Deterioration of Novel Silver Coated Mirrors on Polycarbonate Used for Concentrated Solar Power

Abstract

The lifetime of mirrors in outdoor conditions is crucial in the correct operation of any concentrating solar power (CSP) installation. In this work, the corrosion behavior of two types of metallized surfaces was studied. The first was made of a flexible polymer having a deposited reflective silver metallic film. The second was made of the same surface type with a dielectric SiO2 protection coating by an atmospheric pressure plasma jet. Polycarbonate sheets were used as substrates on which metallic silver was deposited by the Dynamic Chemical Deposit technique. This electroless technique allowed producing the mirror finishing under environmental conditions by sequentially spraying; as aerosols projected towards the substrate surface, the activation and reducing-oxidizing solutions with rinsing after each one. The silver coatings were about 100 nm thick. Environmental and accelerated weathering degradation and salt and sulfide fogs were carried out. XPS analyses show that the corrosion products formed were Ag2S, AgCl, and Ag2O. It was observed that the tarnishing was initiated locally by the formation of Ag2S columns as eruptions on the surface. Subsequently, the ions diffused through the protective layer and into the silver reflective layer, chemically reacting with the silver. The main atmospheric agents were H2S, chloride particles, and HCl. High reflectance was initially obtained of about 95%. The obtained results suggest mechanisms for the degradation of exposed silver surfaces to moisturized atmospheres with corrosive compounds.