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Glass-Based Coating to Protect Ships

Tuesday, August 18, 2015

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A researcher at Johns Hopkins University set out to develop an environmentally friendly coating to deflect the damaging heat and rays of the sun and prolong the life of metal structures.

What he came up with was an innovative coating made out of glass that can be used on metal surfaces in applications ranging from naval ships to rooftops.

Inspired by Glass

Jason J. Benkoski, Ph.D., senior scientist in the Johns Hopkins University Applied Physics Lab, chose to work with glass, which is made out of silica, for his ideal coating because it is hard, durable and has the right optical properties.

glass coating testing tiles
American Chemical Society

Benkoski's silica-based coating, for use on military ships and other metal surfaces, can expand and contract with fluctuating air temperatures, reflect sunlight and resist water.

He told Forbes magazine, his lab was inspired by the durability of paints known as “water glass.” “The starting materials are the cheapest things you can imagine—sand and potash,” he said.

The long-standing facades in Germany and Switzerland were given as an example of the exterior use of water glass paints—they likely have maintained their splendor over time because the glass reflected sunlight.

Water glass paints required a clean rough surface to cling to, though, which doesn’t make them a good match for metal, Benkoski explained. 

At Work in the Lab

In the lab, Benkoski began with silica, one of the most abundant materials in the Earth’s crust, and modified one version of it, potassium silicate, that normally dissolves in water. His tweaks transformed the compound so that when it’s sprayed onto a surface and dries, it becomes water resistant.

Benkoski explained the logic behind his research: “Most paints you use on your car or house are based on polymers, which degrade in the ultraviolet light rays of the sun. 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,” he said in a release from the American Chemical Society.

Benkoski reflectance testing
American Chemical Society

This silica-based coating is designed to keep an outdoor metal surface close to air temperature and thereby slow down corrosion and other types of degradation.

Unlike acrylic, polyurethane or epoxy paints, Benkoski’s paint is almost completely inorganic, which should make it last far longer than its counterparts that contain organic compounds, according to the ACS. 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. That’s key 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’s almost like painting a rock on top of your metal. And this is going to last not tens of years but maybe hundreds of years,” he said in National Geographic.

Applications in the Field

The paint Benkoski’s lab is developing is intended for use on naval ships (some funding for his work was provided by the U.S. Office of Naval Research), but it has other potential commercial applications, including as a cool roof coating.

“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.

“White paint by itself does a good job,” reflecting about 90 percent of the sun’s energy, he told National Geographic.

But, he explained, a polymer-based coating cannot reject ultraviolet light like a silica-based paint can. “With as little as three years of UV degradation, a polymer paint could absorb twice as much solar energy as it did when freshly painted,” he added.

Mixing pigments with the silicate gives the coating the ability to reflect sunlight and passively radiate heat.

He suggested the paint could also go on metal playground slides or bleachers. And it would be affordable. The materials needed to make the coating are abundant and inexpensive.

He indicated he also expects to find applications for ceramics such as glass, concrete and rock, as well as fiberglass or previously polymer-painted surfaces.

Development Schedule

Not yet on the market, Benkoski says he expects his lab will start field testing the material in about two years.

He told National Geographic it could take five years for the product to reach the commercial market, and he expects the paint’s chances for success will be bolstered by the Navy’s sponsorship of his research.

Benkoski presented his work at the 250th National Meeting & Exposition of the American Chemical Society (ACS) on Sunday (Aug. 16). ACS, the world’s largest scientific society, is holding the meeting in Boston through Thursday (Aug. 20).

   

Tagged categories: Asia Pacific; Coating chemistry; Coating Materials; Coatings Technology; Cool roof coatings; Corrosion resistance; EMEA (Europe, Middle East and Africa); Laboratory testing; Latin America; North America; Protective Coatings; Reflectance; Reflective coatings; Reflective roof coatings; Research and development; Solar reflectance

Comment from Joseph Brackin, (8/18/2015, 9:28 AM)

Anyone looked at the health issues associated with blasting of this product (silica)? from a Naval perspective, that could be a showstopper.


Comment from M. Halliwell, (8/18/2015, 12:44 PM)

Interesting point, Joseph. I guess it depends on how this product ends up...if it is a bit more vitrified, I would think it should be like using glass beads for blasting. If it reacts more like a sand, then that could be an issue.


Comment from peter gibson, (8/18/2015, 1:30 PM)

He says it lasts 50 years....no need to blast.not an issue.


Comment from M. Halliwell, (8/19/2015, 10:29 AM)

Hehehe...true Peter, but I'm going to assume that means with proper application. I think we have all seen examples where someone's coating job wasn't applied quite to spec or under less than ideal circumstances. If a 10 year coating won't last 2 due to the semi-trained monkey someone had apply it on the cheap in the first place, I think removing a failed glass-based coating still needs to be considered.


Comment from Tom Schwerdt, (8/19/2015, 10:42 AM)

I'm not clear from the article how this (potential) product is improved from the silicate paints used since the 1800s. The comparisons in the article are made against organic-binder paints. Silicate based paints have been used successfully on metal at least since the 1930s (inorganic zinc, Australia. Required baking) and air cured zinc silicate primers (inorganic zinc) been widely available since the 1970s.


Comment from john schultz, (8/20/2015, 8:28 AM)

It might be nice to see something like this replace the paint used now on appliances and architectural metals such as widow frames, balcony rails and so on. Focusing on the reflectance value is pretty narrow thinking.


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