Selective Surfaces of Ilmenite for Use in Solar Absorbers

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.

摘要 当前全球非可再生自然资源的消耗速度日益加快，引发了诸多生态问题。为通过应用可再生能源实现成本削减，需对太阳能热集热器等成熟技术的制造工艺参数进行优化。选择性表面的重要应用之一，便是提升太阳能吸收器的性能。本研究旨在制备在紫外/可见光波段具备高吸收率、红外波段具备低发射率的选择性涂层。本次实验采用阴极笼式等离子体渗氮/沉积技术，在AISI 304不锈钢基底上制备了钛铁矿基选择性表面，用于太阳能热吸收器。研究首先通过X射线衍射（X-Ray Diffractometry, XRD）、X射线荧光光谱（X-Ray Fluorescence, FRX）与热重分析（Thermal Analysis, TGA）对钛铁矿原料进行了表征；随后对制备得到的涂层开展紫外/可见光/红外波段的光学特性表征，并通过光学轮廓仪获取了薄膜的粗糙度参数数据。最终获得的选择性表面太阳能吸收率达87%，优于当前主流商用产品的70%~80%；热发射率仅为14%，低于商用产品的20%~30%，验证了钛铁矿用于制备太阳能热集热器选择性表面的应用潜力。