Purdue paints with record-breaking white

Out of West Lafayette, Indiana, Purdue University has earned a Guinness World Record for an unintended side effect to reducing global warming – creating the whitest paint ever.

"When we started this project about seven years ago, we had saving energy and fighting climate change in mind," said Xiulin Ruan, a professor of mechanical engineering at Purdue.

It was Ruan and a team of graduate students who invented the paint; the idea was to create a paint that would reflect sunlight away from a building.

Typical commercial white paint actually warms, rather than cools temperatures, as paints on the market are designed to reject heat reflection of only 80-90% of sunlight and cannot make surfaces cooler than their surroundings.

What makes the Purdue paint really reflective, is also what made it white. The formulation that Ruan's lab created reflects up to 98.1% of solar radiation at the same time as emitting infrared heat. Because the paint absorbs less heat from the Sun than it emits, a surface coated with this paint is cooled below the surrounding temperature without consuming energy.

Using this new paint formula to cover a roof area of about 1,000 square feet could result in a cooling power of nearly 10 kilowatts, Purdue researchers expressed in a published paper, "that's more powerful than the air conditioners used by most houses," Ruan noted.

This white paint is the result of research building on attempts going as far back as the 1970s to develop radiative cooling paint as a feasible alternative to traditional air conditioners. For the team, they had considered over 100 different materials and narrowed them down to 10, while also testing about 50 different formulations for each material.

The secret ingredient? Barium sulfate.

Two features that make this paint ultra-white: a very high concentration of a chemical compound of barium sulfate – a product of the critical mineral barite – and different particles sizes of the sulfate in the paint.

You can read more about barite and its various uses at Barite weighs in on critical minerals list in the Critical Minerals Alaska 2020 magazine.

What wavelength of sunlight each particle scatters depends on its size, so a wider range of particle size allows the paint to scatter more of the light spectrum from the Sun.

Currently, the research team has partnered with a company to scale up the paint for commercial distribution, while awaiting patent applications.

With a white paint that reflects nearly 100% of sunlight, and a black paint that absorbs practically the same, the world now has some high-tech contrasts that paint an ironically colorful tone as humankind continues to seek climate control techniques.