Synthesis of Mg1−xCoxAl2O4 blue pigments via combustion route

MgAl2O4 was successfully used as crystalline host network for the synthesis of cobalt-based blue ceramic pigments. Different compositions of Mg1−xCoxAl2O4 (x = 0.1–0.3) powders have been prepared by the combustion reaction of corresponding metal nitrates with mixtures of urea and β-alanine. The resultant powders were characterized by means of XRD, TG-DTA, EDAX, SEM, BET surface area, diffuse reflectance spectrometry and CIEL∗a∗b∗ color measurement. For x = 0.2, thermal analysis investigations evidenced that combustion reaction occurs at 276 °C. XRD analysis certified the formation of the designed solid solution, no additional thermal treatment being required. EDAX elemental analysis confirmed the purity of the as-prepared compound. The resulted powders had large surface areas, which varied from 8.7 to 62.6 m2/g. The crystallite size of Mg1−xCoxAl2O4 powders was less than 15 nm. Experimental results evidenced that as the proportion of Co2+ increased, the crystallite size decreased and the specific surface area increased. The diffuse reflectance spectra of the Mg1−xCoxAl2O4 pigments confirmed the presence of tetrahedrally coordinated Co2+. CIEL∗a∗b∗ chromatic coordinates indicated that the bluest color was obtained for x = 0.2.