Kutty, TRN and Nayak, M (1998) Hydration reactions of nonstoichiometric barium orthoaluminates. In: Cement and Concrete Research, 28 (10). pp. 1363-1404.
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The hydration reactions of the nonstoichiometric barium orthoaluminates having the chemical formula Ba1-xAl2O4-x (0<x<0.56) are studied. On exposure to CO2-free humid air, this compound reacted to form a new hydration product, barium alumino hydroxy hydrate, Ba1-xAl2(OH)(8-2x). yH(2)O, wherein Al3+ is in octahedral coordination, as indicated by Al-27 magic angle spinning nuclear magnetic resonance (MAS NMR). The formation of hydrated product is faster for the nonstoichiometric compositions (x > 0). The collapse of the nepheline-type structure of barium orthoaluminate is explained in terms of the relative migration of Ba2+ ions from the structural channels. Increases in the reaction rate for the nonstoichiometric samples are attributed to faster diffusion of the hydroxyl ions in the lattice, assisted by the structural vacancies. The product is highly sensitive to CO,; on exposure this compound gives rise to barium aluminium carbonato-oxyhydroxide and eventually segregates to BaCO3 and aluminium hydroxide. On heating the hydrated product to 600 degrees C, the compound decomposed to Ba1-xAl2O4-x, indicating the reversibility of the reaction. The reactions involved, microstructural changes, and the possible mechanism of formation of hydrated products are discussed in detail.
|Item Type:||Journal Article|
|Additional Information:||Copyright of this article belongs to Elsevier Science.|
|Department/Centre:||Division of Chemical Sciences > Materials Research Centre|
|Date Deposited:||12 Aug 2009 09:36|
|Last Modified:||19 Sep 2010 05:24|
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