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

Abstract

This work deals with the deposition of a thin layer of porous silica antireflective coating onto glass substrates. The films were deposited with different withdrawal speeds and heat-treated at 425°C for 30 minutes. The effects of heat treatment and film deposition rate on the films reflectance were evaluated. The diffuse reflectance was measured using ultraviolet-visible (UV-Vis) spectroscopy. Scanning electron microscopy (SEM) was used for microstructural evaluation of the films. The water contact angle upon the films surface was evaluated using a tensiometer and was based on the sessile drop technique. The mechanical characteristics of the films were evaluated by tape test and pencil hardness. The obtained sol-gel silica coatings were homogeneous and free of cracks. UV-Vis analysis of the glass substrate revealed a reflectance value of 3.86%, whereas the lowest reflectance value obtained for antireflective coatings was 2.72%. The contact angle measurement showed that, for all films, there was wetting of the film by water, characterizing them as hydrophilic. The adhesion of the films were 4B and the pencil hardness were 3H.

Preparation and Characterization of Some Sol-Gel Modified Silica Coatings Deposited on Polyvinyl Chloride (PVC) Substrates

“…This coating has hydrophilic property because the forces of interaction between water and the substrate are nearly equal with the cohesive forces of bulk water, and water does not cleanly drain from the substrate. The contact angle decrease due to the not stable siloxane groups (Si-O-Si) or to the presence of free silanols groups (Si-OH) that make the film surface polar and reactive, allowing interaction with water molecules physically adsorbed or bounded by hydrogen bonds [36].…”

Production and Characterization of a Silica-Alumina Membrane Using Novel Tubular Freeze-Cast Substrates

“…The sol-gel route can be used for production of the separation layer, since it has been proven as an efficient method for production of high-quality silica membranes 22,23 . It allows precise control of the pore structure (shape and pore size distribution) 24,25,26 , a desired characteristic for membrane production. In addition, it is a suitable route for thin film deposition, due to the capability to coat materials of various shapes and areas, as well as demanding low temperatures and simple equipment 22,24,27 .…”

“…It allows precise control of the pore structure (shape and pore size distribution) 24,25,26 , a desired characteristic for membrane production. In addition, it is a suitable route for thin film deposition, due to the capability to coat materials of various shapes and areas, as well as demanding low temperatures and simple equipment 22,24,27 . For production of microporous Figure 1.…”

“…silica layer, acidic synthesis conditions and short aging times are preferred before deposition 25 . The use of dipcoating for production of sol-gel derived silica coatings has shown its capability to produce homogeneous layer 24,28 . According to the Landau-Levich equation 28 , the dip coating method allows control of the film thickness by adjusting the withdrawal speed 29 .…”