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Glass Coating Lets Sunshine in Without Too Much Heat

Science File

August 14, 2004|Eric D. Tytell | Times Staff Writer

A new glass coating made of vanadium dioxide could provide relief for sky-high summer air conditioning bills -- without affecting winter heating costs, according to a study in the latest Journal of Materials Chemistry.

Chemists from University College London covered glass with a thin layer of the compound mixed with a sprinkling of tungsten, a combination that blocks the sun's infrared rays when it's hot, but lets the sun's warmth through in the cold.

Ordinary glass tints block heat at all temperatures but also cut out visible light. The vanadium coating is transparent to visible light but reflects infrared at temperatures above 84 degrees, reducing solar heat by about 50%. Architects face a dilemma in buildings with a lot of glass, said Ivan Parkin, a coauthor of the study. "Do they tint the glass, which reduces the benefit of natural light, or face hefty air conditioning bills?"

Scientists have long known that vanadium dioxide, which has a yellow-green color, switches at a certain temperature from passing infrared light to blocking it. Until researchers added tungsten, though, the transition temperature was always too high. The team developed a method to mix vanadium dioxide with about 2% tungsten, lowering the transition temperature.

Troy Manning, the study's lead author, said a viable product could be available in about five years, though chemists would need to make the color more appealing.

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