Fabrication of 12CaO 7Al2O3 powders with high specific surface area by sol-gel and ball-milling method

Abstract

12CaO·7Al2O3 (called as C12A7) is composed of [Ca24Al28O64]4+ cages in which oxide anions are entrapped. Recent studies have revealed that the outstanding characteristics appear by exchanging the free oxide anions in the cages by various other anion species. In the present report, in order to enhance the oxidative catalytic activity of C12A7 by the encaged oxygen radicals, we synthesized C12A7 fine powders with high-specific surface area by sol–gel method and subsequent ball-milling. Aluminum sec-butoxide, calcium nitrate tetrahydrate, absolute ethanol, 1 M hydrochloric acid, and ethyl 3-oxobutanate were used as raw materials. The obtained precursor solution was dried at 100°C for 24 h, and the product obtained was annealed at 900°C in O2 atmosphere. Planetary ball milling was subsequently applied to the C12A7 powders. The XRD measurements revealed that the synthesized sample was a single phase C12A7. The BET specific surface area of the ground samples was 48.9 m2/g (24 h ground) and 17.3 m2/g (36 h ground) for those prepared by sol–gel method and by solid state reaction, respectively. The possibility was thus demonstrated on the synthesis of C12A7 fine powders with higher specific surface area by sol–gel method and subsequent planetary ball-milling.