Sol-gel combustion synthesis and characterization of CoCr 2 O 4 ceramic powder used as color solar absorber pigment

A facile citric acid assisted sol-gel combustion method was performed to synthesize cobalt chromite (CoCr 2 O 4 ) ceramic pigment. The effect of the annealing temperature on structure, morphologies, and optical properties of the prepared CoCr 2 O 4 pigments were systematically studied by thermogravimetry, differential thermal analysis, X-ray diffraction (XRD) and field emission scanning electron microscope (FESEM). The results show that CoCr 2 O 4 spinel crystal was achieved after heat treatment of the as-burnt powder at a relatively low temperature (400 °C) and the average crystallite size of the CoCr 2 O 4 pigment increased with the annealing temperature. Furthermore, on the CIE parameters of CoCr 2 O 4 pigment, a * and b * values became much more negative with the annealing temperature due to much more Co 2+ ions located in tetrahedral sites and much more Cr 3+ ions located in octahedral sites. Finally, the measured solar absorptance indicates that this ceramic pigment is expected to fabricate the color paint coating for solar absorber application.