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Thermal Evolution of Calcium Aluminate Gel
S. Kurajica, V. Mandic, J. Sipusic
University of Zagreb, Faculty of Chemical Engineering and Technology, 19 Marulicev trg, Zagreb, Croatia
received May 25, 2010, received in revised form July 6, 2010, accepted September 23, 2010
Vol. 2, No. 1, Pages 15-22 DOI: 10.4416/JCST2010-00017
Abstract
Calcium aluminate (CaAl2O4) powder was prepared with a sol-gel technique using calcium nitrate tetrahydrate and aluminium sec-butoxide as precursors and ethyl acetoacetate as chelating agent. The dried gel and thermally treated samples were characterized by means of simultaneous Differential Thermal and Thermo-Gravimetric Analysis (DTA/TGA), Fourier Transform Infrared spectroscopy (FTIR), and X-Ray Diffraction (XRD). From the results obtained, the thermal evolution of the prepared gel, the crystallization behaviour and crystallization kinetics are discussed. It has been established that the decomposition of the chelate and the evaporation of ethyl acetoacetate followed by an auto-combustion process occur in a lower temperature range. The crystallization process starts at temperatures higher than 900 °C. Calcium aluminate, CaAl2O4, appears as the major crystalline phase, and calcium dialuminate, CaAl4O7, and dodecacalcium heptaaluminate, Ca12Al14O33, as minor phases. The crystallization processes of the phases proceed simultaneously and independently. Thermal treatment at higher temperature increases the amount of calcium aluminate and decreases the amount of minor components.
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Keywords
Calcium aluminate, sol-gel, thermal evolution, crystallization, non-isothermal kinetics.
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© 2010 Göller Verlag
Acknowledgments
The financial support of the Ministry of Science, Education and Sports of Republic of Croatia within the framework of the project No. 125-1252970-2981 "Ceramic nanocomposites obtained by sol-gel process" is gratefully acknowledged. The authors are much obliged to Prof. J. Macan for the fruitful discussion.
