Synthesis of NIR-Reflective Oxide Ceramic Orange Pigment from MgO and Leucoxene

A series of NIR-reflective brownish orange pigments comprising various amounts of Fe2O3 have been synthesized by a conventional solid-state reaction at 1100 degrees C. Magnesium titanate base pigment was synthesized from MgO and leucoxene mineral which was employed as TiO2 source. The resultant pigment had brownish gray appearance (L*a*b* = 68.67, 7.83, 18.68, respectively) and NIR reflectance of 81.0%. Incorporating the magnesium titanate pigment with various amounts of Fe2O3 (molar ratio (x) = 0.1, 0.3, 0.5, 0.7, 0.9 and 1.0) resulted in a change of color hue to brownish orange, and a change of NIR reflectance from 81.0 to 41.1% upon the increase of Fe2O3 content. Optical bang-gap energies derived from diffused reflectance spectra reduced from 2.75 eV for the magnesium titanate to 2.25, 2.20, 2.10, 1.90, 1.70 and 1.60 eV for pigments incorporated with 0.1, 0.3, 0.5, 0.7, 0.9 and 1.0 mole Fe2O3, respectively. At the optimum synthesis condition (x = 0.3), the pigment exhibited light brownish orange color hue (L*a*b* = 52.02, 23.94, 39.37) and NIR reflectance of 80.1%. An accelerated QUV weathering test according to the ASTM G154-16 standard revealed color fading (Delta E*) of only 0.95 indicating excellent weathering stability.