Avaliação do comportamento óptico e da resistência a corrosão de superfícies seletivas solares

Abstract

Solar heat conversion has limits when it is designed to achieve high temperatures, which diminishes its overall efficiency. Selective surface coatings for absorber plates offer a promising solution by improving the energy gain-to-loss ratio of photothermal collectors. A comprehensive understanding of coating performance, including types, applications, fabrication parameters, and their influence on the corrosion resistance of absorber plates, is critical. This study presents a theoretical and experimental investigation into the optical behavior of Cr and Mo thin films, with and without a SiO₂ layer, deposited by magnetron sputtering on AISI 304 stainless steel substrates subjected to various surface treatments (electropolishing, mechanical polishing, and chemical passivation). Theoretical models demonstrated high accuracy in predicting the behavior of selective coatings. The optical characterization of the produced surfaces was performed across ultraviolet, visible, and infrared spectra. The results indicated higher optical selectivity for coatings deposited on mechanically polished substrates, with Cr/SiO₂ films achieving the highest selectivity (32.52). X-ray diffraction revealed martensitic crystalline peaks in mechanically polished substrates, resulting in a lower emissivity (2.98%). Electrochemical impedance spectroscopy further indicated enhanced corrosion resistance for Cr-based selective surfaces on electropolished substrates. The antireflective SiO₂ layer contributed not only to improved optical selectivity but also to increased corrosion resistance by providing an additional charge transfer barrier on the selective surfaces.