等离子喷涂与溶胶-凝胶法组合制备中高温太阳能选择性吸收复合涂层

为了制备出高效的非真空、中高温太阳能选择性吸收涂层,先在光亮Cu片上等离子喷涂Cr—Al2O3金属陶瓷吸收层,再用溶胶-凝胶法在其上制备了SnO2选择性透过膜,对复合涂层的相结构、表面形貌、光学性能进行了研究。结果表明：金属陶瓷吸收层由金属颗粒Cr与Al2O3组成,物相稳定,表面凹凸不平,气孔较多,发射率较高;覆盖Sn...     

铬-氧薄膜及其太阳选择性吸收涂层

采用直流磁控反应溅射技术,获得了三种铬-氧薄膜复合材料。反应蒸发得到了两种铬-氧薄膜复合材料。用测厚仪与分光光度计法确定了波长在0.4-2.5微米范围内这些薄膜材料的光学常数n、k(复折射率n-ik)。其中第三种溅射铬-氧薄膜(C_rO3)的能带间隙约1.leV (A-D)和1.4eV(H-T)。从这些铬-氧薄膜材料的n、k数据,计算与设计了太阳选择性吸收涂层。得到以铝为底层的铬-氧选择性吸收涂层的最佳太阳光吸收率a≈0.91(AM2),这与实际制备的铬-氧选择性涂层的吸收率是一致的。直流磁控反应溅射制备的SiO_X薄膜,其成分接近SiO_2。经确定SiO_2薄膜的n≈1.5,k<0.01。SiO_2作为减反射膜沉积在上述的铬-氧选择性涂层上,其太阳吸收率a(AM2)≈0.94,室温发射率ε=0.04,故a/ε达23.5。     

真空集热管中的黑铬选择性吸收薄膜

本文介绍了用于太阳能全玻璃真空集热管中的真空沉积黑铬选择性吸收薄膜。试验了不同的工艺条件对此薄膜光学性能的影响,并进一步研制成双层的真空沉积黑铬选择性薄膜,它具有89％～91％的太阳吸收率α_s和小于5％(80 ℃)的红外法向发射率ε_n。该薄膜经一小时、300℃～400℃温度的真空烘烤后,其αS和ε_n基本没有变化。应用椭圆偏振光谱仪,在三个波长下对铝衬底及各层薄膜的光学常数进行了测定和计算,并用上述结果计算了这些波长下的整个双层黑铬薄膜的反射率,其结果与分光光度计实测的反射率相符。同时还测定了各层薄膜的透过率τ(λ)。这些结果表明,上面一层黑铬薄膜具有减反射作用,因而使双层黑铬薄膜比单层黑铬薄膜具有更高的吸收率,并仍保持其低的红外发射率。对由真空沉积双层黑铬薄膜所试制的真空集热管进行了热性能试验。结果表明,沉积双层黑铬的管子的集热性能优于单层黑铬管,其闷晒的集热性能优于同类型的国外产品。     

TiAlN/SiO2太阳能选择性吸收薄膜的制备与研究

采用直流磁控溅射法在铜基底上制备了TiAlN/SiO2选择性吸收薄膜。通过调整制备过程中的工艺参数,得到优化后的组合薄膜(铜基底),其吸收率可达0.92、发射率为0.06。在此组合膜系中,TiAlN为吸收层,SiO2为减反层。对基底为铜片的样品在550℃退火2h,其性质保持稳定,表明TiAlN/SiO2组合薄膜在高温太阳能选择性吸收领域具有一定的应用前景。     

镍-铬复合溶胶的制备及其在高发射率涂层中的应用

首先合成了镍-铬复合溶胶,然后向其中掺杂纳米SiC粉末得到喷涂用涂料,进而在镍基高温合金上制备了NiO-Cr2O3-SiC红外高发射率复合陶瓷涂层.结果表明,该涂层有很高的发射率,与基材结合良好,抗热震性能明显优于Al2O3-SiC陶瓷涂层.     

