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If last year we were given the big news of the discovery of gravitational waves, 2017 might carry one that beats that by a large margin: the synthesis of metallic hydrogen
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"This is the holy grail of high-pressure physics. It's the first-ever sample of metallic hydrogen on Earth, so when you're looking at it, you're looking at something that's never existed before."
Prof. Isaac F. Silvera, Harvard University Department of Physics, 2017
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Hydrogen, as any materials scientist will tell you, is a tough nut to crack. It is the simplest of the atoms, but in its molecular, or solid state it is incredibly complex. The long-sought goal of turning the element into a metal, it has been predicted, would require pressure close to that found at the center of the planets.
The possibility of metallic hydrogen is of enormous importance because of the material's potential as a superconductor, conducting electricity with little or no resistance, resulting in huge energy savings. It is also believe the metal could be relevant to the study of the interiors of larger planets, such as Jupiter, where metallic hydrogen is thought to be in abundant supply. In the periodic table, hydrogen sits above the alkali elements such as lithium, sodium and potassium, which are all metals. Since the mid-1930s researchers have known that if sufficient pressure is applied to solid hydrogen, it, too, will become an alkali metal. |
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Hydrogen becomes a solid either at low temperatures or under compression. In this state, it is a good insulator, like rubber. As the pressure is increased, the solid will ultimately become a metal, and a conductor, like copper. The theoretical explanation of this is that as the hydrogen is squeezed, the molecule decomposes and forms a lattice of protons surrounded by electrons. But most previous theories have grossly underestimated the pressure required to do this.
Calculations suggest that depairing (destruction of the molecular bond) should occur around 340 GPa (A GPa is a gigapascal, a measurement of atmospheric pressure, and is equal to 10,000 times the pressure at the Earth's surface. The pressure at the center of the Earth is about 361 GPa, or more than four million times surface pressure.), accompanied by the formation of an alkali metal at this pressure or at substantially higher pressures. But the researchers found that solid hydrogen showed no signs of looking like a metal at pressures of up to 342 GPa.
Such incredible pressures were achieved by compressing the hydrogen in a diamond anvil cell, a small device consisting of pairs of the highest quality diamonds with tips beveled to one-fourth the diameter of a human hair. Previously material physicists have used diamond anvil cells to make metallic oxygen, sulfur and xenon. In 1998 researchers at Carnegie Institute in Washington, D.C., reproduced these experiments on metallic sulfur, but at low temperatures, and found that the material becomes a superconductor at 10 degrees Kelvin (minus 442 degrees Fahrenheit) when the metallization pressure is reached.
Applications
One technique of producing nuclear fusion, called inertial confinement fusion, involves targeting laser beams at pellets of hydrogen isotopes. The increased understanding of the behavior of hydrogen in extreme conditions might help to increase energy yields. If realized, this may solve the world’s energy needs once and for all.
It might also be possible to fabricate extensive quantities of metallic hydrogen for another practical purpose: fuel. It has been theorized that it might be possible to get hydrogen into a form called Meta-stable Metallic Hydrogen (MSMH), which would not immediately revert to ordinary hydrogen upon the release of pressure. A system is in a meta-stable state when it is in equilibrium (not changing with time). MSMH would make an efficient fuel itself and also a clean one, with only water as an end product.
Thus far we have only used liquid hydrogen in rockets, which is problematic due to the need to keep it at cryogenic temperatures, and the amount required limits the size of the rocket, and therefore the range of space exploration. A rocket fueled by metallic hydrogen will expand our reach, and make manned exploration of the solar system beyond the moon both possible and economical.
Calculations suggest that depairing (destruction of the molecular bond) should occur around 340 GPa (A GPa is a gigapascal, a measurement of atmospheric pressure, and is equal to 10,000 times the pressure at the Earth's surface. The pressure at the center of the Earth is about 361 GPa, or more than four million times surface pressure.), accompanied by the formation of an alkali metal at this pressure or at substantially higher pressures. But the researchers found that solid hydrogen showed no signs of looking like a metal at pressures of up to 342 GPa.
Such incredible pressures were achieved by compressing the hydrogen in a diamond anvil cell, a small device consisting of pairs of the highest quality diamonds with tips beveled to one-fourth the diameter of a human hair. Previously material physicists have used diamond anvil cells to make metallic oxygen, sulfur and xenon. In 1998 researchers at Carnegie Institute in Washington, D.C., reproduced these experiments on metallic sulfur, but at low temperatures, and found that the material becomes a superconductor at 10 degrees Kelvin (minus 442 degrees Fahrenheit) when the metallization pressure is reached.
Applications
One technique of producing nuclear fusion, called inertial confinement fusion, involves targeting laser beams at pellets of hydrogen isotopes. The increased understanding of the behavior of hydrogen in extreme conditions might help to increase energy yields. If realized, this may solve the world’s energy needs once and for all.
It might also be possible to fabricate extensive quantities of metallic hydrogen for another practical purpose: fuel. It has been theorized that it might be possible to get hydrogen into a form called Meta-stable Metallic Hydrogen (MSMH), which would not immediately revert to ordinary hydrogen upon the release of pressure. A system is in a meta-stable state when it is in equilibrium (not changing with time). MSMH would make an efficient fuel itself and also a clean one, with only water as an end product.
Thus far we have only used liquid hydrogen in rockets, which is problematic due to the need to keep it at cryogenic temperatures, and the amount required limits the size of the rocket, and therefore the range of space exploration. A rocket fueled by metallic hydrogen will expand our reach, and make manned exploration of the solar system beyond the moon both possible and economical.
Further readings
Metallic hydrogen, at Wikipedia
"A Breakthrough in High-Pressure Physics?" Harvard Magazine article on the discovery
"Metallic hydrogen finally made in lab at mind-boggling pressure", New Scientist article
Professor Isaac F. Silvera, the hero of the hour (and future Nobel laureate?)
