Tungsten Bronze as Transparent Thermal Insulation Coating

In many countries' energy consumption, building energy consumption accounts for about 30-40% of national energy consumption, while energy lost through glass doors and windows accounts for more than 50% of building energy consumption. About 46% of the solar spectrum is near-infrared light. So, if the transmission of near-infrared light is reduced, electricity used for ventilation and cooling system would be cut down. Therefore, research and development of transparent thermal insulation coatings for energy efficient glass has important practical significance. It can be predicted that transparent thermal insulation coatings have considerable prospects due to their economical and energy-saving significance.

At present, the materials for preparing the transparent heat insulating coating mainly include: antimony tin oxide (ATO), indium tin oxide (ITO), LaB6, VO2, and alkali metal tungsten bronze (MxWO3). It is found that MxWO3 nanomaterials have strong near-infrared light shielding ability.

Some scholars have proposed a method for preparing variable-value tungsten bronze Ax-MyWO3 nano-short rod particles with excellent visible light transmission and near-infrared shielding performance. The processes are as following steps:

1) Weigh 6.3503g of sodium tungstate, add 30ml of deionized water, fully dissolve, and quickly add 5mol/L hydrochloric acid under stirring to make the pH ≤1. After stirring for 30min, we will get the yellow pigmented colloidal tungsten. The acid colloid suspension is filtered to obtain a milky yellow solid tungstic acid having a certain volume; the solid colloidal tungstic acid is added to 120 ml of deionized water, and the mixture is uniformly stirred under ultrasonic vibration assisting conditions to be redispersed into suspension. The solution was further filtered by suction, and repeated three times; the above operation was repeated using 120 ml of absolute ethanol, and the mixture was filtered three times. The obtained block gel was taken out and added with an appropriate amount of absolute ethanol to make a total volume of 77 ml, and stirred and dispersed under ultrasonic shaking conditions. Suspending liquid to obtain a solid colloidal tungstic acid ethanol dispersion;

2) Preparation of reaction precursor solution and powder synthesis

Weigh 0.6g of barium sulfate, add it to 40ml solid colloidal tungstic acid ethanol dispersion, measure and add 70ml of acetylacetone, add 8.356g of oxalic acid, 1g of P123 inducer, and finally add 0.198g of FeCl2•4H2O, stir 2h, the reaction precursor liquid was obtained; the reaction precursor liquid was transferred into a 200 ml autoclave, and the reaction was continuously carried out at 190 ° C for 72 hours. The precipitate after the reaction was washed with water and alcohol three times in sequence, and after centrifugation, at 60 ° C. After drying for 10 h, the synthesized powder was Fe-doped Fe0.1-Cs0.32WO3 hexagonal germanium tungsten bronze according to XRD and EDS.

The Cs0.32WO3 hexagonal germanium tungsten bronze nano-short rod particles synthesized by the above method have small particle size and high uniformity of particle size. The near-infrared shielding performance of the obtained powder before the heat treatment without hydrogen has been significantly better than the prior art, reaching nearly 90%; and after the hydrogen heat treatment, it will achieve higher near-infrared shielding performance (≥95%) and photothermal Conversion efficiency; The powder preprared has excellent photocatalytic degradation ability and can be widely used in photocatalytic degradation of pollutants. It can be applied as transparent thermal insulation coating for energy efficient glass, which saves the energy usage of the building’s ventilation and cooling system. Moreover, the preparation method has the advantages of mild reaction conditions, convenient industrial implementation and widespread promotion.

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