Synthesis of Nanoscale Nd-Doped Ceria Via Urea-Formaldehyde Combustion Method
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BECAUSE of the isotropic structure, cerium oxide is a transparent ceramic suitable for applications in different optical and optoelectronic devices.[1] It can withstand high temperatures and harsh conditions during processing without losing its optical properties.[2] The material has found many other potential applications in some fields such as gas sensors,[3] absorbents of electromagnetic wave in ultraviolet range,[4] electrolyte and anode materials in solid oxide fuel cells,[5] and oxidation-resistant coatings for high-temperature application.[6] The nanocrystalline materials display a quantum confinement effect evidenced through blue shift in the ultraviolet absorption spectrum,[4] lattice expansion,[7] and shifting and broadening in Raman allowed modes.[8] Recently, the material has also become a potential candidate in the field of catalytic bed, specifically due to its oxygen absorption and release capabilities.[9] These capabilities result from the ability of cerium to change valance state from 4+ to 3+, while existing large octahedral void allows the oxygen movement inside the structure.[10,11] In addition to these intrinsic properties, the oxygen absorption and desorption characteristics can be maneuvered extrinsically through (1) the addition of lower valent cations into the sites of Ce4+ and thereby (2) the simultaneous creation of oxygen vacancy in structure to maintain charge neutrality. Investigations with rareearth oxides are available in this regard.[12–14] Nanocrystalline powders have been prepared by various routes such as the conventional solid-state reaction method,[15] M. BISWAS, Research Associate, and S. BANDYOPADHYAY, Chief Scientist, are with the CSIR-Central Glass & Ceramic Research Institute, Kolkata 700 032, India. Contact e-mail: [email protected] Manuscript submitted October 9, 2012. METALLURGICAL AND MATERIALS TRANSACTIONS A
carbonate coprecipitation,[16] oxalate coprecipitation,[17] self-propagating room-temperature synthesis,[18] microemulsion process,[13] etc. The gel combustion route can be regarded as another attractive alternative for nanosized material preparation.[19] The attractive feature of this process lies in an intimate blending among the fuel or complexing agents (e.g., glycine, citric acid, urea, L-alanine, etc.) and oxidizer in an aqueous medium. [20–23] The mixture gets ignited with subsequent selfsustaining exothermic redox reaction between the fuel and the oxidant. The rapid evolution of a large volume of gases due to the exothermic (combustion) reaction dissipates the heat of combustion, thereby limiting the increase of temperature that, in turn, reduces the possibility of local partial sintering among the primary particles. In this synthesis route, the type and amount of fuel play significant role in determining particle morphology. Urea formaldehyde (UF) as fuel has shown interesting results in synthesizing nanocrystalline yttria -doped ceria[24] and lanthanum strontium manganate powders.[25] In the current work, the possibility of preparing nanocrystalline c
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