Potential of glassy carbon and silicon carbide photonic structures as electromagnetic radiation shields for atmospheric re-entry

Photonic response and temperature evolution of SiO2/TiO2 multilayers

The microstructural and optical reflectivity response of photonic SiO₂/TiO₂ nanomultilayers have been investigated as a function of temperature and up to the material system's melting point. The nanomultilayers exhibit high, broadband reflectivities up to 1350 °C with values that exceed 75% for a 1 μm broad wavelength range (600-1600 nm). The optimized nanometer sized, dielectric multilayers undergo phase transformations from anatase TiO₂ and amorphous SiO₂ to the thermodynamically stable phases, rutile and cristobalite, respectively, that alter their structural morphology from the initial multilayers to that of a scatterer. Nonetheless, they retain their photonic characteristics, when characterized on top of selected substrate foils. The thermal behavior of the nanometer sized multilayers has been investigated by differential thermal analysis (DTA) and compared to that of commercially available, mm-sized, annealed powders. The same melting reactions were observed, but the temperatures were lower for the nm-sized samples. The samples were characterized using X-ray powder diffraction before DTA and after annealing at temperatures of 1350 and 1700 °C. The microstructural evolution and phase compositions were investigated by scanning electron microscopy and energy-dispersive X-ray spectroscopy measurements. The limited mutual solubility of one material to another, in combination with the preservation of their optical reflectivity response even after annealing, makes them an interesting material system for high-temperature, photonic coatings, such as photovoltaics, aerospace re-entry and gas turbines, where ultra-high temperatures and intense thermal radiation are present.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s10853-021-06557-y.

Broadband, High-Temperature Stable Reflector for Aerospace Thermal Radiation Protection

A simple and thermally stable photonic heterostructure exhibiting high average reflectivity (⟨R⟩ ≈ 88.8%) across a broad wavelength range (920-1450 nm) is presented. The design combines a thin, highly reflective and broadband metallic substrate (Ta) with an optimized dielectric coating (10 layers) to create an enhanced reflector with improved optical and thermal properties compared to its constituents. The heterostructure exhibits temperature-reversible reflective properties up to 1000 °C. In order to take advantage of the high reflectivity and temperature stable properties of this coating, in a wide range of non-photonic composite materials, we have fabricated heterostructure platelets as additives. By impregnating these additives into other types of materials, their response can be photonically enhanced.  Platelets of such a heterostructure have been introduced inside an organic matrix to increase its broadband reflection performance. The platelet-impregnated matrix displays an average reflectivity improvement from 5% to an average of 55% over a 1000 nm range, making it a suitable additive for next generation thermal protection systems (TPS).

A metal-free 3C-SiC/g-C3N4 composite with enhanced visible light photocatalytic activity

Insufficient visible light absorption and fast recombination of the photogenerated electron–hole pairs have seriously hampered the photocatalytic performance of graphitic carbon nitride (g-C₃N₄) up to now.