Characterization and optimization of amorphous alumina-doped silica thin layer material of low emissivity coating technology for energy-saving applications

Abstract

Alumina-doped silica thin layers were synthesized through the sol–gel route and coatings on soda lime substrates. The alumina-doped silica films were reactively deposited from pure 97.5SiO₂–2.5Al₂O₃, 95SiO₂–5Al₂O₃, 90SiO₂–10Al₂O₃, and 85SiO₂–15Al₂O₃ mol.% targets. The densified xerogel were characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM) supplemented with EDS, and UV–vis spectroscopy (UVIS). The three crystalline phases andalusite (Al₂SiO₅), sillimanite (Al₂SiO₅), and silicon oxide (SiO₂) were identified as having an orthorhombic structure, as confirmed by XRD measurements. SEM characterization shows that the surface morphology of silica and alumina particles is composed of polygonal-shaped particles of non-uniform size. As the doping content of Al₂O₃ increases, the optical bandgap increases from 2.544 to 2.879 eV. Urbach energy(ΔE) and refractive index (n)were determined and lies within the range of 0.185 – 0.165 eV and 2.53 to 2.43, respectively. The increase of Al₂O₃ introduction led to the continuous increase of the tetrahedral proportion of [AlO₄] and strengthened the degree of glass network connection. Based on measured properties of all fabricated thin film glass samples, the sample code ASG4 (85SiO₂–15Al₂O₃ mol %) can be used for numerical simulation. Results indicate that the advanced thin layer coating can effectively reduce the solar heat gain and offer the possibility of significant energy savings in buildings.