- 學位論文
Al2O3-NiP太陽光譜選擇性複合吸收膜之性質探討
The Study of Al2O3-NiP Solar Spectrally Selective Composite Films
摘要
高效能的太陽能集熱器利用太陽光譜選擇性吸收表面吸收太陽輻射，並將其轉換成熱能。但是，太陽能集熱器的成本昂貴以至於限制了其應用。在本實驗中，利用成本低、設備簡單的無電鍍複合鍍技術在鋁基材上製備Al2O3 - NiP太陽選擇性複合吸收表面；並利用溶膠凝膠技術製備抗反射(AR)層、黑化處理達到吸收層表面粗糙效果，期能改善並提升Al2O3 – NiP吸收層的光學性質。 不同pH值的酸(pH4.5、pH5.5)、鹼(pH9.7、pH10.7)型吸收層，利用改變Al2O3含量(0 vol.%, 11vol.%, 17vol.% , 19vol.%)、膜厚(0.5、1.0、2.0μm)，以及後續的黑化處理、塗佈SiO2與TiO2抗反射層對於吸收層光學性質的影響皆在此實驗中作研究並討論。酸型Al2O3 – NiP吸收層的環境耐久性測試，是分別利用熱穩定性以及耐濕性兩部分來做測試，並比較光學性質變化。 利用分光光譜儀測量吸收層在波長範圍300~2500 nm的反射率及傅立葉轉換遠紅外光光譜儀測量波長2500~15000 nm範圍內的反射率，求得吸收率(α)與熱輻射率(ε)。SEM觀察吸收塗層的表面形貌和膜厚。 酸型吸收層增加Al2O3含量從0 vol.%到17 vol.%，其吸收率與熱輻射率皆呈現提升的趨勢；膜厚方面，酸型吸收層之吸收率隨著膜厚的減少而有提升的現象；黑化處理部分，pH4.5吸收層經硝酸黑化處理之吸收率可達0.82，pH5.5吸收層之吸收率可高達0.96；塗佈抗反射層方面，塗佈SiO2與TiO2抗反射層之吸收率隨著塗佈膜厚的減少而有提升的現象，熱輻射則是隨著膜厚的減少而有減少的趨勢。pH5.5吸收層之黑化試片經熱穩定性與溼度凝結測試，其性質未有明顯下降的現象。 鹼型吸收層增加Al2O3含量從0 vol.%到17vol.%，有光學性質提升的趨勢；鹼型吸收層之吸收率有隨著膜厚的增加而提升的現象；經硝酸黑化處理之pH9.7吸收層，其吸收率可高達0.95，pH10.7吸收層之吸收率可達0.93。塗佈SiO2與TiO2抗反射層之吸收率隨著膜厚的減少而有提升的現象，熱輻射則是隨著膜厚的減少而有減少的趨勢。
並列摘要
Spectrally selective surfaces have used in solar thermal collectors for absorbing solar radiation and converting it into heat. However, the cost of thermal solar collector is expensive, that limits the applications of solar thermal collector in solar photothermal conservation. In this work, composite electroless deposition was used to fabricate the Al2O3-NiP composite solar selective surfaces on Al substrates to form Al2O3-NiP/Al absorbers due to its cost is inexpensive and equipment is simple. The anti-reflection (AR) layers fabricated by Sol-gel technique and the blacking process used to rough the surface of samples were used to enhance the optical properties of Al2O3-NiP/Al absorbers. Effects of the pH value of deposition solution, the Al2O3 content (0, 11, 17 and 19vol.%) and the thickness (0.5, 1.0, 2.0μm) of Al2O3-NiP films, blacking process and the AR layer on the optical properties of the Al2O3-NiP/Al absorbers were investigated. The environmental durability of Al2O3-NiP/Al absorber was characterized by the thermal stability and the humidity resistance.The UV/Vis/NIR spectrophotometer was used to measure the solar absorptance (α) of the absorbers in the wavelength interval of 300 – 2500 nm, and the FTIR spectrometer was utilized to measure the thermal emittance (ε) in the wavelength interval of 2500 – 15000 nm. SEM was used to observe the surface morphology and the thickness of absorber coatings. When Al2O3-NiP films were deposited in pH4.5 and pH5.5 solutions, the α and ε increased with increasing of Al2O3 content from 0 to 19 vol.%, and those decreased with increasing of thickness from 0.5 to 2.0 μm. The α and ε increased with increasing of blacking time during blacking process and those decreased with decreasing of AR layers thickness. The results of a thermal stability test and a condensation test revealed that the blackened Al2O3-NiP/Al solar absorber which prepared in pH5.5 had excellent durability. When Al2O3-NiP films were deposited in pH 9.7 and pH 10.7 solutions, the α and ε increased with increasing of Al2O3 content from 0 to 17 vol.%, and those decreased with increasing of thickness from 0.5 to 2.0 μm. The α and ε increased with increasing of blacking time during blacking process and those decreased with decreasing of AR layers thickness.