La2Hf2O7 Based TBC Materials with Near-Infrared Ultra-Low Transmittance for Thermal Radiation Shielding

As the thrust-weight ratios of aero-engines increase, the severe thermal radiation emitted by high-temperature gases (>= 1800 K) poses a significant challenge for thermal barrier coating (TBC) materials. Traditional TBC materials, despite their reliable thermal insulation properties, are nearly transparent to infrared radiation, which leads to direct radiative heating of the metallic substrate, consequently reducing its service life. In response, a La2Hf2O7-based ceramic doped with a NiFe2O4 second phase is developed to prevent the penetration of thermal radiation and achieve exceptional thermal radiation shielding properties. The experimental results exhibit that 85%La2Hf2O7/15%NiFe2O4 possesses high absorptivity exceeding 0.85 across a broad wavelength range (0.2-14 mu m), and ultra-low transmittance of 0.001 in the range of 0.4-2.5 mu m. It attributes to the presence of multi-valent transition elements (Ni+/Ni2+ and Fe2+/Fe3+) in NiFe2O4, which significantly reduce the band gap width, enhancing photon absorption, scattering, and electron transition probability following infrared radiation absorption. These multifaceted contributions minimize radiative thermal conductivity to 1.55 W m(-1) K-1, effectively shielding the radiative heat transfer. These advantages make this high-temperature thermal shielding strategy highly competitive for the next generation of TBC materials development and application.