Aluminum ultraviolet reflectance

But metallic coatings have high absorption losses. But one can remedy them with dielectric coatings, which are necessary also to passivate the metal, avoiding oxidation. Aluminum is the best metal for the ultraviolet in addition it adheres on most substrates it needs passivation. Silver is easy to deposit it has the highest reflectance in the visible and the infrared since it tarnish rapidly, passivation is mandatory. Gold is the best material beyond 700 nm, and it is considered that it does not tarnish, which is not true actually because its surface is not that stable on the long term. 

Ultraviolet stability for outdoor use can be improved by opaque pigments that reflect the UV light before it can penetrate the polymer titanium dioxide and aluminum flake are frequently used for this purpose. Ultraviolet absorbers (UVAs) such as hydroxybenzotriaz-oles and hydroxybenzophenones are sometimes used, and hindered amine light stabilizers (HALS) are becoming more popular. 

Ultraviolet Light Stabilization. UV light stabilization is produced by fillers that reflect UV, particularly aluminum flake and Ti02, and by fillers that absorb UV radiation and reduce it to harmless wavelengths, particularly carbon black and zinc oxide (Sec. 5.1.4). 

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