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Monday, August 26, 2013
How Does Hydrogen Metallize?
The truth is that we do
not know at all and are still trying. That
is good enough though as it certainly generates upper limits. Those following this blog know that we can
expect to eventually model the content of such an atom and then possibly massage
it with external fields. Then who knows
what we will end up with?
We are also pushing
fundamental limits I am sure so our theory that we are working against may
simply be wrong.
All good stuff.
How does hydrogen
by Staff Writers
Washington DC (SPX) Aug 01, 2013
image shows the predicted optical absorption of a 1 um of hydrogen in a high
pressure diamond anvil cell for different crystal structures at a pressure of
300 GPa (3 million times normal atmosphere-similar to the pressure in the
center of the Earth). At these pressures hydrogen no longer forms molecules,
but instead forms in sheets, as shown in the figure. Scientists use optical
absorption to look for metallization in hydrogen, based on the assumption that
metallic hydrogen would be opaque as most metals are. But the team's analysis
shows that it may very well actually be transparent. Absorption units on the
graph (AU) are in factors of 10, meaning 2 AU lets just 1% of the incident
light pass through the structure (quite dark!). The graphite structure is an
ideal structure that is not expected to be observed in reality. The proposed
high-pressure forms, phase 3 (at low temperatures) and phase 4 (at room
temperature), are both predicted to be transparent in the near infrared and
optical frequencies of light, although phase 4 is poor metal. The Cmca
structure is a similar structure, but is predicted to be a better metal and
opaque, and to form at higher pressures. Graph is courtesy of Ronald Cohen.
Credit: Courtesy of Ronald Cohen, Carnegie Institution for Science.
is deceptively simple. It has only a single electron per atom, but it powers
the sun and forms the majority of the observed universe. As such, it is
naturally exposed to the entire range of pressures and temperatures available
in the whole cosmos. But researchers are still struggling to understand even
basic aspects of its various forms under high-pressure conditions.
difficulties contribute to the lack of knowledge about hydrogen's forms. The
containment of hydrogen at high pressures and the competition between its many
similar structures both play a part in the relative lack of knowledge.
high pressures, hydrogen is predicted to transform to a metal, which means it
conducts electricity. One of the prime goals of high pressure research, going
back to the 1930s, has been to achieve a metallic state in hydrogen. There have
been recent claims of hydrogen becoming metallic at room temperature, but they
work from a team at Carnegie's Geophysical Laboratory makes significant
additions to our understanding of this vital element's high-pressure behavior.
Their work is published in two papers by Proceedings of the National Academy of
Sciences and Physical Review B.
theoretical calculations from Carnegie's Ronald Cohen, Ivan Naumov and Russell
Hemley indicate that under high pressure, hydrogen takes on a series of
structures of layered honeycomb-like lattices, similar to graphite. According
to their predictions the layers, which are like the carbon sheets that form
graphene, make a very poor, transparent metal. As a result, its signature is
difficult to detect.
difficulty of detection means that the line between metal and non-metal in
hydrogen is probably blurrier than we'd previously supposed," Cohen said
"Our results will help experimental scientists test for metallic hydrogen
using advanced techniques involving the reflectivity of light."