Selective Surfaces of Black Chromium for Use in Solar Absorbers

Abstract

One of the applications of selective surfaces is to improve performance of solar absorbers. The purpose of this work is to produces selective coatings with high absorption of solar radiation in the range of UV/Vis/NIR. It was prepared a selective surface composed of black chromium (Cr/Cr 2 O 3 ) deposited on substrates of AISI 304 stainless steel using the technique of electrolytic deposition for application in solar thermal absorbers. The great parameters for deposition consisted of a continuous electric current of 2A for 90s, at a constant temperature of 40°C. After deposition, the samples under went to a heat treatment at 600°C for 2h for oxidation. The coatings thicknesses were determined. From the SEM analysis coupled with EDS, it was found that the microstructures reported sample of cermets. The XRD results show diffraction peaks related to metallic chromium (Cr) and chromium oxide (Cr 2 O 3 ). Spectral absorptance values more 90.0% were found.

Efeitos Do Pós-Tratamento Térmico Em Superfícies Seletivas À Base De Óxidos De Cromo Obtidas Pelo Processo De Eletrodeposição

“…Os resultados obtidos corroboram com os estudos de Nunes et al (2018) que ao aplicarem a técnica de difração de raios-x em amostras de cromo eletrodepositadas sobre substratos de aço inoxidável AISI 304 seguido de um tratamento térmico a 600ºC por duas horas, observaram a formação das fases correspondentes ao cromo metálico e ao Cr 2 O 3 . Assim como nos resultados obtidos nesse trabalho, Nunes et al (2018) também não identificaram a presença de Cr 3 O nos padrões de difração das amostras submetidas a tratamento térmico, fato que pode ser explicado pela transformação dessa fase em uma fase mais estável (Cr 2 O 3 ) durante esse processo. A formação de Cr 2 O 3 está diretamente relacionada com a qualidade dos filmes depositados.…”

“…Entretanto, poucos autores têm discutido a utilização de tratamentos térmicos pós-deposição, que simulem o envelhecimento das superfícies, e analisem o comportamento dos óxidos de cromo, quando submetidos a esses tratamentos (PETTIT, 1983;GAO et al, 2016, ZHANG et al, 2017. Segundo Nunes et al (2018) o pós-tratamento térmico facilita a obtenção de óxidos de cromo, que está diretamente relacionado com a qualidade dos filmes obtidos, e um aumento da absortância.…”

Evaluation of Potential Residual Silica as Antireflective Layer for Selective Solar Surface of Black Chromium

“…Many methods had been used to prepare selective absorbers, such as electrodeposition, sputtering, evaporation, pyrolysis, painting and sol-gel 7 . This study opted for the use of the electrodeposition technique due to the simplicity of the equipment used and its low cost, the good optical proprieties (absorptance and emittance) of the obtained coatings, in addition to the technique being able to the realized at ambient temperature and atmospheric pressure, which makes it particularly attractive for industrial applications 8 .…”

Optimizing effectiveness and robustness for solar heat absorbers composed of a periodically nano-structured surface

“…Cheng et al [5] presented a photoexcited switchable absorber composed of X-shaped gold structures and a silicon pad. Nunes et al [24] demonstrated a selective surface composed of black chromium (Cr/Cr 2 O 3 ) deposited on substrates of AISI 304 stainless steel for solar heat absorption. Tian et al proposed a one-dimensional HfO 2 / Al 2 O 3 -W nanocomposites/W/Al 2 O 3 /W multilayered photonic structure as potential wavelength-selective thermal devices.…”