Hydrothermal synthesis of zirconia nanocrystals in supercritical water
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Tomotugu Ohashi Graduate School of Environmental Studies, Tohoku University, Aramaki Aza Aoba 07, Aoba-ku, Sendai 983-8551, Japan
Hiromichi Hayashi Supercritical Fluid Research Center, National Institute of Advanced Industrial Science and Technology (AIST), Nigatake 4-2-1, Miyagino-ku, Sendai 983-8551, Japan
Kunio Arai Graduate School of Environmental Studies, Tohoku University, Aramaki Aza Aoba 07, Aoba-ku, Sendai 983-8551, Japan (Received 3 February 2004; accepted 18 May 2004)
Zirconia nanocrystals were prepared by hydrothermal reaction of 0.05 M zirconyl nitrate and zirconyl acetate solutions at supercritical conditions of 400 °C and 30 MPa for 1.8 s reaction time. Characterization of products were performed by x-ray diffraction, transmission electron microscopy, and Brunauer–Emmett–Teller measurements. The product particles were compared with zirconia particles prepared by conventional hydrothermal synthesis routes and precipitation-calcination. From the results, zirconia powders prepared in supercritical water had higher crystallinity than those obtained by other methods. Product particles with tetragonal crystal structure with a mean diameter of 6.8 nm could be formed from 0.05 M zirconyl acetate solution in the presence of 0.1 M potassium hydroxide at supercritical conditions. I. INTRODUCTION
Zirconia particles and related ceramics are used widely in the field of industrial materials in applications such as polishers, pigments, catalysts, refractory materials, electric materials, solid oxide fuel cells, and structural materials due to their specific chemical and physical properties, including high chemical stability, high temperature insulation ability, and ionic conductivity. The chemical and physical performance of zirconia ceramics is determined by characteristics of zirconia particles such as size and crystallinity.1 The nonaggregated and highly crystalline particles with less than 10 nm in diameter are desirable for fabricating high-performance nanophase ceramics. Zirconia particles are prepared commercially by precipitation2 or hydrolysis methods.3 Several methods for producing zirconia nanocrystalline powders have been developed such as combustion,4 hydrothermal synthesis,5–8 sol-gel,9,10 and polymer template methods.11 a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2004.0314 2230
http://journals.cambridge.org
J. Mater. Res., Vol. 19, No. 8, Aug 2004 Downloaded: 19 Nov 2014
Hydrothermal routes have been promoted for many years for the production of fine zirconia particles used in electrical applications as reviewed by Somiya and Akiba.12 These methods have been very successful in preparation of fine particles but thus far have been limited to particle sizes having diameters in the submicron range and generally produce aggregates. To obtain crystalline nanoparticles, methods that can restrain particle growth during crystallization are needed. In other words, it would be preferable to terminate crystallization as early as possible after nucleation by c
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