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

•High NIR reflecting pigments Co0.5Mg0.5Al2O4 were synthesized by the Pechini-type sol–gel method.•The doping of Fe3 + changed the pigment color from blue to black.•Pigment properties make it a potential candidate for use as cool pigments.

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 °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.

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