Keeping metal structures cool with glass paint

Sunlight can wear down even the strongest structures. To fend off damage and heat from the sun's rays, scientists have developed an environmentally friendly paint out of glass that bounces sunlight off metal surfaces keeping them cool and durable.

"Most paints you use on your car or house are based on polymers, which degrade in the ultraviolet light rays of the sun," says Jason J. Benkoski, PhD. "So over time you'll have chalking and yellowing. Polymers also tend to give off volatile organic compounds, which can harm the environment. That's why I wanted to move away from traditional polymer coatings to inorganic glass ones."

Glass is hard, durable and has the right optical properties, but is very brittle. To address this, Benkoski, of the Johns Hopkins University Applied Physics Lab, started with silica, one of the most abundant materials in the earth's crust and one of the main compounds in glass. He modified one version of it, potassium silicate, which normally dissolves in water. His tweaks transformed the compound so that when it's sprayed onto a surface and dries, it becomes water resistant.

Unlike acrylic, polyurethane or epoxy paints, Benkoski's paint is almost completely inorganic, which he says should make it last far longer than its counterparts that contain organic compounds. His paint is also designed to expand and contract with metal surfaces to prevent cracking.

Mixing pigments with the silicate gives the coating an additional property: the ability to reflect all sunlight and passively radiate heat. Since it doesn't absorb sunlight, any surface coated with the paint will remain at air temperature, or even slightly cooler.

"When you raise the temperature of any material, any device, it almost always by definition ages much more quickly than it normally would," Benkoski says. "It's not uncommon for aluminium in direct sunlight to heat 21°C above ambient temperature. If you make a paint that can keep an outdoor surface close to air temperature, then you can slow down corrosion and other types of degradation."

The paint Benkoski's lab is developing is intended for use on naval ships. But it has many other potential commercial applications.

"You might want to paint something like this on your roof to keep heat out and lower your air conditioning bill in the summer," he says. The materials needed to make the coating are abundant and inexpensive meaning that the paint would be inexpensive, in theory.

Benkoski says he expects his lab will start field testing the material in about two years.

Author
Tom Austin-Morgan

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