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Preparation of 3CaO.Aal2O3 and 12CaO.7Al2O3 by a precursor method

I. Nerád

Institute of Inorganic Chemistry, Centre for Chemical Research, Slovak Academy of Sciences, CS-84236 Bratislava

 

Abstract: Calcium aluminates ЗСаО-Al203 and 12CaO-7Al203 were synthesized by thermal treatment of precursors prepared from aluminium nitrate, calcium nitrate, and tartaric acid. 1 M store aqueous solutions of Al(N03)3 and Ca(N03)2 were prepared by dissolution of metallic aluminium and CaC03, respectively, in diluted nitric acid. After mixing these solutions at the stoichiometric ratio corresponding to the synthesized calcium aluminate tartaric acid (2 mol) for each mole of metal was added. On heating this solution at atmospheric pressure a solid precursor was obtained. It con­tained an organic component which was removed by calcinating the sample for 2 to 6 h in open atmosphere at the temperature of 950 °C. The synthesis of ЗСаО • Al203 and 12CaO • 7Al203 was finished after 4 h and 3 h heating of the intermediate products. The intermediate product contained no organ­ic substances and the ratio of amounts of substances was л(СаО):n(Аl203) = 3:1 and n(СаО):n(Аl203) = 12:7, respectively, at the tem­perature of 1300 °C. In both cases firstly CaO and Al203 react in a reduction atmosphere caused by combustion of the organic component of precursor under formation of an orthorhombic phase 5CaO • 3Al203. In the case of the sample with the ratio n(СаО):n(Аl203) = 3:1 5CaO-3Al203 reacts with CaO directly under formation of ЗСаО • Al203 without forming 12CaO • 7Al203 as an intermediate product. In the case of the sample with the ratio n(CaO): n(Аl203) = 12 : 7 5CaO • 3Al203 reacts under the influence of oxy gen and/or water vapour and 12CaO • 7Al203 is formed.

Full paper in Portable Document Format: 416a723.pdf

 

Chemical Papers 41 (6) 723–729 (1987)

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