Efeitos do envelhecimento sobre a absortividade de superfícies seletivas solares à base de Cromo (CrxOy) depositadas via Magnetron Sputtering

Abstract

The northeast region has one of the highest incidences of solar irradiation in the country. Within this context, the exploration of this type of energy becomes interesting from the point of view of the development of new techniques capable of increasing the absorption capacity and utilization of solar radiation. Solar Collector is performed solar thermal conversion however it may present some limitations when it is intended to perform a heating at between average temperatures (100ºC-400ºC) or high (above 400ºC). This is because when heated in this range, the materials increase their thermal emissivity, consequently there are losses in the capture of solar radiation. To reduce these losses, Solar Selective Surfaces (SSS) are used as an alternative to solve this issue. These surfaces act in the absorption of solar radiation with wavelengths relevant to solar thermal conversion and not absorbing the spectrum range that causes thermal emission, allowing greater use of energy. In this sense, this study aimed to evaluate the absorptivity of Chromium-based SSS (CrxOy) when subjected to the heating process at medium temperatures. 12 films were deposited by Magnetron Sputtering on 304 stainless steel substrates and underwent a custom aging heat treatment. The characterizations were: UV-Vis and Infrared Spectrophotometry (FTIR), Optical Profilometry and X-Ray Diffraction. The results showed that most of the deposited films had average absorptance values above 93%. The non-aged sample S3 (Cr-Cr2O3, 60+200W – 30min) showed the best absorptance result (98.79%). The aging of the films at 250ºC provided improvements in the morphological and optical properties of the S2 sample (Cr2O3, 200W – 30min). The samples that were deposited with power variation, 60W+200W and 60W+200W+60W, showed similar morphologies.