Microstructure control of functional ceramics ih double oxide system by homogeneous solution methods

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Excellent properties of functional ceramics have been attained by forming multinary oxides, Their preparation in soft solution process may lead to new meta-stable layered compounds having several kinds of stacking structural units with different properties. This process can also be applied to their micro-structure control. In the present study, we have developed two kinds of the following new soft solution process.(1) Citric acid was added to the mixed aqueous solution of metal nitrates as its geling agent The firing of the gel at 350℃ lead to combustion synthesis of fine powder of functional ceramics with a diameter of less than 100 nm. This process was applied to transparent conducting (ZnO)_3In_2O_3 and also to barium hex ferrite. Usage of EDTA or acetylacetonate complex was effective to avoid inhomogeniety due to the hydroxide formation of a component. This combustion synthesis was also useful to obtain zirconia coated alumina powder.(2) Microgravity condition was applied during freezing of aqueous solution of mixed metal salts. Dendritic ice was formed in this process. The frozen products were freeze dried in vacuum. Relative x-ray intensity of hh0 lines was enhanced in tetragonal crystal strictures ofZrOCi_2・8 H_2O and AlCl_3 6 H_2O. Liner complex ion units ordered much better under microgravity than in ambient condition. Improved homogeniety was observed on the precipitated metal salts in the dendritic ice in comparison to the salts obtained from the frozen product in ambient condition. The homogeniety was effective to obtain double oxide in high yield.