AlCrON太阳能选择性吸收涂层的制备及性能研究

采用直流反应磁控溅射及空气中300℃热处理法在Cu基底上制备Al Cr ON太阳能选择性吸收涂层。对所制备涂层的光谱选择性吸收性能和热稳定性能进行表征,涂层的吸收比和发射比分别为0.921和0.075。结果表明涂层具有较高的光学性能。另外,空气中300℃、100 h热处理后涂层的光学性能几乎不变,表明该涂层适用于平板太阳集热器。     

Mo-SiO2太阳选择性吸收涂层的空气高温热稳定性

采用磁控溅射的方法制作Mo-SiO2太阳能选择性吸收涂层,测量了涂层经过空气高温退火前后在0.34～25μm波长范围内反射曲线的变化情况.刚沉积完的涂层,太阳吸收比达到0.95,发射比为0.093.在空气中500、600℃退火1h后,涂层反射曲线基本不变.在空气中700℃退火1h后,涂层光谱选择性恶化,太阳吸收比下降到0.91,发射比上升到0.6.通过扫描电子显微镜观察了单层Mo、单层SiO2以及SiO2覆盖Mo的样片薄膜在空气中不同温度退火前后的形貌变化,发现以上薄膜表面不再平整,甚至出现裂纹和薄膜脱落,成为Mo-SiO2选择性吸收特性恶化的主要原因.     

不锈钢衬底表面形貌对AlN/AlN-Cr/Cu太阳能选择性吸收涂层光热性能的影响

在数值仿真计算和实验两方面研究不锈钢衬底表面形貌对AlN/AlN-Cr/Cu太阳能选择性吸收涂层光热性能的影响。在数值仿真计算中,建立一维三角形光栅结构模型对衬底表面形貌进行简化,采用严格耦合波分析(RCWA)的方法,仿真计算并分析光栅深度T_z和周期T_x对涂层的太阳吸收比α和400℃热发射比ε的影响。实验上,制备具有不同深度和间隔起伏表面的不锈钢衬底,采用磁控溅射的方法在其上沉积相同结构参数的AlN/AlN-Cr/Cu太阳能选择性吸收涂层,测定涂层性能参数,并分析不锈钢衬底形貌对其的影响。数值计算和实验结果表明:对于一个在已优化涂层组分和厚度的AlN/AlN-CdCu太阳能选择性吸收涂层,不锈钢衬底表面起伏对涂层高温光热转换将产生不利的影响。随着不锈钢衬底表面平均起伏深度的增加,涂层的太阳吸收比α基本保持不变,而400℃时的热发射比ε则明显逐渐增大。为保证涂层有效的光热转化效率,建议不锈钢衬底表面起伏的深宽比T_z/T_x≤1/20,深度T_z≤0.2μm。     

太阳光谱选择性吸收涂层制备工艺探讨

探讨粘结层、吸收层、减反射层的制备工艺及基底粗糙度状态对太阳选择性吸收涂层性能的影响。采用磁控溅射法,以SS/AlN涂层为例,制备太阳光谱选择性吸收涂层,并测试性能。结果表明：合适的制备工艺可以提高膜层的结合力和涂层的整体性能,胶带粘贴无脱落,吸收比96%,500℃发射比10.5%,并证实基底的粗糙度对涂层的发射率基本无影响。     

太阳能热发电高温(≥550℃)光谱选择性吸收涂层研究进展

开发基于熔融盐热媒介质高温(≥550℃)光热发电技术是槽式聚光太阳能发电的最新发展趋势,而实现该技术的关键物质基础是研制出在高温工况条件下具有较高太阳吸收比、较低热发射比及热稳定性能优越的高温光谱选择性吸收涂层。该文对近年来国内外已用于或有望应用于550℃以上光热发电高温光谱选择性吸收涂层的研究进展进行简要评述,初步讨论高温环境下光谱选择性吸收涂层发生失效的可能机制,最后对我国高温光谱选择性吸收涂层基础研究及工业化发展中存在的主要难题进行简要分析和展望。     

