Metallic hydrogen

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The four gas planets of the solar system. Metallic hydrogen is assumed around the core.

As metallic hydrogen , a is high-pressure modification of hydrogen , respectively. Its existence was predicted theoretically and has so far only been proven at very high pressures and temperatures.

It is believed that metallic hydrogen occurs inside gas planets like Jupiter . It should - mixed with helium  - form a layer around the core of unknown composition; a coat of molecular hydrogen should then follow further out.

Basics

The metallic state is characterized by the fact that the outermost electrons of an element - these are precisely those that are also responsible for the chemical bonds - are in the elementary state in the conduction band . Since with hydrogen - in contrast to all other elements - there is only one single electron per atom , the incorporation of this electron into the conduction band would have to result in a lattice of atomic nuclei ( protons ) being created with a distance from each other due to the lack of internal ones Electrons may be much smaller than the Bohr radius , comparable to an electron wavelength (see also matter wave ).

hypothesis

Although the Periodic Table of the Elements is led by a column with alkali metals , hydrogen is not itself an alkali metal under ordinary conditions. In 1935, however, Eugene Wigner predicted the possibility that the hydrogen atoms would behave like the rest of the elements of the first main group under extreme pressure and give up their sole possession of their electrons, i.e. In other words , the electrons would stay in the conduction band and thus behave like in a metallic conductor .

exploration

The extremely high pressure required made experimental confirmation impossible for a long time. In March 1996, ST Weir, AC Mitchell, and WJ Nellis of the Lawrence Livermore National Laboratory first reported that they had produced metallic hydrogen for about a  microsecond at several thousand Kelvin and pressures greater than 10 11  Pascals (i.e. 100 GPa or one million  bar ) , identifiable by a strong decrease in electrical resistance . This was the first time a sixty year long search was successful. To do this , they used shock waves that condensed liquid hydrogen and deuterium very strongly for a short time and heated them up in the process. At the same time it was shown that the conductivity is strongly temperature dependent. At a temperature of 3000 Kelvin, the transition pressure to the metallic phase is around 140 GPa.

In 2011, researchers from the Max Planck Institute for Chemistry reported that they had converted hydrogen into a semiconductor state at 25 ° C and 2.2 megabars (220 GPa) pressure and converted it into a metallic state when the pressure was increased to 2.7 megabars.

Since hydrogen is not dissociated at lower temperatures , it is more difficult to achieve a phase transition into a metallic modification and significantly higher pressures are required. In January 2017, Ranga P. Dias and Isaac F. Silvera reported in the scientific journal Science that they had detected metallic hydrogen in a diamond press at temperatures of −268 ° C (5 K) and 495 GPa due to the increased reflection of the sample. The previously transparent sample initially darkened from 335 GPa and finally reflected more than 90% of the incident light at 495 GPa, which is typical for metals. Other scientists described the published results as not convincing. It has been criticized that the published results were based on a single experiment; other possible causes for the observations have not been adequately investigated.

If, on the other hand, hydrogen is in a Rydberg state , based on the measured bond length of 150 pm, it is assumed that no molecules are formed, but a metal lattice .

Applications

Metallic hydrogen could remain stable even without permanent pressure and freezing. Use as a superconductor at room temperature would therefore be conceivable.

One method for nuclear fusion is to aim a laser beam at pellets made of hydrogen isotopes . The increasing understanding of the behavior of hydrogen under extreme conditions can help to increase the energy yield.

Individual evidence

  1. ^ Fran Bagenal , Timothy Edward Dowling, William B. McKinnon: Jupiter: the planet, satellites and magnetosphere. Volume 1, Cambridge University Press, 2004, ISBN 978-0-521-81808-7 .
  2. ^ E. Wigner, HB Huntington: On the Possibility of a Metallic Modification of Hydrogen. In: J. Chem. Phys. 1935, 3, pp. 764-770, doi : 10.1063 / 1.1749590 .
  3. ^ ST Weir, AC Mitchell, WJ Nellis: Metallization of Fluid Molecular Hydrogen at 140 GPa (1.4 Mbar). In: Phys. Rev. Lett. 1996, 76, pp. 1860-1863, doi : 10.1103 / PhysRevLett.76.1860 .
  4. ↑ Max Planck Institute for Chemistry: High pressure makes hydrogen metallic. November 17, 2011, accessed November 18, 2011.
  5. ^ Ranga P. Dias, Isaac F. Silvera: Observation of the Wigner-Huntington transition to metallic hydrogen . In: Science . 2017, doi : 10.1126 / science.aal1579 .
  6. ↑ a b World of Physics: When hydrogen becomes metal. January 26, 2017. Retrieved January 27, 2017.
  7. ^ Davide Castelvecchi. Physicists doubt bold report of metallic hydrogen , Nature , January 26, 2017.
  8. ↑ Shahriar Badiei, Leif Holmlid: Experimental observation of an atomic hydrogen material with H – H bond distance of 150 pm suggesting metallic hydrogen. In: J. Phys. Condens. Matter. 2004, 16, pp. 7017-7023, doi : 10.1088 / 0953-8984 / 16/39/034 .
  9. ↑ GSI Helmholtz Center for Heavy Ion Research : The other way to nuclear fusion. ( Memento of March 11, 2012 in the Internet Archive ). August 11, 2003, accessed November 27, 2009.