Influence of sol–gel application conditions on metallic substrate for optical applications

Abstract

An efficient energy management of a building requires optimum use of the light energy, which is strongly dependent on optical properties of used materials. In the lighting sector, aluminium is generally employed as substrate for the reflectors. Nowadays, new steel substrates combining good corrosion resistance and flexibility are developed to answer the growing need of this market. Specific requirements for optical applications are a high reflectivity (total reflectivity >82%), a high superficial hardness and durability and also a suitable formability. The sol–gel layer is used in this particular application for its levelling properties before depositing of the reflective layer and good barrier properties to avoid contact between the metallic layers. The corrosion protection and the barrier properties of the sol–gel layer are investigated as a function of the thickness. The protection conferred by the sol–gel layer on stainless steel substrate is studied by the electrochemical measurements in a sodium chloride solution (electrochemical impedance spectroscopy and polarisation curves). The stress generated in the layer is determined versus temperature, humidity and hygrothermal conditions.