Synthesis and characterization of blue TiO2/CoAl2O4 complex pigments with good colour and enhanced near-infrared reflectance properties

Abstract

Blue TiO₂/CoAl₂O₄ complex pigments were prepared through calcination of precursors from the precipitation of Al³⁺ and Co²⁺ on TiO₂ particles in sequence. The synthesized powders were characterized by colorimetry, near-infrared diffuse reflectance spectroscopy, X-ray diffraction, scanning electron microscopy and ultraviolet-visible spectroscopy. The pigments were found to have composite phases composed of rutile TiO₂ and spinel CoAl₂O₄. The bright blue pigments having good color properties could be obtained via calcination of the precursors at 1000 °C. As the mass of CoAl₂O₄ increased to 40 wt% of TiO₂, the pigments presented good color properties (L* = 53.43, a* = −4.75, b* = −41.78) and the results showed little variation with an increase in the CoAl₂O₄ content. In comparison to the pure CoAl₂O₄ pigments, the as-prepared pigments with a CoAl₂O₄/TiO₂ mass ratio of 0.4 exhibited an enhanced near-infrared reflectance and also showed better color properties relative to the mixed pigments of TiO₂ and CoAl₂O₄.