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

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 & AP;1-24 & mu;m. This record high emissivity to thermal conductivity ratio (& AP;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 & DEG;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 & mu;m) and strong phonon-polariton resonances wavelengths (>13 & mu;m) 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 (& AP;11 x 10(-6) K-1 at 1200 & DEG;C) comparable to YSZ, showing great potential in the radiation thermal protection field.