A Promising Radiation Thermal Protection Coating Based on Lamellar Porous Ca‐Cr co‐Doped Y 3 NbO 7 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: 01.11.2023
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.202305650

Abstract 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 Y 3 NbO 7 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.