Sodium Tungsten Bronze in Energy-Saving Glass

Tungsten bronze coatings and films have attracted global attention due to their application in near infrared (NIR) shielding windows. However, they are unstable in strong ultraviolet, damp heat, alkaline and/or oxidizing environment, and it is difficult to coat glass surfaces with complex shapes.

In order to overcome the disadvantages of tungsten bronze coatings, sodium tungsten bronze (NaxWO3) has been doped into bulk glasses using a simple glass melting method. Sodium tungsten bronze has been applied in energy-saving glass, the prepared glass is stable under hot, humid, oxidizing conditions, as well as under ambient conditions. The preparation process is as below:

First, the reduced tungsten oxide (WOx) is prepared by heating tungstic acid at 600 °C for 2 hours in a tube furnace at a flow rate of 400 mL·min-1 under a N2/H2 (95:5) atmosphere. The color of tungstic acid gradually changes from yellow to blue. The glass is prepared by a fusion quenching method. First, the raw materials WOx, NaF, H3BO3, SiO2 and Sb2O3 are uniformly mixed in the corundum crucible. The composition of WOx is adjusted to 6 mol%. Then. The mixture was melted at 1400°C for 2 hours. Subsequently, the melt is cooled to 1000 °C, and the melt is poured into a graphite mold for quenching at room temperature. After cooling and solidification, the resulting bulk glass was annealed at 450°C for 6 hours to remove internal stress.

In summary, sodium tungsten bronze has been applied in energy-saving glass, the prepared glass is stable under hot, humid, oxidizing conditions, as well as under ambient conditions. By changing the WOx concentration (2-8 mol%) and quenching temperature (1000-1400 °C), the NIR shielding performance of these glasses can be adjusted up to 100%. The new bulk glass has higher stability, simpler processing, and is easy to be made into complex shapes. It is an ideal substitute for energy-saving glass.

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