常规和纳米ZrO_2-7%Y_2O_3等离子喷涂热障层及其激光重熔后的抗热震性能

为了探讨激光重熔对等离子喷涂常规和纳米热障涂层(TBCs)的影响,采用等离子喷涂工艺在γ-TiAl合金表面制备了常规和纳米ZrO2-7%Y2O3TBCs,并对其进行激光重熔处理,研究了等离子喷涂常规TBCs、激光重熔-等离子喷涂常规TBCs、等离子喷涂纳米TBCs及激光重熔-等离子喷涂纳米TBCs 4种涂层在850℃下的抗热震性能。结果表明:4种TBCs热震失效次数依次为73,118,146,163次,相应的热震破坏形式分别为整体剥落、局部剥落、边角剥落和局部剥落;纳米结构有利于提高涂层的抗热震性能;激光重熔在一定程度上改善了等离子喷涂层的抗热震性能。     

微结构对太阳能选择性吸收薄膜性能的影响

介绍了制备光热太阳能选择性吸收薄膜的条件及薄膜的制备方法。采用二次阳极氧化方法在铝基底上制备了多孔微结构,再利用磁控溅射制备SS-AlN多层膜。用SEM、Optsol Absorber Control等测试手段表征了膜系的表面形貌、光谱吸收性能等,考察了微结构对太阳能选择性吸收薄膜性能的影响。结果表明基底表面微结构能有效提高其光谱吸收率。     

NiSiO_2太阳光谱选择吸收涂层的设计制备及热稳定性研究

采用软件模拟辅助实验的方式制备了新型Al/NiSiO_2(M)/NiSiO_2(D)/SiO_2太阳光谱选择吸收涂层,并对其热稳定性进行了研究。使用磁控溅射技术,通过改变氧气(O_2)流量制备了一系列NiSiO_2膜层,研究了O_2流量对膜层光学性能的影响,并使用光学模拟软件对涂层进行设计和优化。根据模拟优化结果在不锈钢基底上成功制备了Al/NiSiO_2(M)/NiSiO_2(D)/SiO_2光谱选择吸收涂层,其吸收率(α)为0.933,400℃下的发射率(ε)为0.14。涂层在空气中450℃高温下热处理100h后,其吸收率与发射率之比(α/ε)由6.66上升至7.62,依然保持着较高的光谱选择性,表明涂层具有较好的热稳定性。     

电化学表面技术在太阳能热转换中的应用

评述了电化学表面技术在太阳能热转换光谱选择性涂层中的应用，包括黑铬、黑镍、黑钴电镀，铝氧化，钢铁和铜钝化等工艺及光学性质。并对涂层厚度的优化、基体的影响、膜导电性能与发射率的关系进行了探讨。     

Al2O3-Cr多层中高温选择吸收薄膜的研究

太阳能选择吸收薄膜是太阳能集热器的关键部分,本文提出基于Al2O3介质和金属Cr的多层结构的选择吸收膜系,首先采用电子束热蒸发在硅基底上沉积了单层Cr薄膜,通过椭偏仪测试并分析了Cr薄膜的光学常数.在此基础上分别设计了Al2O3-Cr四层和六层选择吸收膜系,比较了两种膜系的吸收率和发射率.其次,对六层结构的选择吸收膜系进行了允差分析,给出了最敏感层厚度相对误差为20％时,选择吸收膜的吸收率和发射率.最后,采用电子束热蒸发技术在玻璃基底上制备了六层结构的选择吸收膜,测试结果表明,该膜系在常温下的吸收率可以到达0.96,发射率为0.043.并通过计算给出了制备的六层选择吸收膜在100,200,300,400,500℃下的发射率分别为0.045,0.052,0.063,0.071和0.092.     

