Synthesis of C12A7 calcium aluminate aerogels

Abstract

Calcium aluminate aerogels with mayenite stoichiometry C12A7 were prepared for the first time. The surface area of amorphous aerogel obtained after hydrolysis with stoichiometric amount of water was about 330 m2/g after the supercritical drying and 170 m2/g after calcination at 500 °C. The latter sample mostly consisted of 10–20 nm amorphous platelets. The mayenite phase was observed after the supercritical drying only if overstoichiometric amount of water was used for hydrolysis. Diphenyloxyl nitroxyl radicals were observed on the surface of calcined C12A7 aerogels after diphenylamine adsorption. Their formation on the surface of the samples calcined at 500 °C suggests that mayenite cages capable of stabilizing active forms of oxygen are present on the surface of the amorphous aerogels.