Influence of glass matrix SiO2-B2O3-NaF on the formation of NIR-shielding functional units in energy-saving window glasses

This work presents the influence of glass matrix SiO2-B2O3-NaF on the formation of near-infrared (NIR)-shielding functional units in energy-saving glass windows. The structural analyses by XRD, XPS, and Raman confirmed that the NIR-shielding performance is insensitive to SiO2 or B2O3 glass network formers but is significantly impacted by the concentration of NaF. This is because the presence of a reasonable amount of NaF provides the much-needed sodium for the formation of NIR-shielding functional units Na5W14O44 but too much NaF (>22 mol.%) can inhibit the formation of Na5W14O44 by transforming the W-O-W chain in the inter-connected [WO6] and [WO4] polyhedrons into W-O- bonds. By adjusting NaF to the optimal level (16 mol.%) and adding only a small amount of H2WO4 (1.9 mol.%) as the tungsten source in the raw materials, excellent optical properties and thermal insulation performance have been achieved in the produced bulk glass, with a high transmission of 65.8% at 550 nm in the visible light region and a low transmission of 6.6% at 1550 nm in the NIR region. This performance is much better than soda lime glass and ITO glass and is comparable to cesium tungsten bronze-based membrane coated glass. This study paves a way for glass composition design to achieve high NIR-shielding performance with the minimum amount of tungsten source, leading to cost-effective glass fabrication and enhanced mechanical strength of energy-saving glass windows.

Automated summary

This study investigates the influence of NaF concentration on the formation of near-infrared (NIR)-shielding functional units in glass windows. The results show that an optimal level of NaF concentration can enhance the NIR-shielding performance, while excessive NaF inhibits the formation of the functional units. By adjusting the NaF concentration and adding a small amount of H2WO4 as the tungsten source, glass with excellent optical and thermal insulation properties can be produced.