Abstract
The world is moving at a fast pace in the consumption of non-renewable natural resources, causing several ecological problems. The search for the cost reduction by implementing renewable energies implies in the optimization of the manufacturing processes parameters of consolidated technologies, such as solar thermal energy collectors. One of the applications of selective surfaces is to improve performance of solar absorbers. The purpose of this work is to produce selective coatings with high absorption in range of UV/Vis and low emittance in the IR range. It was prepared a selective surface composed of ilmenite deposited on substrates of AISI 304 stainless steel using technique of cathodic cage plasma nitriding/deposition for application in solar thermal absorbers. Ilmenite was initially characterized by X-Ray Diffractometry (XRD), X-Ray Fluorescence (FRX) and Thermal Analysis (TGA). The coatings produced were optically characterized in range UV/Vis/IR and emittance and data on the roughness parameters of the films were obtained by Optical Profilometry. Selective surfaces with high solar absorbance (87%) compared with state-of-the-art commercial ones (70-80%) and low thermal emission (14%) compared with state-of-the-art commercial ones (20-30%) were obtained by validating the potential of ilmenite to produce selective surfaces for thermal solar collectors.
Highlights
Most of the energy used by humanity comes from fossil fuels, and the use of such energies, on a large scale, has considerably changed the environmental conditions of the planet
The differences between the compounds in the sample and the impurities contained in the mineral itself are related to the mineral origin of the ilmenite
The analysis by X-ray diffraction show that is in mineral chemical constitution, the main phases found in the compound are ilmenite (FeTiO3), followed by some peaks of Rutile (TiO2)
Summary
Most of the energy used by humanity comes from fossil fuels, and the use of such energies, on a large scale, has considerably changed the environmental conditions of the planet. The study of renewable sources of energy has become extremely relevant ahead of the growing world demand for energy[1]. Among these sources, solar energy stands out. One of its forms of exploitation is using solar collectors, which promote the conversion of solar energy into thermal energy[2]. The efficiency of these collectors is compromised due to a large loss from the emission of thermal radiation, resulting in operating temperatures below 100°C and limiting their applicability[3]. The selective surfaces absorb the maximum possible radiation in the ultraviolet, visible and near infrared (UV-Vis-NIR) range of the electromagnetic spectrum[4], while emitting little in the medium and distant infrared region, that is, they have absorption above 85% and emission below 15% in the mentioned wavelength bands[5]
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