Spray-pyrolyzed Al2O3-Ag Nano-Cermets coatings for solar absorbers

Abstract

In this work, it is shown the feasibility for obtaining silver nanoparticles by ultrasonic spray pyrolysis and their simultaneous incorporation during deposition of thin layers of aluminum oxide to get a Cermet coating of Al₂O₃-Ag. The synthesis of these Cermets was achieved on the basis of both the simultaneous pyrolysis of silver nitrate and aluminum acetylacetonate on different substrates: Quartz, glass, crystalline silicon (c-Si), and titanium at temperatures of 500, 550 and 600 °C. The optical and structural properties of the Cermets were studied by Scanning Electron Microscopy, Atomic Force Microscopy, X-ray diffraction, UV-vis, UV-vis-IR and FT-IR spectroscopies. UV-Vis spectroscopy showed that the intensity of the absorption peak (plasmon) was limited to the concentration of silver nitrate, and it shifted toward shorter wavelengths with the decrease in the size of the Ag nanoparticles inside the Cermets. The plasmon position of Ag nanoparticles in the different samples was found to be centered at 504 nm, 506 nm, 497 nm and 475 nm for samples deposited with 0.1 mol, 0.05 mol, 0.02 mol, and 0.01 mol of Ag(NO₃), respectively. The shape of the Ag nanoparticles was approximately spherical, ranging from 4 nm to 35 nm, and their concentration was proportional to the concentration of Ag(NO₃) included in the spray solution. By means of the UV-Vis Spectroscopy-IR and FT-IR, in the best of cases, a solar absorptance of 0.83 and an infrared thermal emittance of 0.14, for a sample of Al₂O₃-Ag prepared with 0.1 mol of Ag(NO₃) in the precursor solution, were obtained.