The whitest paint in the world reflects 98.1% of the light. Could help in the climate fight

A new formula for white paint has given us the whitest white yet. It reflects a staggering 98.1 percent of all light that hits it, staying significantly cooler than room temperature, even when sitting in full sun.

If used to coat buildings, its inventors say, the paint could help in the fight against global warming by reducing our dependence on electric air conditioning, a habit that is making the climate crisis worse.

“If you used this paint to cover a ceiling area of ​​approximately 1,000 square feet [92.9 square meters], we estimate that it could get a cooling power of 10 kilowatts, “said mechanical engineer Xiulin Ruan from Purdue University.

“That is more powerful than the central air conditioners used by most houses.”

The team’s work is based on the paint they developed last year, which achieved a record reflection rate of 95.5 percent. The new formula, the team said, brings it that much closer to being a true counterpart to Vantablack, the black pigment that absorbs up to 99.965 percent of visible light.

The image below, with optical light on the left and infrared light on the right, shows how much cooler the painted surface is than the surrounding surface.

white paint insert(Purdue University / Joseph Peoples)

Vantablack has its own applications, but engineers and materials scientists have been chasing an ultra-reflective white paint for a while, for its potential cooling capabilities. Reflective cooling paints are already commercially available, like titanium dioxide paint, but they cannot reach temperatures colder than their surroundings.

To develop their new paint, the researchers looked for highly reflective white materials. His earlier painting was made from particles of calcium carbonate, the chemical compound found in chalk, limestone, and marble, suspended in an acrylic paint medium.

For their new formula, they turned to barium sulfate, which occurs naturally as the mineral barite and is commonly used as a pigment in white paint.

“We look at various commercial products, basically anything that’s white,” said mechanical engineer Xiangyu Li of the Massachusetts Institute of Technology, formerly at Purdue.

“We found that by using barium sulfate, you can theoretically make things really, really reflective, which means they’re really, really white.”

The trick is in the size and concentration of the particles. A range of different barium sulfate particle sizes allows the paint to disperse the maximum amount of light, and of course the more barium sulfate there is, the more light it can reflect. However, there is a point where too much barium sulfate can compromise the integrity of the paint, making it brittle and flaky when it dries.

The sweet spot, the researchers found, is a concentration of about 60 percent barium sulfate in the acrylic medium.

Xiulin RuanXiulin Ruan holding a painting sample. (Purdue University / Jared Pike)

During field tests, the team found that its painted surface managed to stay consistently cooler than room temperature by at least 4.5 degrees Celsius, achieving an average cooling power of 117 watts per square meter. He even kept this in the dead of winter.

For comparison, the equipment’s calcium carbonate paint had a surface temperature of more than 1.7 degrees Celsius below room temperature at noon and a cooling power of 37 watts per square meter, so the small Additional percent reflectivity in the barium sulfate paint made a significant difference.

Due to material limitations, barium sulfate paint probably cannot get much more Thoughtful, but what the team has accomplished could change the world for the better.

Air conditioning injects heat into Earth’s atmosphere in multiple ways, including pushing hot air out of buildings, heat from running machines, and the electricity generated by fossil fuels that powers them and contributes to emissions. of carbon dioxide.

Scientists have been searching for a passive radiative cooling method since the 1970s. This barium sulfate paint works, is reliable, and can be produced commercially quite easily. The team has filed a patent and hopes that the paint will soon become common use.

And then? Maybe we should license it for all but one artist to use.

The research has been published in ACS applied materials and interfaces.


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