Abstract
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.
Highlights
High-temperature photonic materials are attracting more and more attention for applications where thermal stability and optical response as a function of temperature are critical parameters
The high-temperature characteristics of SiO2/TiO2 nanomultilayers demonstrated that the materials are interesting as a photonic additives for generation photonically enhanced thermal protection systems (TPS)
It has been shown that a powder of SiO2/ TiO2 nanomultilayers has increased the diffuse reflectivity of the underlying substrate base to values exceeding 75% across the whole VIS and part of the NIR electromagnetic spectrum
Summary
High-temperature photonic materials are attracting more and more attention for applications where thermal stability and optical response as a function of temperature are critical parameters. 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. We investigate the high-temperature microstructure evolution and photonic behavior of nanomultilayer SiO2/TiO2 samples up to 1710 °C.
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