下烧结微空心球颗粒，制备具有高韧性的高性能莫来石陶瓷复合材料。然而，本研究的结果主要集中在通过喷雾干燥分子设计的前驱体溶液制备精细莫来石空心球，以及超细莫来石前驱体粉末的烧结行为。结果总结如下：(1)莫来石空心微珠的制备条件：喷雾干燥条件对制备的莫来石空心微珠的形貌有影响。结果表明，喷嘴直径对粉末形貌有较大影响。小尺寸的喷嘴是制备微球颗粒的必要条件。前驱体溶液的醇盐浓度和溶剂的种类也有效地控制了所得粉体的形貌。结果表明，i-丁醇是制备微球的最佳条件。所得前驱体粉末的结晶行为不随前驱体溶液的制备条件而改变。它们在1200℃以上结晶成化学计量莫来石。然而，随着醇氧化合物浓度的增加，晶粒大小发生了变化。(2)前驱体粉末的低温烧结：将前驱体溶液用小喷嘴喷雾干燥，以i-丁醇为溶剂，可制得含有莫来石成分的空心前驱体粉末。制备的前驱体在800℃的温度下煅烧，去除残留的有机物，得到低密度的绿色压坯。这阻碍了空心细颗粒的低温烧结。烧结助剂和热等静压对制备致密复合材料的力学性能没有改善。

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.