The development of high performance,low cost solar-selective absorbers

In this paper the first results of a project concerned with the development of low cost transition metal nitride selective absorbers with a high solar absorptance and a low thermal emittance are presented. These absorbers are intended for application at operating temperatures up to 200 °C in high performance solar collectors.We found that reactively d.c.-sputtered chromium nitride films on a copper substrate exhibit a low emittance (about 0.04) and a moderate solar absorptance (about 0.80). The relatively high production cost and capital investment associated with sputtering can be avoided by producing such films by (electro)chemical deposition. Encouraging results have been obtained with the nitridation of electrodeposited chromium films.The drawback of the moderate solar absorptance can be overcome by depositing the nitride films onto electrodeposited rough copper base layers. We found that the addition of small carbon particles (india ink pigment) to the copper deposition bath gives rise to layers with a suitable surface roughness. This surface roughness causes the solar absorptance to increase to 0.90. However, because of the small characteristic dimensions (about 0.5–2 μm) of the roughness, the low thermal emittance is hardly affected.     

Influence of solvents on properties of solar selective coatings obtained by spray pyrolysis

Solar selective coatings for solar thermal flat-plate collectors consisting of crystalline copper oxides and amorphous nickel oxide composites were obtained by robotic spray pyrolyzed deposition. The parameters were optimized for increased spectral selectivity (S): high solar absorptance and low thermal emittance. The coatings were deposited using nickel and copper acetate, dissolved in mixed solvents with various water: ethanol ratios. The coatings’ properties were characterized in terms of crystalline composition (XRD), surface morphology (AFM, contact angle) and optical properties (solar absorptance, thermal emittance and spectral selectivity). Considering the precursor solutions composition (solvent, wetting behaviour), the growth processes were modelled for two different systems: predominant hydrophilic and predominant hydrophobic. The high selectivity values (S > 30) of the optimized composite coatings were explained based on two parallel mechanisms: intrinsic absorption and multiple reflections generated when absorbers with controlled roughness are deposited.     

Spectrally selective absorber coating from transition metal complex for efficient photothermal conversion

Copper–manganese oxide (CuMnO _x ) thin films are proposed as efficient and thermally stable selective solar absorbers. The coatings were deposited on aluminum, stainless steel, and glass substrates by dip-coating method from the alcoholic solution of the Cu and Mn nitrate. An organic filmogen was introduced in order to get better adherence with the substrate hence to get uniform films even for larger substrates. The coated films were dried and subsequently heat-treated at 500 °C. X-ray diffraction spectra of the annealed film showed the formation of pure Cu–Mn oxide spinel structure (Cu_1.5Mn_1.5O₄) in the film. FTIR spectra show complete removal of the organic species after thermal treatment at 500 °C. The solar absorptance and thermal emittance were calculated from the hemispherical reflectance spectra in the UV/Vis/NIR and IR range, respectively. The maximum visible absorptance with minimizing the infrared thermal emittance was optimized by controlling the thickness of the films, choosing substrates, and introducing a SiO₂ overlayer.     

Solar selective black molybdenum coatings by chemical conversion

Solar selectivity, with emphasis on a high solar absorptance and a low thermal emittance, was measured for black molybdenum films prepared by a chemical conversion process. The best values of the solar absorptance (0.88) and the thermal emittance (0.20) were achieved by optimizing the preparation parameters, e.g. the bath composition, the deposition temperature and the immersion time. The films deposited onto galvanized steel sheet and zinc-plated mild steel sheet show high adherence and good thermal stability at elevated temperatures (250 °C).     

Preparation of solar selective absorbing coatings by magnetron sputtering from a single stainless steel target

This paper presents a method to prepare solar selective absorbing coatings by radio frequency magnetron reactive sputtering using a single stainless steel target. Stainless steel/stainless steel nitride (SS/SS-N) ceramic-metal composite (cermet) thin films were produced under varied nitrogen gas flow ratios. The solar selective absorbing films have good solar absorptance of 0.91 and thermal emittance of 0.06 at 82 °C. The refractive index (n) and extinction coefficient (k) of the cermet composite layers prepared in nitrogen and argon atmospheres were determined by spectroscopic ellipsometry. The films were also analyzed by different oscillator models. The results showed a significant transformation from metal to cermet as the nitrogen gas flow ratio was increased to 10%. As the nitrogen gas flow ratio was increased to 17.5%, the film became a dielectric layer that could be used as an anti-reflection layer, suitable as the outermost layer of the solar selective absorbing coatings. A theoretical solar absorptance of 0.92 was achieved by selecting an appropriate combination of three solar absorbing layers. The experimental results agreed well with the theoretical calculations. This study proved the possibility of preparing solar selective absorbing coatings with high solar absorptance by using a single stainless steel target.     

