ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

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)