Researchers from Johns Hopkins University's Applied Physics Lab have developed an environmentally friendly glass paint that can both increase the lifespan and cool the surface of metal structures.
“Most paints you use on your car or house are based on polymers, which degrade in the ultraviolet light rays of the sun,” said lead researcher Jason J. Benkoski, Ph.D. “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.”
Direct sunlight is capable of raising surface temperatures by 30 or 40 degrees Celsius, which increases corrosion by a factor of 16. Just by reflecting the sun’s light, and by passively radiating infrared light, you can significantly reduce the damaging effects of the sun’s rays.
Traditional polymer-based paints degrade under UV light rays and, according to Benkowski, may go from 90 per cent reflective to 80 per cent in just two to three years.
Benkowski’s research team has used silica glass as the binder for their paint which he says is “almost like painting a rock on top of your surface.”
Using a modified version of potassium silicate, the changes allow the compound to be water-insoluble when dry and have the capability to expand and contract with metal surfaces to prevent cracking.
The solution is also fire resistant.
“As it heats up, it expands into a foam,” said Benkoski. “That foam then insulates the surface, and prevents the spread of the fire.”
Mixing zinc oxide pigment with the silicate gives the coating the ability to reflect sunlight and passively radiate heat. That’s key when it comes to protecting structures from the sun.
“When you raise the temperature of any material, any device, it almost always by definition ages much more quickly than it normally would,” Benkoski said. “It’s not uncommon for aluminum in direct sunlight to heat 70 degrees Fahrenheit 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.”
It is also extremely cost-effective and environmentally friendly. Potash and sand, which are the paint’s starting points, are naturally abundant. The water-based paint gives off no volatile organics or greenhouse gases.
Although development of the paint was originally intended for use on naval ships, Benkowski has identified 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 said. “It could even go on metal playground slides or bleachers.”
“A lot of that depends on people’s willingness to have a white roof though,” said Benkowski, admitting that in some areas, the prevailing architecture calls for terra cotta roofs.
“With our design, you can limit the heating by continuing to reflect ultraviolet and near infrared light, but there is an unavoidable heat penalty whenever you darken the visible colour.”
The biggest difference from existing commercial products is that the team is pushing for longevity.
“Ceramic coatings done right will outlast any polymer paint, but we have to overcome some of the inherent brittleness, porosity, and susceptibility to moisture. We hope to do so by adding just enough polymer additives to address these weaknesses without compromising the longevity that drew us to inorganic coatings in the first place,” said Benkowski.