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Title of Journal: J SolGel Sci Technol

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Abbravation: Journal of Sol-Gel Science and Technology

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Springer US

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DOI

10.1016/0041-008x(83)90272-7

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1573-4846

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A spectroscopic study of calcium aluminate gels ob

Authors: S Kurajica G Mali T Gazivoda J Sipusic V Mandic
Publish Date: 2009/02/05
Volume: 50, Issue: 1, Pages: 58-68
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Abstract

Calcium aluminate CaAl2O4 CA powders were prepared by sol–gel technique at low sintering temperatures Aluminiumsecbutoxide AlOsBu3 Asb and calcium nitrate tetrahydrate CaNO32 × 4H2O were used as starting materials Ethyl acetoacetate C6H10O3 Eaa was used as a chelating agent in order to control the rate of hydrolysis of AlOsBu3 Three gels with Eaa/Asb molar ratios of 1/1 3/2 and 2/1 were prepared The dried gels and thermally treated samples were characterized by means of Fourier Transform Infrared spectroscopy FTIR 1H 13C Nuclear Magnetic Resonance NMR spectroscopy solidstate 27Al Magic Angle Spinning MAS NMR 3Q MAS NMR spectroscopy and XRay Diffraction XRD From the results obtained the effect of modification of the starting Asb on the hydrolysis process hydrolyzed gel structure and crystallization behavior is discussed It has been established that Eaa reacts completely with Asb forming chelate Various chelate units are formed including trichelated AlEaa3 units Spontaneous gellation has been observed in the sols slowly hydrolyzed by exposing to air moisture The reactivity towards hydrolysis of chelated alkoxide depends on the number of chelating ligands bonded to aluminium Secbutoxy groups were primarily hydrolyzed ethyl acetoacetate groups in less chelated units are much less susceptible to hydrolysis while trichelated units were not hydrolyzed Thus in hydrolyzed gels a partially chelated oligomers and trichelated AlEaa3 units exist The crystal phase not described previously related to AlEaa3 chelate crystallizes in the gels with higher Eaa/Asb ratio Hydrolysis leads to formation of three kinds of Al coordination sites six coordinated AlEaa3 and five and six coordinated Al atoms in oligomers The Eaa/Asb ratio strongly influences the relative ratios between the various coordination states of aluminium atom After thermal treatment of the gels at 1000 °C for 2 h CA was obtained along with minor CaAl4O7 CA2 and Ca12Al14O33C12A7 compounds Thermal treatment at higher temperature increases the amount of CA and decreases the amount of minor componentsThe financial support of the Ministry of Science Education and Sports of Republic of Croatia within the framework of the project No 12512529702981 “Ceramic nanocomposites obtained by sol–gel process” is gratefully acknowledged The authors would like to thank Dr E Mestrovic and I Bratos Pliva dd Zagreb Croatia for performing an MS measurement

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