Preparation of Cr2O3-based pigments with high NIR reflectance via thermal decomposition of CrOOH

Abstract In order to reduce greenhouse gas emission and urban heat island mitigation, pure and titanium(Ti)-doped Cr 2 O 3 cool pigments were prepared via the thermal decomposition of CrOOH. The result reveals that the pure Cr 2 O 3 pigment presents both a high near-infrared reflectance and excellent yellowish-green color. Meanwhile, titanium was doped to improve the NIR reflectance and strengthen the color. The color of the designed pigments was brighter, and most importantly, the NIR reflectance increased from 84.04% to 91.25% with increasing Ti content from 0 to 0.006% (mole fraction). However, excessive doping of Ti 4+ for Cr 3+ in Cr 2 O 3 ( x (Ti)≤0.008%) decreased the NIR reflectance. One possible reason is that the conductivity type of the Cr 2− x Ti x O 3+ δ changed from p-type conduction to n-type conduction with increasing Ti content, accompanied by the change of the electrical resistivity and the NIR reflectance. The prepared yellowish-green Cr 2 O 3 pigments have a great potential for extensive applications in construction and military.