先进太阳选择性吸收涂层的发展

槽式抛物面太阳场运行温度的提高,由400℃至＞450℃,能增加总太阳发电效率和减小槽式抛物面发电厂的发电成本.当前的太阳选择性涂层不具备在较高工作温度所需的稳定性和工作性能.本文目的是开发更有效的太阳选择性涂层,在高于450℃时有高的太阳吸收比(α＞0.96)和低的热发射比(在450℃时,ε＜0.07),他们在高于450℃是热稳定的,在空气中是理想的,且具有改善了耐久性和生产制造性,因此减少了成本,利用计算机辅助光学设计软件,使多层太阳选择涂层具有超过目标的光学性能(吸收比为0.959,450℃时发射比为0.070)和比一般商业涂层有更低的热损失,那些具有高热稳定性的材料用计算机模型化了,这些超过设定的目标1％的发射比约等于1.2％吸收比.关键问题是沉积涂层的方法,为了沉积这单独的一层层薄膜,为了模型化的选择性多层结构的原型,使用由离子束辅助(IBAD)和电子束(电子束)共同沉积,这是由于它的灵活性和低的材料成本,实验工作聚焦在模型化的高温太阳选择性涂层;沉积一个个单层和模型化的涂层;测量光、热、形貌和成分等性质,并利用数据使模型化和沉积特性的有效性;涂层再优化;测量涂层工作性能和耐久性,将描述开发一个耐久的和先进的选择性涂层的过程.     

全玻璃真空太阳能热管半球发射比测量及仪器

全玻璃真空太阳集热管内选择性吸收涂层的 发射比是个非常重要的光-热性能参数,GB/ T17049-2005规定太阳选择性吸收涂层的半球发射 比εh≤0．080(80℃±5℃)。这里讨论发射比的测量 方法及准确度。早期的办法是在生产集热管吸收     

红外分光光度计测量太阳吸收涂层80℃的发射比

采用红外分光光度计和专门设计的试片恒温器测量80℃时太阳选择性吸收涂层及金属涂层的反射光谱,采用黑体辐射普朗克函数积分计算得到该温度下试样的发射比。试样采用磁控溅射法在平面玻璃载片上制备。实际测量结果表明,该方法测量精度高,测量过程简便快捷。另外,红外分光光度计为通用仪器,反射光谱标样容易制备和计量校准。     

太阳能光谱选择性吸收薄膜高温性能衰减分析

对SiO_2/CrO_x/CrN_y/Al型太阳能光谱选择性吸收薄膜的热稳定性进行测试,分析薄膜在高温下的光学性能、表面及截面形貌、元素分布、微观结构等变化。在450℃下热处理300 h后采用SEM、AES、TEM等方法分析薄膜热处理后的微观结构、成分变化。结果表明,经热处理薄膜出现表面粗糙度增加、晶粒异常长大、亚层界面变模糊等变化。主要的衰减机制为薄膜在高温下O、N发生轻微扩散,另外经热处理后吸收层Cr结晶度略有增加。     

TiAlON太阳能吸收膜的制备及高温性能衰减分析

采用直流磁控溅射制备AlON/TiAlON(LMVF)/TiAlON(HMVF)/Cu型太阳能光谱选择性吸收薄膜,并对其光学性能及高温下的衰减机理进行研究。吸收膜沉积态的吸收比和发射比分别为0.951和0.045(100℃)。在500℃的大气气氛中热处理200 h后涂层的光学性能出现小幅衰减。主要的衰减机制为薄膜在高温下O、N和Cu发生轻微扩散及氧化。结果表明AlON/TiAlON(LMVF)/TiAlON(HMVF)/Cu型太阳能吸收膜具有良好的光学性能,可适用于CSP中高温发电及民用生活等方面。     

Selective absorbing surface for evacuated solar collector tubes

The absorptance of AlN-Al(absorbing coating)/Al solar spectrum(0.34 ≈ 2.5 μ m) selective absorbing surface, containing 8-layer AlN-Al composite materials and with distinctive or non-boundaries between the layers, deposited by sputtering technology and heat-treated at 400 °C (60min) is about 0.95 and its thermal emittance is close to 0.07 ≈ 0.08(80 °C). But on the condition that the absorptance is unchanged, the thermal emittance dropped to 0.04 for the AlN-Al coating composed of matel volum fractionic 0.42, 0.25 and 0.00 films.     

Computations of the optical properties of metal/insulator-composites for solar selective absorbers

