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2590260 
Journal Article 
Bright blue pigment CoAl2O4 nanocrystals prepared by modified sol-gel method 
Salavati-Niasari, M; Farhadi-Khouzani, M; Davar, F 
2009 
Yes 
Journal of Sol-Gel Science and Technology
ISSN: 0928-0707
EISSN: 1573-4846 
52 
321-327 
Bright blue ceramic CoAl2O4 nanocrystals was prepared by sol-gel technique using aluminum nitrate, cobalt nitrates, diethylene glycol monoethyl ether, and citric acid were used as precursor materials. This method starts from of the precursor complex, and involves formation of homogeneous solid intermediates, reducing atomic diffusion processes during thermal treatment. The formation of pure crystallized CoAl2O4 nanocrystals occurred when the precursor was heat-treated at 350 A degrees C in air for 2 h. The stages of the formation of CoAl2O4, as well as the characterization of the resulting compounds were done using thermo-gravimetric analysis, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The structure, coloration, particle size, and temperature of formation of the resulting CoAl2O4 phases were found to depend on the precursors and methods used for preparation and the calcination temperature. The UV-vis spectra presented three bands at 538,575 and 617 nm attributed to the Co2+ spin transitions in tetrahedral sites. UV-vis spectroscopy of the samples allows to compare the band shift with the size variation. These results improve that the bright blue nanopigment was obtained at the presence of citric acid as capping agent. The lowest temperature for preparation of the blue cobalt aluminate is about 400 A degrees C. This temperature is much lower than that needed for preparation of the compound through traditional solid-state reactions (above 1,000 A degrees C). 
Powders-chemical preparation; CoAl2O4; Nanopigment; Sol-gel; Transition metal oxides 
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• Cobalt
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