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'Smart' Glass Blocks Heat, Not Light

Photonics.com
Aug 2004
LONDON, Aug. 11 -- Researchers have developed an 'intelligent' window coating that, when applied to the glass of buildings or cars, reflects the sun’s heat so occupants don’t get too hot under the collar.

Although conventional tints block both heat and light, the coating -- which is made from a derivative of vanadium dioxide -- allows visible wavelengths of light through at all times but reflects infrared light when the temperature rises over 29 °C. Wavelengths of light in this region of the spectrum cause heating, so blocking infrared reduces unwanted rays from the sun. Soaring air conditioning bills or suffering in the sweltering heat could soon be a thing of the past, thanks to the University College London (UCL) chemists, who reported their finding recently in the Journal of Materials Chemistry.

The coating’s ability to switch between absorbing and reflecting light means occupants benefit from the sun’s heat in cooler conditions, but when temperatures soar room heating is reduced by up to 50 percent.

Ivan Parkin, a chemistry professor at UCL and senior author of the paper, said, "While the heat-reflective properties of vanadium dioxide are well recognized, the stumbling block has been the switching temperature. It’s not much good if the material starts to reflect infrared light at 70 °C. We’ve shown it’s possible to reduce the switching temperature to just above room temperature and manufacture it in a commercially viable way."

Troy Manning, lead author of the study and a chemistry professor based at the University of Liverpool, said, "For the glass manufacturing industry, one of the most important coating methods is atmospheric pressure chemical vapor deposition (APCVD), because it allows the film to be deposited during the float-glass manufacturing process and is performed at atmospheric pressure, so no high-cost vacuum systems are required. The films grow at such a fast rate, which makes the process ideally suited for such a high-throughput manufacturing process, and the glass comes off the production line already coated -- without the need for any additional processes. Other thin-film deposition processes -- such as physical vapour deposition and sol-gel spin coating -- are performed after the glass is made and require additional expensive equipment, such as vacuum systems for PVD or a spin-coater capable of holding large areas of glass."

The next step in getting the coating to market -- in about three years, the researchers predict -- is to investigate how durable it is. Another consideration is the color of the coating: "At present it’s yellow/green, which really isn’t attractive for windows," Parkin said. "So we’re now looking into color suppression as a way around this."

For more information, visit: www.ucl.ac.uk



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