Blue CoAl₂O₄ Particles Prepared by the Sol−Gel and Citrate−Gel Methods

Abstract

Bright blue CoAl2O4 particles were prepared by the sol−gel and citrate−gel methods using aluminum sec-butoxide, cobalt salts, and citric acid as oxides precursors. Both methods start from sols of the precursor alkoxides and salts, and involve formation of homogeneous solid intermediates, reducing atomic diffusion processes during thermal treatment. This important feature results in a substantial lowering of the time and temperature needed for the formation of the desired compounds. The stages of the formation of CoAl2O4, as well as the characterization of the resulting compounds were done using XRD, FTIR, UV−VIS, SEM, and TGA/DTA techniques. The structure, coloration, particle size, and temperature of formation of the resulting CoAl2O4 phases were found to depend on the precursors and methods used for preparation and the calcination temperature. The lowest temperature for preparation of the blue cobalt aluminate of about 700 °C was obtained using the citrate−gel method. This temperature is much lower than that needed for preparation of the compound through traditional solid-state reactions (above 1000 °C).