Most commercial white paints like light a little too much: they reflect between 80 and 90% of it, but end up, despite their immaculate efforts, absorbing the rest.
Still, the benefits of whiter-than-white are significant, especially when it comes to refreshment. As reported New Atlas in 2012scholarly calculations by NASA and Columbia showed that covering all the roofs of New York buildings with white would make it possible to lower their maximum temperature by 24°C, thus helping to curb the heat bubble phenomenon.
What if white rejected light even better? The effect, of course, would be even more interesting. Then comes the team of researcher Xiulin Ruan, from Purdue University: last year, they announced that they had succeeded in creating a paint capable of reflecting a record 98.1% of light, well beyond traditional commercial materials. .
An antithesis of the now famous Vantablack, the blackest black in the world, in a way. To do this, they put in their mixture du sulfate de bariuma common and inexpensive chemical compound, used in particular as a pigment in the field of paintbut also essential in that photographic development and the gelatin silver process.
Xiulin Ruan’s secret was the barium sulphate density of his preparation, and its atomic structure – a delicate arrangement of particles of varying sizes allowed the mixture to hold as well as a traditional paint.
In terms of air conditioning, the feat was notable –and then noted by New Atlas– and the conclusive tests: in real conditions, the Purdue team’s paint managed to lower the temperature of the covered surfaces by 5 to 10°C, day and night respectively.
The preparation of Ruan & co. nevertheless had a defect: to reach this extreme level of reflection, it had to be thick (400 microns). This was not unacceptable in the fields of construction and painting of buildings, but disqualified it in other fields where weight and thinness are crucial – the automobile or the aviation, for example.
The team therefore worked on a new preparation, based on the same principle as the first, but whose properties would make it thinner, lighter and more easily applicable to a Twingo, an A320 or a high-speed train.
Bingo: the new formula, based on boron nitride organized in “hexagonal nanoplatelets”, to use the terms of New Atlas, reflects 97.9% of the light with a layer of only 150 microns, and its lower density allows it to gain 80% in weight.
“The weight of this paint opens the door to a number of applicationsexplains George Chiu, professor at Purdue. This paint now has the potential to refresh the exterior of airplanes, automobiles or trains. A plane waiting on the tarmac on a hot summer day won’t need to run its air conditioning as loudly to stay cool, which saves a lot of energy. Spacecraft also need a lightness that they could find in this painting.