A novel high NIR-reflective cobalt- and nickel-free black pigment Na2Mn3O7: Synthesis, characterization, and chromaticity properties

Black pigments faced strict limits due to the heavy metal toxicity (Co, Ni), limited resources, and high costs. This study report for the first time the application of a new Co- and Ni-free Na 2 Mn 3 O 7 as a ceramic black pigment with high near-infrared (NIR) reflectance. XRD, FE-SEM, EDS-Mapping, UV-V is , TEM, and CIELAB colorimetry were used to study its properties. The FE-SEM results show the product has irregular flake-like particles, proving layered structure nature of Na 2 Mn 3 O 7 . The color values of the black pigment are L∗ = 17.27, a∗ = −0.05, and b∗ = −1.25. Remarkedly, its L∗ value is lower than that of commercial carbon black, and other currently reported black pigments. The chromatic mechanism originates from the combined effects of Mn 4+ d-d electronic transitions and Mn 4+ →O 2− charge transfer transitions, which together result in broad absorption across the visible region and a pure black color. The glaze shows a shiny black color when applied the pigment as ceramic glazes at 1200 °C in air, and the color values are L∗ = 25.31, a∗ = −2.56, and b∗ = 0.11. Notably, the glaze after high-temperature achieves a near-infrared reflectance of 36.2%, which is only slightly lower than the 45% reflectance of the commercial black near-infrared pigment (Black L 0095). This research provides useful guidance for developing black pigments without Co and Ni.