| Affiliation: | 1. School of Energy Science and Engineering, Key Laboratory of Aerospace Thermophysics, Ministry of Industry and Information Technology, Harbin Institute of Technology, Harbin, 150001 China Institute for Advanced Ceramics, Key Laboratory of Advanced Structure-Function Integrated Materials and Green Manufacturing Technology, Harbin Institute of Technology, Harbin, 150080 China;2. State Key Laboratory for Pollution Control and Resource Reuse, College of Environmental Science and Engineering, Tongji University, Shanghai, 200092 China;3. Institute for Advanced Ceramics, Key Laboratory of Advanced Structure-Function Integrated Materials and Green Manufacturing Technology, Harbin Institute of Technology, Harbin, 150080 China;4. School of Energy Science and Engineering, Key Laboratory of Aerospace Thermophysics, Ministry of Industry and Information Technology, Harbin Institute of Technology, Harbin, 150001 China;5. Key Laboratory of LCR Materials and Devices of Yunnan Province, School of Materials Science and Energy, Yunnan University, Kunming, 650500 China |
| 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 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. |
