Optical and structural analysis of solar selective absorbing coatings based on AlSiOx:W cermets. (1st July 2017)

• Record Type: Journal Article
• Authors: Dias, D.; Rebouta, L.; Costa, P.; Al-Rjoub, A.; Benelmeki, M.; Tavares, C.J.; Barradas, N.P.; Alves, E.; Santilli, P.; Pischow, K.
• Is Part Of: Solar energy. Volume 150(2017)
• Page Start: 335
• Page End: 344
• Publication Date: 2017-07-01
• Subjects: Solar selective absorber -- AlSiOx:W cermet -- Optical constants -- Dielectric function modelling -- Sputtering, solar thermal; Solar energy -- Periodicals; Solar engines -- Periodicals; 621.47
• DOI: 10.1016/j.solener.2017.04.055
• Languages: English
• ISSNs: 0038-092X

Abstract

Graphical abstract: Highlights: W/AlSiOx :W(HA)/AlSiOx :W(LA)/AlSiOx tandem absorber for solar selective absorption. In the HA layer, one third of W atoms are in the W 0 oxidation state. Solar absorbance of 95% and thermal emittance of 11% (at 400 °C). Excellent thermal stability of the coating after 1000 h at 580 °C in vacuum. Abstract: It is reported in this work the development and study of the optical and structural properties of a solar selective absorber cermet based on AlSiOx :W. A four-layer composite film structure, W/AlSiOx :W(HA)/AlSiOx :W(LA)/AlSiOx, was deposited on stainless steel substrates using the magnetron sputtering deposition method. Numerical calculations were performed to simulate the spectral properties of multilayer stacks with varying metal volume fraction cermets and film thickness. The chemical analysis was performed using X-ray photoelectron spectroscopy and the results show that in the high metal volume fraction cermet layer, AlSiOx :W(HA), about one third of W atoms are in the W 0 oxidation state, another third in the W x+ oxidation state and the last third in the W 4+, W 5+ and W 6+ oxidation states. The X-ray diffractograms of AlSiOx :W layers show a broad peak indicating that both, W and AlSiOx, are amorphous. These results indicate that this film structure has a good spectral selective property that is suitable for solar thermal applications, with the coatings exhibiting a solar absorptance of 94–95.5% and emissivities of 8–9% (at 100 °C) and 10–14% (at 400 °C). The samples were subjected to a thermal annealing at 450 °C, in air, and 580 °C, in vacuum and showed very good oxidation resistance and thermal stability. Morphological characterizations were carried out using scanning electron microscopy and atomic force microscopy. Rutherford Backscattering experiments were also performed to analyze the tungsten depth profile.