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

Abstract

A series of NIR-reflective brownish orange pigments comprising various amounts of Fe₂O₃ have been synthesized by a conventional solid-state reaction at 1100 °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 (ΔE*) of only 0.95 indicating excellent weathering stability.

Keywords:

• Magnesium titanate
• NIR-reflective pigment
• cool pigment
• orange pigment
• solid-state reaction

Additional information

Funding

This work was partially supported by the National Metal and Materials Technology Center, the National Science and Technology Development Agency (NSTDA) (Thailand), Grant No. MT-B-61-CER-07-314-I.