Solar selective absorbers are very useful for photo thermal energy conversion. The absorbers normally consist of thin films (mostly composite), sandwiched between the antireflection layer and (base layer on) a metallic substrate, selectively absorbing in the solar spectrum and reflecting in the thermal spectrum. The optical performance of the absorbers depends on the thin film design, thickness, surface roughness and optical constants of the constituents. The reflectivity of the underlying metal and porosity of the antireflection coating plays important roles in the selectivity behavior of the coatings. Computer simulations, applying effective medium theories, have been used to investigate the simplest possible design for composite solar selective coatings. A very high solar absorption is achieved when the coating has a non-uniform composition in the sense that the refractive index is highest closest to the metal substrate and then gradually decreases towards the air interface. The destructive interference created in the visible spectrum has increased the solar absorption to 98%. This paper also addresses the optical performance of several metals/dielectric composites like Sm, Ru, Tm, Ti, Re, W, V, Tb, Er in alumina or quartz on the basis of their refractive indices. The antireflection coating porosity and surface roughness has been analyzed to achieve maximum solar absorption without increasing the thermal emittance. Antireflection layer porosity is a function of dielectric refractive index and has nominal effect on the performance of the coating. While, up to the roughness of 1×10⁻⁷ m RMS, the solar absorption increases and for higher roughness, the thermal emittance increases only.     

Spectral selectivity and accelerated life testing of Al-PbS solar selective surfaces

High absorptance and low thermal emittance selective surfaces have been formed by evaporating lead sulphide onto Al evaporated Al substrates. The dependence of selectivity, α/?, on thickness has been studied. The maximum selectivity was obtained for PbS thickness of 400 Å. The emissivity is found to increase with temperature. The coatings are stable up to a temperature of 240°C in air. Long term ultraviolet irradiation causes the photo-oxidation of PbS to PbSO₄ which results in the increase of emittance and a decrease in absorptance. When cycled between 0°C and 200°C, the coatings do not show any signs of degradation.     

中温太阳光谱选择性PbS涂层制备

对现有的中温太阳光谱选择性PbS涂层制备方法加以改进,直接在预处理过的铜片上化学镀PbS。首先,考察了反应温度、反应物浓度、加碱量和反应时间等对PbS涂层太阳吸收率α的影响,得到了制备PbS涂层的优化条件;然后,在PbS涂层上涂敷TiO2作为保护层,以延缓PbS涂层的氧化,对两种涂层表面进行了XPS和SEM分析。实验结果证明,在不明显影响吸收率的情况下,TiO2/PbS涂层的耐热性能、耐腐蚀性和耐磨性能比单纯PbS涂层有明显提高,从而达到既降低发射率又延缓涂层寿命的目的。     

Solution-chemical derived nickel–alumina coatings for thermal solar absorbers

A promising novel solution-chemistry method to fabricate spectrally selective solar absorber coatings has been investigated. The selectively absorbing film consists of nickel nano-particles embedded in a dielectric matrix of alumina. Ejecting a precursor solution of nickel and aluminum onto an aluminum substrate using a spin-coating technique followed by a heat-treatment, generated the solar absorber samples. Smooth and homogeneous films with a nickel content of 0 to 80 vol.% were produced. The optimal coating had a nickel content of 65%, a thickness of 0.1 μm and a particle size of 10 nm. The absorbing layer attained a normal solar absorptance, _sol, of 0.83 and a normal thermal emittance, _therm, of 0.03. Adding an anti-reflection layer on top of the first absorbing layer further enhanced the performance of the absorber. The optimum anti-reflection coated sample reached a solar absorptance of 0.93 and a thermal emittance of 0.04.     

Optical properties and thermal stability of TiAlN/AlON tandem absorber prepared by reactive DC/RF magnetron sputtering

Spectrally selective TiAlN/AlON tandem absorbers were deposited on copper and stainless steel substrates using a reactive DC/RF magnetron sputtering system. The compositions and thicknesses of the individual component layers were optimized to achieve high absorptance (α=0.931-0.942) and low emittance (ε=0.05-0.06) on copper substrate. The experimental spectroscopic ellipsometric data have been fitted with the theoretical models to derive the dispersion of the optical constants (n and k). In order to study the thermal stability of the tandem absorbers, they were subjected to heat treatment (in air and vacuum) for different durations and temperatures. The tandem absorber deposited on Cu substrates exhibited high solar selectivity (α/ε) of 0.946/0.07 even after heat treatment in air up to 600 °C for 2 h. At 625 °C, the solar selectivity decreased significantly on Cu substrates (e.g., α/ε=0.924/0.30). The tandem absorber on Cu substrates was also stable in air up to 100 h at 400 °C with a solar selectivity of 0.919/0.06. Studies on the accelerated aging tests indicated that the activation energy for the degradation of the tandem absorber is of the order of 100 kJ/mol.     

