無電鍍複合鍍製備Al2O3-Black Ni 太陽光譜選擇性
複合吸收膜之性質探討

金屬-電介質複合吸收膜具高吸收性能而廣泛使用於太陽光集熱器，但因成本昂貴使得其應用受到限制。本研究利用製程簡單及價格便宜之無電鍍複合鍍技術，製備 Al2O3-Black Ni太陽光譜選擇性複合吸收膜於鋁基材上，利用Sol-gel法藉旋轉塗佈法在吸收膜表面上製備抗反射層。主要探討吸收膜中三種不同粒徑(300 nm、70 nm、15 nm)與添加量(4 g/L、8 g/L、16 g/L、24 g/L、28 g/L)之氧化鋁、複合吸收膜厚度和塗佈不同抗反射層SiO2和TiO2之氧化物，對複合吸收膜之吸收率(α)和熱輻射率(ε)的影響，最後以選擇性比值條件最佳進行環境測試。利用紫外光/可見光/近紅外光分光光譜儀(Uv-Vis-NIR)分析吸收膜在300 nm ~ 2500 nm波長範圍之反射率，傅立葉轉紅外線光譜儀(FTIR)分析吸收膜在4000 cm-1 ~ 500 cm-1波數(2500 nm ~ 20000 nm波長)範圍之反射率，以量測其吸收率與熱輻射率。使用掃瞄式電子顯微鏡(SEM)、原子力顯微鏡(AFM)、化學分析電子儀(ESCA)、表面輪廓儀(α - step)，觀察吸收膜表面電介質的分佈、厚度、表面粗糙度、分析吸收膜表面化學組成和抗反射厚度對光學性質的影響。添加粒徑300 nm氧化鋁濃度由8 g/L增加至28 g/L，吸收率由0.69增加至0.79，熱輻射率由0.08增加至0.11；添加粒徑70 nm氧化鋁濃度由8 g/L增加至28 g/L，吸收率由0.79增加至0.84，熱輻射率由0.13增加至0.20；添加粒徑15 nm氧化鋁濃度由4 g/L增加至16 g/L，吸收率由0.81增加至0.86，熱輻射率由0.09增加至0.15。粒徑15 nm，16 g/L之 Al2O3-Black Nickel 複合吸收膜厚度為2.7 μm時具最佳之光學性質，吸收率0.89，熱輻射率0.07，選擇性比值為12.71。以SiO2-0.5M做抗反射層塗佈於Al2O3-Black Nickel複合吸收膜上，其吸收率為0.92、熱輻射率為0.09，可得到比TiO2抗反射層較優異的光學性質。環境耐久測試以粒徑15 nm，16 g/L，厚度2.7 μm之Al2O3-Black Nickel 複合吸收膜進行24 h至75 h之300 ℃熱穩定及溼度95 %水氣凝結測試，結果顯示，經75 h熱穩定測試； Al2O3-Black Nickel 複合吸收膜光學性能比值由12.71衰退減少至9.4，Black Nickel吸收膜光學性能比值由17光學性能衰退至4.84，經水氣凝結測試；Al2O3-Black Nickel 複合吸收膜光學性能比值衰退減少至4.81，Black Nickel吸收膜光學性能比值衰退減少至5.61。

關鍵字

無電鍍鎳；抗反射層；複合吸收膜；吸收率；熱輻射率

並列摘要

The metal-dielectric composite spectrally selective solar absorbers were widely used in solar thermal collectors due to its excellent absorption. The manufacture cost of the metal-dielectric composite spectrally selective solar absorbers is expensive and that limits its applications. In this work, the electroless composite coating technology which possesses lower cost, simple equipment and easy to operate characteristics was used to fabricate the Al2O3-black nickel composite solar selective surface on Al substrate and the Sol-gel technique was used to fabricated the anti-reflection (AR) layer. The effects of the particle size(300 nm ,70 nm , 15 nm) and content(4 g/L , 8 g/L , 16 g/L , 24 g/L , 28 g/L) of Al2O3, the thickness of the Al2O3-Black nickel composite coatings and the AR layers of SiO2 and TiO2 on the optical properties of the absorbers were investigated. The Uv/Vis/NIR spectrophotometer was utilized to measure the reflectance of the absorbers in the wavelength interval of 300 – 2500 nm, and the FTIR spectrometer was utilized to measure that in the wavelength interval of 2500 – 20000 nm. SEM and AFM were used to observe the surface morphologies and the thickness of coatings. The chemical structures of coatings were studied by ESCA. The environment durabilities including thermal stability and humidity resistance of the samples with optimized optical properties were performed.. The content of 300 nm alumina increases from 8 g/L to 28 g/L , the solar absorptance α of Al2O3-Black nickel/Al absorber increase from 0.69 to 0.79, the thermal emittance ε increase from 0.08 to 0.11. The content of 70 nm alumina increases from 8 g/L to 28 g/L , the solar absorptance α increase from 0.79 to 0.84, the thermal emittance ε increase from 0.13 to 0.20. The content of 15 nm alumina increases from 4 g/L to 16 g/L , the solar absorptance α increase from 0.81 to 0.86, the thermal emittance ε increase from 0.09 to 0.15. The 2.7 μm Al2O3-Black Nickel composite coatings contained 16 g/L of 15 nm alumina have optimum optic properties, solar absorptance α = 0.89 and low emittance ε = 0.07, and high selectivity factor 12.71. The solar absorptance and thermal emittance of the Al2O3-Black Nickel/Al absorbers with SiO2-0.5M AR layers are 0.92 and 0.09, respectively. Those of the Al2O3-Black Nickel/Al absorbers with TiO2 AR layers are 0.83 and 0.19, respectively. The selectivity factor of Al2O3-Black Nickel/Al absorbers after 300 ℃thermal stability test for 75 h decreased from 12.71 to 9.4, and that of black Nickel/Al absorbers decreased from 17 to 4.84. After 95 % humidity condensation test for 75 h, the selectivity factor of Al2O3 - Black Nickel/Al absorbers decreased from 12.71 to 4.81, and that of Black Nickel/Al absorbers decreased from 17 to 5.61.