Glass Paint Chills Metal in the Sun

Imagine you’re back in elementary school. Upon hearing the recess bell, you leave your pencils and books, and rush outside to the alluring glint of the playground in the sunlight. You ascend the slide’s steps, but hesitate. You touch the metal surface and pull back immediately. The metal is overwhelmingly hot from sunlight exposure.

Rest assured inner child, because scientists from Johns Hopkins Univ. have developed glass paint capable of protecting buildings, naval ships and, yes, even playground equipment from brutal sun rays.

“With sunlight, you think of UV (ultraviolet) degradation and those types of things, but one of the things that I think people forget is that just the heating itself can cause a lot of damage,” said Jason J. Benkoski, of the university’s Applied Physics Laboratory. Think about “corrosion, for example. If you put corrosion inhibitors in your paint, in order to protect steel or aluminum, you’ll be happy if you can decrease the rate of corrosion by a factor of 10.”

However, direct sunlight is capable of raising surface temperatures by 30 or 40 C, which increases corrosion by a factor of 16, according to Benkoski.



“Just by reflecting the sun’s light, and by passively radiating infrared light, you can actually do a lot of work, and, in fact, you can even cool” the ambient temperature, he said. “So if it’s an 80 (F) day outside, for example, you might have a 76 (F), or a 78 (F) surface just by…reflecting all the sunlight” and “radiating all your infrared light into outer space.”

And that’s exactly what Benkoski’s glass paint does. He presented his research at the 250th National Meeting & Exposition of the American Chemical Society.

To create the paint, Benkoski and his team strayed from polymer-based paints. Those paints, he said, degrade under UV light rays. Within two to three years, they may go from 90% reflective to 80%, he said.

“We’re actually using silica glass as our binder,” he said. “It’s almost like painting a rock on top of your surface.”

Specifically, the team used a modified version of potassium silicate. The changes allowed the compound to be water-insoluble when dry. Further, it has the capability to expand and contract with metal surfaces to prevent cracking.

It’s also fire resistant. “As it heats up, it actually expands into a foam,” said Benkoski. “That foam actually insulates the surface, and actually prevents the spread of the fire.”

Mixing zinc oxide pigment with the silicate gave the coating the ability to reflect sunlight, and passively radiate heat.

With pot ash and sand as starting points, the paint is cheap to make and the material abundant, Benkoski said. Being water-based, it gives off no volatile organics or greenhouse gases.

Funding for the research came from the U.S. Office of Naval Research. And the paint was developed for use as a topside coating for ships.