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Scientists Watch As Heat Moves Through 'Pencil Lead' at the Speed ​​of Sound



Scientists have seen something magical happening inside graphite: Heat is not expected to move like a wave – it usually diffuses and bounces off jiggling molecules in every direction; Whenever there is a wave, it can move in one direction in the crowd away from its source. Some day, this heat-transfer behavior in graphite could be down to microelectronics in a snap. That is, if they are working in a bone-chilling temperature of minus 240 degrees Fahrenheit, or minus 151 degrees Celsius.)

"If it makes to room temperature in some materials, Keith Nelson, study researcher at MIT chemist, told Live Science, adding that this is the highest temperature anyone has seen. [The 1

8 Biggest Unsolved Mysteries in Physics]

The researchers described "normal" heat movement using a heated kettle – after turning off the burner the process. These molecules bounce around in every direction; some of these molecules scatter right back to the kettle.

In solids, molecules do not move because of the atoms are locked into position. Chen, a mechanical engineer at MIT.

Rather, he said: "The thing that can move is sound waves," said Nelson, who spoke with Live Science along with co-author. the phonons can bounce and scatter, carrying heat. [What’s That Noise? 11 Strange and Mysterious Sounds on Earth]

Previously, the work by Chen predicted that a wave would move through graphite or graphene. To test this out, the MIT researchers crossed two laser beams on the surface of their graphite, creating what is called an interference pattern in which there were parallel lines of light and no light. This created the same pattern of heated and unheated regions at the graphite surface. Then, they aim at the laser beam at the setup.

"Normally, the heat would gradually diffuse from the heated regions to the unheated regions, until the temperature pattern was washed away," Nelson said. "Instead, the heat flowed from heated to unheated regions, and kept flowing even after the temperature was equalized everywhere, so the unheated regions were actually warmer than the originally heated regions." The heated regions, meanwhile, became even cooler than the unheated regions. And it all happened breathakingly fast – at about the same speed. [8 Ways You Can See Einstein’s Theory of Relativity in Real Life]

"Nelson told Live Science."

"How did they do this weird behavior?" to occur in graphite?

"From a fundamental perspective, this is just not ordinary behavior understand and explain it, "Nelson said.

Here's what they think is going on: Graphite, or a 3D material, has a layered structure in which the thin carbon layers are scarce, and so they sort of behave like graphene, which is a 2D material. Because of what Nelson calls this "low dimensionality," the phonons carrying the heat in one layer of the graphite are much less likely to bounce over and scatter off other layers. So, the phonons that can form in graphite have that's mostly too big to reflect backwards after crashing into atoms in the lattice, a phenomenon known as backscatter. These studies are published in the journal Science.

Editor's Note: This article was updated to clarify some of the methods in the experiment and the fact that the heat traveled at about the same speed that would sound through graphite, not air.

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