Development and degradation behavior of protective multilayer coatings for aluminum reflectors for solar thermal applications

The fabrication of multilayers Al-SiO2, Al-SiO2-TiO2, Al-Ni-Ag-SiO2, Al-Ni-Ag-SiO2-TiO2 on anodized aluminum sheet by the combination of physical vapor deposition sputtering and sol-gel coating process has been done. The multilayers of very high reflectivity (95% or more) could be developed on Al. The Al mirror reflectivity has been enhanced to 95% by a thin coating of Ag on aluminum in between the substrate and transparent and protective layers of SiO2 and SiO2-TiO2 The degradation behavior of these multilayers in accelerated weathering condition and under salt spray with different hours of exposure vis a vis reflectance is investigated. These coatings showed higher reflectance and sustenance in accelerated weathering and salt spray environment making it potential multilayered coating for solar thermal applications.