Synthesis of functional ceramic materials from aqueous solutions
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Synthesis of functional ceramic materials from aqueous solutions Takeshi Yao Department of Fundamental Energy Science, Graduate School of Energy Science, Kyoto University, Yoshida, Sakyo-ku, Kyoto-shi 606-01, Japan (Received 17 September 1997; accepted 15 January 1998)
Methods for synthesizing ceramic materials from aqueous solutions at ordinary temperature and pressure are advantageous because of the applicability to making films with wide areas and/or complicated shapes with no requirement of vacuum or high temperature, and because of lower cost. Powder of ZrO2 or LnMeO3 (Ln La, Nd; Me Cr, Mn, Fe, Co) perovskite was dissolved in hydrofluoric acid and a solution of fluoro-complex ions was obtained. Boric acid was added to the solution, the fluoride ions were consumed by the formation of BF4 2 , and then the fluoro-complex ions were hydrolyzed to ZrO2 or LnMeO3 in order to increase the amount of fluoride ions. A number of synthesized particles of ZrO2 or LnMeO3 were observed on the substrates in scanning electron microscope images.
I. INTRODUCTION
Functional ceramic materials relating to zirconium oxide or rare-earth transition metal perovskite oxides have many technological uses including such as oxygen sensors,1,2 catalysts,3 electrocatalysts,4–6 oxygen permeating membranes,7,8 and materials for high-temperature steam electrolysis cells.9 They are also drawing attention as solid state electrolyte, cathode, or interconnection materials for solid oxide fuel cells,10 which are major candidates for energy generating systems in the near future. Thin films, either dense or porous, are desirable because of the high surface area, the reduction of both the ion-diffusion path length and electrical resistance, the light and compact system construction, and so on. Chemical vapor deposition, sputtering and sol-gel methods are used for preparing thin films; however, these methods have some disadvantages in actual use. For chemical vapor deposition and sputtering, expensive vacuum equipment is required and the film area is restricted. For the sol-gel method, the film geometry is limited, and moreover, heat treatment, which is injurious because of the possibility of a change in the shape and/or size of the film and crack formation, is required to form crystalline states. A method for forming films from an aqueous solution is expected to be advantageous because no vacuum, no high temperature, and J. Mater. Res., Vol. 13, No. 5, May 1998
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no expensive apparatus will be required, and substrates, even those with wide areas and/or complicated shapes, are available; however, the possibility had not been studied earnestly. On the other hand, if we look around in nature, we can easily find many kinds of ceramics synthesized from aqueous solutions such as our bones,11 shells, eggshells, and so on. From this point of view, we believed it possible to synthesize functional ceramics from aqueous solutions, and we investigated the metho
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