Construction of broad-spectrum light absorption inorganic ultra-black coating with multi-scale light-absorbing structures based on hollow CuCr₂O₄spheres

Ultra-black coating can suppress stray light to ensure high-quality imaging of the spacecraft optical instruments. Currently, the mainly used coating is an organic ultra-black coating, which is easy to generate volatile substances at high temperatures, and contaminate the lens, leading to a decline in imaging quality. Therefore, it is urgent to develop a highly stable inorganic ultra-black coating. Herein, we developed all-inorganic coating composed of hollow CuCr₂O₄microspheres (CuCr₂O₄-HS) and potassium silicate resin, which was fabricated through a spraying and self-assembly process. The solar absorptivity and average emissivity of CuCr₂O₄-HS coating (α = 96.26 %, ε = 92.21 %) is superior to that of commercial CuCr₂O₄-B coating (α = 94.43 %, ε = 88.79 %), and it shows a stable wide-angle absorption (up to an incident angle of 70°), which can be attributed to synergistic effects at both the nanoscale and molecular levels: (1) structural absorption resulting from multiple scattering within the CuCr₂O₄HS spherical close-packed arrays; and (2) strong forward scattering and internal multiple scattering by individual hollow spherical particles, as well as intrinsic light absorption due to LOMO–HOMO orbital transitions within the CuCr₂O₄particles. Moreover, the coatings also offer favorable thermal resistance (α = 96.06 %, ε = 92.08 % after exposure to 800 °C for 3 h), making them a promising candidate for ultra-black surfaces in hypersonic vehicles. The work provides a strategy for preparing a highly stable and ultra-black inorganic coating with wide-angle light absorption.