a b s t r a c tSolar selective coatings based on double Al 2 O 3 :W cermet layers and AlSiN/AlSiON bilayer structures were prepared by magnetron sputtering. Both were deposited on stainless steel substrates using a metallic tungsten (W) layer as back reflector. The coating stacks were completed by an antireflection (AR) layer composed of Al 2 O 3 , SiO 2 , or AlSiO x . Spectrophotometer measurements, X-Ray diffraction, Scanning electron microscopy, Energy Dispersive X-Ray Spectroscopy and Rutherford Backscattering Spectrometry were used to characterize the optical properties, crystalline structure, morphology and composition of these coatings. The spectral optical constants of the single layers were calculated from the reflectance and transmittance measurements and used to design the optical stack. The coatings exhibit a solar absorptance of 93-95% and an emissivity of 7-10% (at 400 1C). The coatings also exhibit excellent thermal stability, with small changes in the optical properties of the coating during heattreatments at 400 1C in air for 2500 h and at 580 1C in vacuum for 850 h. The coating based on the AlSiN/ AlSiON bilayer structure was obtained with an Al:Si ratio of 2.5:1. These coatings revealed similar performance as the one obtained with coatings based on Al 2 O 3 :W cermet layers.
Characterization of a TiAlN/TiAlON/SiO 2 tandem absorber is reported in this contribution. The first two layers were deposited by magnetron sputtering and the third layer was prepared by plasma enhanced chemical vapour deposition (PECVD). The optimization was performed by determining the optical constants of individual layers by first measuring spectral transmittance and reflectance of the individual layers. Subsequently the measuring spectra were fitted using the SCOUT software and dielectric function of each layer was determined. The three layer stack absorber on copper was then designed using those optical properties. The thickness of the individual layers was optimized until a solar absorptance of 95.5% was obtained resulting in a total thickness of about 215 nm (65 nm/51 nm/100 nm for the individual layers, respectively). A thermal emittance of 5% for an absorber temperature of 100°C was obtained by analyzing the measuring data from a FTIR spectrometer with integrating sphere. During continuous thermal annealing at 278°C for 600 h the absorptance decreased by 0.4%.
This study presents a design of multilayer solar selective absorber for high temperature applications. The optical stack of this absorber is composed of four layers deposited by magnetron sputtering on stainless steel substrates. The first is a back-reflector tungsten layer, which is followed by two absorption layers based on CrAlSiN x / CrAlSiO y N x structure for phase interference. The final layer is an antireflection layer of SiAlO x. The design was theoretically modelled with SCOUT software using transmittance and reflectance curves of individual thin layers, which were deposited on glass substrates. The final design shows simultaneously high solar absorbance α= 95.2 % and low emissivity ε= 9.8% (at 400 ºC) together with high thermal stability at 400 ºC, in air, and 600 ºC in vacuum for 650 h.
Preparation and characterization of TiAlSiN/TiAlSiON/SiO 2 solar selective absorber is reported in this contribution. All layers were deposited in a continuous mode using a industrial equipment, the nitride and oxynitride were prepared by reactive magnetron sputtering and the SiO 2 layer by Plasma Enhanced Chemical Vapor Deposition. The optical constants of individual layers were calculated by modelling of spectral transmittance and reflectance of the individual layers. The three layer stack absorber was then designed using those optical properties. The thickness of the individual layers was optimized until a solar absorptance of 96% was obtained resulting in a total thickness of about 200 nm, deposited in copper and extruded aluminium absorbers. A thermal emittance of 5 % for an absorber temperature of 100 ºC was obtained by analyzing the measuring data from a FTIR spectrometer with integrating sphere. After test duration of 600 h, the samples subjected to a thermal annealing at 278 ºC in air showed a performance criterion (PC) below 4% for, while the samples in the humidity tests showed a PC below 2 %,
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