Synthesis and characterization of Fe3+ doped Co0.5Mg0.5Al2O4 inorganic pigments with high near-infrared reflectance

In this work, a series of near-infrared reflective inorganic pigments with a general formula Co0.5Mg0.5Al2-xFexO4 (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) were successfully prepared by Pechini-type sol-gel method. Comprehensive analyses were carried out to characterize the developed pigment powders including thermogravimetry and differential scanning calorimetry, X-ray diffraction, field emission scanning electron microscopy, ultraviolet-visible near infrared diffuse reflectance spectroscopy, and CIE-L*a*b* 1976 color scales. The results demonstrated that the single-phase Co0.5Mg0.5Al2-XFeXO4 was synthesized at an optimum temperature of 900 degrees C. The resulting calcined powders have a well-developed cubic spinel structure. The substitution of Fe3+ for Al3+ in Co0.5Mg0.5Al2-xFexO4 changes the color from blue to black and the band gap shifts from 4.40 eV to 3.50 eV. And Fe doped pigments possess high near-infrared solar reflectance (>43%) in the range of 780-2500 nm. Therefore, these Co0.5Mg0.5Al2-xFexO4 powders have great potential in serving as cool pigments for building coatings. (C) 2016 Elsevier B.V. All rights reserved.