Metallic hydrogen

Metallic hydrogen is called a high-pressure modification of hydrogen. Its existence was predicted theoretically and has so far been detected only at very high temperatures.

It is believed that metallic hydrogen occurs in the interior of giant planets such as Jupiter. He forms - mixed with helium - a layer around the core of unknown composition. Further out, followed by a coat of molecular hydrogen.

Basics

The metallic state is characterized by the fact that the outermost electrons of an element - these are precisely the ones that are responsible for the chemical bonds - are located in the elemental state in the conduction band. Since the hydrogen - in contrast to all the other elements - is only one electron per atom, the installation of this electron in the conduction band would have to lead to a lattice of atomic nuclei (protons) produced at a distance from each other, which due to non-existent internal electron may be much smaller than the Bohr radius, compared to a wavelength of electrons (see matter wave ).

Forecast

Although the periodic table of elements is led by a column of alkali metals, alkali metal hydrogen itself is not under ordinary conditions. However, Eugene Wigner said in 1935 on the assumption that the hydrogen atoms would behave under extreme pressure as the remaining elements of the first main group and would give up their sole ownership of their electrons. That is, the electrons would be in the " conduction band " and thus behave like a metallic conductor.

Research

The extremely high pressure required did an experimental confirmation for a long time impossible. In March 1996, ST Weir, AC Mitchell and WJ Nellis reported by the Lawrence Livermore National Laboratory that it for about a microsecond of several thousand Kelvin and pressures in excess of 1011 pascals ( ie 100 GPa and a million bar ) the first have produced metallic hydrogen, identifiable by a strong decrease of the electrical resistance. This was a sixty- year quest for the first time successfully. They used shock waves for a short time compressed liquid hydrogen and deuterium very strong and it also heated the. At the same time it was found that the conductivity is strongly temperature dependent. At a temperature of 3000 Kelvin the transfer pressure to the metal phase is about 140 GPa.

Researchers at the Max Planck Institute for Chemistry report, at 25 ° C and 2.2 megabar to have brought (220 GPa) pressure hydrogen in a semiconductor state and the pressure continues to increase to 2.7 megabar to a metallic state.

Hydrogen is not present as dissociated at lower temperatures, it is more difficult for these to obtain a phase change in a metal modification and requires much higher pressures. Therefore, so far could not be experimentally produced metallic hydrogen at low temperatures. At pressures up to 342 GPa no evidence of metallic hydrogen could be found. It will be assumed conversion pressures of about 450 GPa.

Is hydrogen on the other hand in a Rydberg state before, it will be presumed on the basis of the measured bond length of 150 pm, that it is a metallic 3D structure and no molecules.

Applications

A method for nuclear fusion is to direct a laser beam on pellets of hydrogen isotopes. The increasing understanding of the behavior of hydrogen under extreme conditions can help to increase the energy yield.