| Summary: | 碩士 === 國立虎尾科技大學 === 材料科學與工程系材料科學與綠色能源工程碩士班 === 107 === In order to reduce environment pollution, various renewable energies such as biomass energy, geothermal energy, tidal energy, hydro-electric power, wind energy, and solar energy, have been used. The solar photo-thermal system is one main application of solar energy. The solar selective absorber plays an important role in solar thermal system. The colored solar selective absorbers can increase the diversity and application of solar photo-thermal system.
In this study, a multi-layer spectrally selective absorber films were deposited by reactive magnetron sputtering. The structure of CrAlN/Cr2O3/Al2O3 absorbers were deposited on Cu substrates. The effect of thickness of Cr2O3 and Al2O3 on the optical properties and colors of absorbers were be studied.
The structure of the studied films was characterized by Field Emission Scanning Electron Microscopy(FE-SEM) and Grazing Incident X-Ray Diffraction(GIXRD). The chemical composition of the coatings was measured by Energy Dispersive Spectrometer(EDS). The refractive indexes and extinction coefficient of CrAlN, Cr2O3 and Al2O3 films were obtained by ellipsometer. The coatings of solar absorbance(α) and thermal emittance(ε) were calculated from the data of measured relative reflectance obtained by UV/VIS/NIR Spectrophotometer and a Fourier Transform Infrared Spectroscopy(FTIR).
Experimental results show that the solar selective absorbing coatings with multilayer structure can display different colors by changing the layer thickness. We adjusted the thickness of the Cr2O3 layer (80 nm, 100 nm and 120 nm) and the Al2O3 layer (50 nm,70 nm and 90 nm). The color of the samples contains yellow, greenish-blue, blue, lightsea-green and purple. This can be further demonstrated by the CIE chromaticity diagram. In this work, the solar absorbance of these absorbers was between 0.86 and 0.95, the thermal emittance was between 0.17 and 0.19.
The thermal stability of the absorbing coatings is studied by annealing for 2 hours at high temperature in vacuum and in air. The optical properties were used to characterize properties of the coatings. The results showed that absorbing coatings were thermally stable at 300 ℃ in air and 500 ℃ in vacuum.
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