New red pigments based on Li3AlMnO5 for NIR reflective cool coatings

Abstract

The exploration of new red pigments based on transition elements is of great practical value in the field of inorganic pigments, since the red coloured pigments have unique applications in paints, ceramic tiles, cosmetics, etc. Here we mainly reported a new class of eco-friendly red pigments based on substituted Li3AlMnO5 (LAMO) and briefly state about the other rock salt layered structure Li3GaMnO5 (LGMO). The solid-state synthesized powders were crystallized to monoclinic structure having MnIV(1)2b and MnIV(2)4g site. The absorption bands in the synthesized samples mainly arises due to the octahedrally coordinated MnIVO6 in the 4g site. Among the synthesized samples, LAMO: 0.10Ti4+ showed exemplary chromatic properties. The doping of tetravalent Ti4+ ions in the Mn4+ sites altered the MnIV(2)O6 bond lengths and increased the crystal field around the absorption band attributed to the 4A2g→4T2g transitions. The ball milled LAMO: 0.10Ti4+shows the a* value of 40.05, which is higher than that of the commercially available red iron oxide pigments (a* = 28.9). Meanwhile, the brighter red powder LAMO: 0.10Ti4+ demonstrated appreciable thermal and chemical stability. From the thermal evaluating study, we observed that, LAMO: 0.10Ti4+ pigment coated roof panels showed a temperature difference of (3.2 °C) compared to the bare roof panel (3.7 °C). We estimated the coating's performance of the LAMO: 0.10Ti4+ in concrete block, metal plate and ceramic tile. In these substrates, the pigment possesses distinctly elevated NIR‐reflectance, which makes these materials worthwhile for cool coating applications.