Characterization of CeO 2 Fine Particles Prepared by the Homogeneous Precipitation Method with a Mixed Solutionof Ethyle
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Masayuki Ueta Department of Materials Technology, Faculty of Engineering, Chiba University, Inage-ku, Chiba-shi 263-8522, Japan
Yong Jun Wu Center for Frontier Electronics and Photonics, Chiba University, Inage-ku, Chiba-shi 263-8522, Japan
Kazuyuki Kakegawa Department of Materials Technology, Faculty of Engineering, and Center for Frontier Electronics and Photonics, Chiba University, Inage-ku, Chiba-shi 263-8522, Japan (Received 2 July 2003; accepted 22 December 2003)
Cerium oxide (CeO2) nanoparticles were obtained by heating a polyethylene glycol (PEG) solution of cerium nitrate hydrate [Ce(NO3)3 6H2O] at 383 K for 3 h. When the PEG, whose molecular weight was 20,000, was used for the preparation, the monodispersed CeO2, whose particle size was about 102 nm, was obtained. When the mixture of PEG20,000 and ethylene glycol (EG) was used to prepare the PEG solution of cerium nitrate hydrate, the average particle size increased from 102 nm to 660 nm with an increase in the EG content of the solution. The pore structure in the obtained CeO2 particles also depended on the weight ratio between EG and PEG20,000.
I. INTRODUCTION
Cerium (IV) oxide (CeO2) is an n-type semiconductor and an oxygen ion conductor.1 It has many applications, such as in solid oxide fuel cells and oxygen sensors. Furthermore, the use of CeO2 to shield materials from ultraviolet light has intensively been investigated.2–4 For these applications, regulation of the particle size distribution and the morphology are important issues. Furthermore, the processes by which CeO2 particles are prepared must be as simple as possible. In recent years, several novel methods for preparing CeO2 particles have been reported. A method of synthesizing CeO2 powder by a hydrothermal treatment of cerium hydroxide precipitate has been reported by some researchers.5,6 This method makes it possible to obtain particles whose diameter ranges from 3 nm to 16 nm. Zhitomirsky et al. demonstrated a preparation method of ceria particles using electrochemical deposition.7 The preparation method of CeO2 nanoparticles by adding a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2004.0142 J. Mater. Res., Vol. 19, No. 4, Apr 2004
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hydrazine monohydrate to an aqueous solution of cerium nitrate hydrate at 343 K was also reported.8 Furthermore, a preparation process involving a homogeneous precipitation method with urea was reported. Pickering et al. reported a method for preparing nanocrystalline CeO2 powders with a crystallite size smaller than 5 nm that involved a two-step precipitation.9 They prepared CeO2 particles by oxidizing Ce3+ ion to Ce4+ ion with H2O2 in an aqueous solution, then increasing the pH of the solution. The preparation method using H2O2 produces weakly aggregated CeO2 nanoparticles. Thus, various kinds of methods for the synthesis of CeO2 particles through the solution process have been reported.10 We have reported that polyethylene glycol [PEG HO– (–CH2CH2O
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