Optical properties and thermal stability of pulsed-sputter-deposited AlxOy/Al/AlxOy multilayer absorber coatings

Spectrally selective Al_xO_y/Al/Al_xO_y multilayer absorber coatings were deposited on copper (Cu) and molybdenum (Mo) substrates using a pulsed sputtering system. The Al targets were sputtered using asymmetric bipolar-pulsed DC generators in Ar+O₂ and Ar plasmas to deposit an Al_xO_y/Al/Al_xO_y coating. The compositions and thicknesses of the individual component layers were optimized to achieve high solar absorptance (α=0.950-0.970) and low thermal emittance (ε=0.05-0.08). The X-ray diffraction data in thin film mode showed an amorphous structure of the Al_xO_y/Al/Al_xO_y coating. The X-ray photoelectron spectroscopy data of the Al_xO_y/Al/Al_xO_y multilayer absorber indicated that the Al_xO_y layers present in the coating were non-stoichiometric. The optical constants (n and k) of the multilayer absorber were determined from the spectroscopic ellipsometric data. Drude's free-electron model was used for generating the theoretical dispersion of optical constants for Al films, while the Tauc-Lorentz model was used for modeling optical properties of the dielectric Al_xO_y layers. In order to study the thermal stability of the Al_xO_y/Al/Al_xO_y coatings, they were subjected to heat treatment (in air and vacuum) at different temperatures and durations. The multilayer absorber deposited on Cu substrates exhibited high solar selectivity (α/ε) of 0.901/0.06 even after heat-treatment in air up to 400 °C for 2 h. At 450 °C, the solar selectivity decreased significantly on Cu substrates (e.g., α/ε=0.790/0.07). The coatings deposited on Mo substrates were thermally stable up to 800 °C in vacuum with a solar selectivity of 0.934/0.05. The structural stability of the absorber coatings heat treated in air (up to 400 °C) and vacuum (up to 800 °C) was confirmed by micro-Raman spectroscopy measurements. Studies on the accelerated aging tests suggested that the absorber coatings on Cu were stable in air up to 75 h at 300 °C and the service lifetime of the multilayer absorber was predicted to be more than 25 years. Further, the activation energy for the degradation of the multilayer absorber heat treated for longer durations in air is of the order of 64 kJ/mol.     

Theoretical efficiencies of angular-selective non-concentrating solar thermal systems

This paper explores the thermodynamic limits of solar thermal systems using absorber surfaces with high angular selectivity. It shows that theoretical considerations regarding the behavior of non-concentrating solar thermal systems are not enough in themselves to rule out their use in high-temperature applications. In fact, the paper demonstrates that the maximum theoretical thermal efficiency of a non-concentrating system may equal that of a concentrating system if the monochromatic directional emittance of its absorbing surface is sufficiently restricted. It is thus confirmed that the fundamental parameter that determines the ability of a solar-energy system to operate at high temperatures is not optical concentration, but angular selectivity of emittance.     

The preparation process and property analysis of a solar selective absorbing surface on milled steel

A solar selective absorbing surface is introduced processed by the alternating current oxidation method on cold-rolled milled steel plate. The performance of the surface, such as the solar absorptance , the thermal infrared emittance ε, the durability aging and the humidity resistance was tested and evaluated. Furthermore, the morphology and constitution of the solar absorbing surface were analyzed by transmission electron microscopy (TEM), Auger electron spectroscopy (AES), and Mössbauer spectroscopy. The results showed that the alternating current oxidation method can prepare solar selective absorbing surfaces that meet the requirements for use in low temperature solar applications.     

Corrosion protection of Sunselect, a spectrally selective solar absorber coating, by (3-mercaptopropyl)trimethoxysilane

The formation of a protective layer from (3-mercaptopropyl)trimethoxysilane (MPTMS) on commercial Sunselect, cermet-based spectrally selective coating (Alanod, DE), was studied by non-electrochemical (infrared reflection–absorption—IR RA, X-ray photoelectron spectroscopy—XPS), electrochemical (cyclic voltammetry (CV) in the presence of a redox probe (Cd⁺²), and potentiodynamic (PD)) techniques. By simple immersion and subsequent dip coating of the Sunselect substrate in the MPTMS sol, the hydrolyzed MPTMS precursor was adsorbed on the substrate, forming a protective layer imparting corrosion stability to Sunselect in a salt spray chamber for at least 20 days, outperforming any other sol–gel coating used so far for the corrosion protection of Sunselect. This was attributed to the penetration of MPTMS into the porous cermet structure through the upper antireflective Sn-oxide layer, as shown from XPS depth profile. Detailed analysis of the hydrolysis and condensation reactions of the MPTMS precursor by ²⁹Si NMR and IR spectroscopic techniques is reported.The most important finding was the observation that the applied MPTMS layer did not affect the spectral selectivity, as inferred from the solar absorptance increase of 1% and thermal emittance increase of not more than 2%.