Stability of coatings of low atomic number under irradiation

A detailed study of the structural, thermal and optical properties of selective black nickel coatings on galvanized iron was carried out. The spectral reflectances of the coatings in the visible and infrared regions were measured with an integrating sphere reflectometer. Deposition parameters were optimized to achieve high solar absorptance (α = 0.94) and low emittance (ε = 0.09 at 100°C). Temperature cycling and humidity tests established long-term durability of the coatings for solar thermal conversion applications.     

Absorbeurs selectifs de l'energie solaire elabores a partir d'acier inoxydable : Influence de la composition chimique et de l'etat metallurgique de l'alliage sur les proprietes optiques

Efficient photothermal converters exhibit high solar absorptance and low thermal emittance. An original method has allowed spectrally selective coatings to be obtained by chemical conversion of stainless steel. These coatings exhibit high selectivity (absorptance higher than 95 % and emittance lower than 20 %) and excellent durability.The dependance of the optical properties of these coatings on the chemical composition and metallurgical state of the substrate is studied. Low emittance appeared to be closely related to the corrosion resistance of the metallic surface in the treatment bath. Owing to this fact, convenient conditions can be found to produce selective coating for each alloy.     

Optimization and microstructural analysis of cobalt-sulfide-pigmented aluminum oxide

Porous anodic films formed on aluminum in a phosphoric acid electrolyte were used to develop selective solar coatings by double precipitation of cobalt acetate and ammonium sulfide indide the pores. The black coatings containing cobalt sulfide were then sealed in hot water and their optical, mechanical and thermal degradation properties were tested. Multiple linear regression routines were used to optimize the absorptance and emittance values and the coating formation conditions were accordingly adjusted. After optimization, the coatings were characterized by scanning and transmission electron microscopy, and thermal stability tests were performed to determine the long-term quality of the coatings. The coatings were found to have good thermal stability up to 150°C and high adhesion strength as well as absorptances of up to 0.965 at emittances ranging from 0.15 to 0.25.     

Hochselektive Absorberschichten für thermische Sonnenkollektoren

High‐selective absorber coatings for solar thermal collectors Highly selective absorber coatings are necessary for the effective operation of state‐of‐the‐art solar thermal collectors. The thin film gradient optical coating with its spectrally selective characteristics achieves high solar absorptance combined with low thermal emittance. Such complex multi‐layer systems are produced in modular vacuum coating processes. Industrial air‐to‐air coating lines allow the continuous coating of metal bands in a pass‐through process and provide absorber coatings which meet highest demands for efficiency, durability and esthetics.     

Titanium–aluminum–nitride coatings for satellite temperature control

Intense solar irradiation, radiative cooling to outer space, and internal heat generation determine the equilibrium temperature of a spacecraft. The balance between the solar absorption and thermal emittance of the surface is therefore crucial, in particular for autonomous parts directly exposed to the solar radiation and thermally insulated from the main thermal mass of the spacecraft. The material composition but also the coating thickness are found to influence the equilibrium temperature of an object in space. In this paper we report on a systematic search for a suitable composition and thickness of Ti_xAl_yN_z alloy coatings prepared by reactive, unbalanced magnetron sputtering from targets consisting of differently sized titanium and aluminum sectors. The films were deposited on glass, glassy carbon, aluminum sheet metal, and on sputtered aluminum and Ti_xAl_(1−x) films on glass. The stoichiometry and sheet resistance of the films was determined with Rutherford backscattering and four-point probe measurements respectively. Reflectance spectra for the visible and infrared spectral ranges were used to obtain average solar absorptance and thermal emittance values used in model calculations of the equilibrium temperature. Neglecting internal heat contributions, the lowest calculated equilibrium temperature in orbit around the Earth, 32.5°C, was obtained for a 505-nm-thick Ti_0.14Al_0.47N_0.40-film.