A Promising Radiation Thermal Protection Coating Based on Lamellar Porous Ca‐Cr co‐Doped Y3NbO7 Ceramic

• Published in: Advanced functional materials Vol. 33; no. 47
• Main Authors: Chen, Guoliang, Fu, Haoyang, Zou, Yongchun, Wang, Shuqi, Gao, Yongwang, Yue, Tongtong, Cao, Jianyun, Wang, Yaming, Qiu, Jun, Zhao, Junming, Ouyang, Jiahu, Jia, Dechang, Shuai, Yong, Zhou, Yu
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc 16.11.2023
• Subjects: Bonding strength; Coating; Conduction heating; Conductive heat transfer; Emissivity; Heat conductivity; lamellar porous structures; Lamellar structure; Materials science; Polaritons; Radiation; radiative thermal protection; Refractivity; Resonance scattering; Thermal conductivity; Thermal expansion; Thermal protection; thermal spraying coatings; Thermal stability; Wavelengths; Yttria-stabilized zirconia
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.202305650

Dissipation of heat efficiently from a hot object via radiation while minimizing the inward heat conduction is the key requirement of radiation thermal protection. In this study, a Ca‐Cr co‐doped Y3NbO7 coating with lamellar porous structure is fabricated, which shows an ultra‐low thermal conductivity (<0.7 W m−1 K−1) and near‐unity emissivity (>0.9) across a broad wavelength range of ≈1–24 µm. This record high emissivity to thermal conductivity ratio (≈1.3) is experimentally and theoretically revealed from a multi‐scale perspective. The diffusoin‐mediated thermal conduction feature of niobates combined with lamellar porous structure of the coating reduces its thermal conductivity to an impressive 0.5 W m−1 K−1 at 25 °C, surpassing the theoretical amorphous limitation of 0.72 W m−1 K−1. Experiments and FDTD calculation results demonstrate that the intrinsic emissivity dips at shallow extinction wavelengths (1 and 8 µm) and strong phonon‐polariton resonances wavelengths (>13 µm) can be effectively compensated by the multiple scattering/absorption and gradual modulation of conical shape/effective refractive index induced by surface micro‐protrusion structures, respectively. Furthermore, the coating exhibits robust mechanical and thermal stability with a high bonding strength (18.3 MPa) and thermal expansion coefficient (≈11 × 10−6 K−1 at 1200 °C) comparable to YSZ, showing great potential in the radiation thermal protection field. A niobate‐based coating is designed and synthesized with great radiation thermal protection properties via its record high emissivity to thermal conductivity ratio (ε/κ). The lamellar porous structure reduces the thermal conductivity to an impressive 0.5 W m−1 K−1. The surface micro‐protrusion can effectively compensate the intrinsic emissivity dips at shallow extinction or strong phonon‐polariton resonances wavelengths.