Improvement of near-infrared (NIR) reflectivity and black color tone by doping Zn(2+) into the Ca(2)Mn(0.85)Ti(0.15)O(4) structure

Inorganic black pigments with thermal barrier characteristics, Ca(2)Mn(0.85−x)Ti(0.15)Zn(x)O(4−x) (0 ≤ x ≤ 0.10), were synthesized using a conventional solid-state reaction method in order to improve the blackness without decreasing the near-infrared (NIR) reflectance of a Ca(2)Mn(0.85)Ti(0.15)O(4) pigment, which was previously reported by our group. The composition was optimized to provide both high blackness and NIR reflection characteristics. As a result, the NIR solar reflectance value (R(NIR)) of Ca(2)Mn(0.77)Ti(0.15)Zn(0.08)O(3.92) (R(NIR) = 74.6%) became larger than that of Ca(2)Mn(0.85)Ti(0.15)O(4) (R(NIR) = 71.7%), and the black color tone of the former (L* = 23.2, a* = +2.81, b* = +0.83, C = 2.93) was improved in comparison with that of the latter (L* = 24.4, a* = +4.30, b* = +2.72, C = 5.09). This improvement is caused by the introduction of strain into the [MnO(6)] octahedra and a decrease in the manganese ion concentration. The R(NIR) value of the Ca(2)Mn(0.77)Ti(0.15)Zn(0.08)O(3.92) pigment was also larger than those of the commercially available pigments (R(NIR) < 53.0%). Therefore, Ca(2)Mn(0.77)Ti(0.15)Zn(0.08)O(3.92) has potential to be an inorganic black pigment for thermal shielding.