Effect of acid, water and alcohol ratios on sol-gel preparation of antireflective amorphous SiO2 coatings

Preparation of Antireflective Silica Coating by the Sol-Gel Method for Heliothermic Power Plants

“…These silanol groups make the film surface polar and reactive, allowing interaction with water molecules physically adsorbed or bounded by hydrogen bonds 2,[9][10][11] . Fig.…”

“…[1][2][3][4] . To produce electricity, either in heliothermic power plants or photovoltaic systems, antireflective coatings play an important role reducing losses due to reflection of sunlight.…”

“…With the insertion of a porous coating layer it is possible to provide a more gradual transition of light from one medium to another, thus eliminating much of the reflection 6 . The absorber tube (Fig.1) Various materials and processes have been studied for obtaining antireflective surfaces, and silicon oxide (SiO 2 ) obtained by the sol-gel process is the one that provides the best results of reflectance [1][2][3][4][5] . In the sol-gel process is a transition occurs from a sol system to a gel system through the establishment of connections between colloidal particles or polymeric chains with the formation of a three-dimensional solid network 8 .…”

“…Thus, it is possible to have a precise control over the film microstructure, such as surface area, volume and pore size 1,8,11 . The low reflectance of the silica film obtained by the sol-gel process is a result of the porous structure formed during the film deposition; it makes the layer's refractive index achieve sufficiently low values reaching up to zero reflection of light by the surface, for a single wavelength [1][2][3]5 . Different techniques can be employed in production of antireflective films, such as dip-coating, sputtering and spin-coating.…”

“…Different techniques can be employed in production of antireflective films, such as dip-coating, sputtering and spin-coating. Among these the dip-coating technique is the most indicated and used to produce antireflective coatings by sol-gel process, especially when it is required the coverage of large areas or materials with complex shapes, furthermore it has low cost of deployment and operation if compared to the others techniques [2][3]5,9,12,13 . The Federal Center for Technological Education of Minas Gerais (Cefet-MG) was the first in Brazil to develop a project for the creation and operation of a heliothermic power plant.…”