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Metallic hydrogen, “holy grail of physics”

Scientists have just found a way to make metallic solid hydrogen in the lab, by compressing it at ultrahigh pressure between two diamond anvils. Credit: Ranga Dias; Isaac Silvera
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Almost a century after his theory, Harvard University scientists have succeeded in creating the rarest – and potentially one of the most valuable – material on the planet: atomic metallic hydrogen.

Created by natural science professor Isaac Silvera and postdoctoral researcher Ranga Dias, the material can help scientists answer fundamental questions about the nature of matter and can have a wide range of applications, such as being a superconductor at room temperature?

“This is the holy grail of high pressure physics. It is the first sample of metallic hydrogen on Earth, so when you are looking at it, you are looking at something that has never existed before,” Silvera describes in an article with details of Work that is published in ‘Science’. To create it, Silvera and Dias squeezed a small sample of hydrogen to 495 gigapascals, or more than 71.7 million pounds per square inch, a pressure greater than that of the center of the Earth.

At these extreme pressures, Silvera explains, the solid molecular hydrogen – which consists of molecules in web sites of the solid – breaks down and the tightly bound molecules dissociate to become atomic hydrogen, which is a metal. The work offers an important new window in understanding the general characteristics of hydrogen and offers tempting suggestions for new, potentially revolutionary materials.

“A prediction that is very important is that metallic hydrogen is predicted to be meta-stable,” Silvera says in a statement. “That means that if the pressure is removed, it will remain metallic, similar to the way it is formed Diamonds from graphite under intense heat and pressure, but it remains a diamond when pressure and heat are removed.”

Metallic hydrogen
Image Credit: http://www.sciencemag.org

In his view, understanding whether the material is stable is important because the predictions suggest that metallic hydrogen could act as a superconductor at room temperature. “That would be revolutionary,” he says. “15 percent of energy is lost through dissipation during transmission, so if you could wire this material and use it in the mains, it would be possible to change that story.”

Dias points out that among the holy grails of physics, a superconductor at room temperature could radically change our transport system, enabling the magnetic levitation of high-speed trains, as well as making electric cars more efficient and improving the performance of many electronic devices.

Metallic hydrogen use as a rocket propeller

The material could also provide significant improvements in the production and storage of energy: since superconductors have zero resistance energy, they could be stored by keeping the currents in superconducting coils and then used when necessary. Although it has the potential to transform life on Earth, hydrogen metal could also play a key role in helping humans explore the confines of space, such as the most powerful rocket propeller discovered.

“It takes a tremendous amount of energy to produce metallic hydrogen,” Silvera reveals, “and if you turn it back into molecular hydrogen, all that energy is released, making it the most powerful propellant on the rocket known to the Man, and could revolutionize space engineering. ”

The most powerful fuels in use today are characterized by a “specific impulse” – a measure, in seconds, of how fast a propeller is fired from the back of a rocket – 450 seconds. In comparison, it is theorized that the specific pulse for the metallic hydrogen is 1,700 seconds. “That would allow us to easily explore the outer planets,” Silvera says. “We would be able to put the rockets into orbit with only one stage in front of two and send larger payloads so it could be very important.”

To create the new material, Silvera and Dias resorted to one of Earth’s toughest materials: the diamond. But instead of natural diamond, the authors used two small pieces of carefully polished synthetic diamond which they then treated to make them even more resilient and then mounted opposite each other in a device known as a diamond anvil cell.

“Diamonds are polished with diamond dust and that can get the carbon off the surface,” Silvera says. “When we look at the diamond using atomic force microscopy, we find flaws that could make them weaken and break.” Thus, he points out that the solution was to use a reactive ion etching process to make a tiny sheet – just five microns thick, or about a tenth of a human hair – from the surface of the diamond.

The researchers then coated the diamonds with a thin layer of alumina to prevent hydrogen from diffusing into their crystalline structure and weakening them. After more than four decades of working on metallic hydrogen and almost a century after his first theory, seeing the material for the first time, Silvera recounts, “was exciting.”

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