Squashing Silane into Metal

Jan 09, 2009 by Kendra Snyder
Room-temperature infrared reflectivity spectra of SiH4 at selected pressures up to 67.2 GPa. The blue squares are the measurement results. The solid lines represent model fits to the data. The small gap in the spectrum near 2000 cm-1 is due to diamond anvil absorption.

(PhysOrg.com) -- Squeeze it hard enough and hydrogen, the most abundant and lightest element in our Universe, strangely takes on a metallic nature. During this state, as it loses hold of its electrons, hydrogen is believed to display unique characteristics including high-temperature superconductivity and properties that could be useful in developing new methods of energy production using nuclear fusion and alternative fuels. Creating this drastic phase change, however, is difficult, requiring extremely high temperatures and pressures.

As a result, efforts to actually form and detect solid metallic hydrogen have been elusive. Recently, though, a team of researchers from the Carnegie Institution of Washington, South China University of Technology, and the University of Western Ontario, used the NSLS to study silane, a hydrogen-rich compound, to learn more about the leader of the period table.

“Recent studies have suggested that the metallization pressure of group IVa hydrides like methane, silane, and germane might not be not as high as it is for pure hydrogen,” said Xiaojia Chen, a physicist at the Carnegie Institution of Washington and South China University of Technology. “We thought silane would be good system to study in order to get a look at this phase transition at a pressure at which it’s easier to confirm the material’s changes.”

Most scientists believe that the recipe for creating metallic hydrogen involves heating it to 3000 degrees Kelvin (a little hotter than 2,700 degrees Celsius) and exposing it to about 1.4 million atmospheres of pressure (140 GPa). By comparison, the pressure inside the core of the Earth is 380 GPa. These conditions, however, are very difficult to reach and record in a laboratory.

Using two silane samples, the researchers found far less demanding pressure requirements for metallization: about 60 GPa. Their experiment offers the first example for the metallization of an IVa hydride. Members of this periodic group contain hydrogen that is already compressed in naturally occurring compounds.

In order to conduct the experiment, the researchers placed their silane samples in a special apparatus called a diamond anvil cell, a device that uses the polished faces of two diamonds to apply extremely high pressure. By applying a range of pressures and measuring the results through infrared reflectivity experiments at beamline U2A, the group found that silane undergoes three phase transitions before becoming opaque at 27-30 GPa. Above 60 GPa, the material shows an increase in reflectivity, indicating pressure-induced metallization.

Their results were published in the January 8, 2008 edition of the Proceedings of the National Academy of Sciences and confirmed by a group using electronic resistance measurements later that year.

Next, the researchers want to investigate the pressure dependence of the superconducting transition temperature of metallic silane and its structure at high pressure. They also hope to study the properties of another compound, germane, which is predicted to switch to a metallic state at even lower pressures than silane.

“There’s great interest in these materials in terms of energy applications and in trying to better understand many planets,” Chen said. “Some planets are mostly made of hydrogen in a very pressurized state just like what we make at the synchrotron. Understanding how this element functions in such an extreme condition could have a wide variety of implications.”

Other authors involved in the study include Muhtar Ahart, Alexander Goncharov, Russell Hemley, Zhenxian Liu, Ho-kwang Mao, and Viktor V. Struzhkin, all from the Carnegie Institution of Washington, and Yang Song, from Carnegie and the University of Western Ontario.

Publication: X. Chen, V. Struzhkin, Y. Song, A. Goncharov, M. Ahart, Z. Liu, H. Mao, R. Hemley, "Pressure-Induced Metallization of Silane", Proc Natl Acad Sci, 105(1), 20-23 (2008).

Provided by NSLS

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User comments : 12

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5 / 5 (1) Jan 10, 2009
sweet so lets squeeze a bunch together and make us a new spaceship :)
not rated yet Jan 10, 2009
it's much easier to squeeze a free electrons, then some poor silane..

not rated yet Jan 10, 2009
I think I remember an astronomy prof. saying that hydrogen near Jupiter's center is so condensed that it akes on metallic properties. Then he blew up a soda can for some reason. anyway, we could probably learn more about how mettalic hydrogen behaves in nature if we build a telescope that can get a lot of data from under all those clouds.
not rated yet Jan 10, 2009
You cannot watch the metallic hydrogen by using of telescopes so easily, just because its formation requres a thick layer of nonmetallic hydrogen to compress it. In these experiment the thick layer hydrogen clouds was just replaced by thin and transparent layer of diamond anvil to be observed easier.
not rated yet Jan 10, 2009
Ignoring the financial issues, i don't see any reason why we couldn't send a little sattelite to go snoop around Jupiter.
not rated yet Jan 11, 2009
You should dive such sattelite a few thousands of kilometers beneath Jupiter surface to study metallic hydrogen directly. And you cannot change conditions indirectly during this. You cannot measure spectra and NMR and neutron scattering.., etc.
not rated yet Jan 11, 2009
Diving a satellite into Jupiter's mass of turbulent gasses is a bad idea. What we could do is have probe device. Something very small, yet very durable. It could go down, take measurements and recordings directly, and then report back to the satellite. The sattelite would then beam all the information back to us on Earth, NASA would throw a little party and everyone would go home happy.
not rated yet Jan 11, 2009
Silane experiments are motivated by preparation of room temperature superconductors, i.e. by much more practical target, then the understanding of Jupiter atmosphere.
not rated yet Jan 11, 2009
Well, I think it would be beneficial to see how it acts in nature. Of course, I'm a geek who gets all giddy inside whenever we send things to space and even more excited when we discover stuff in space. I'm a little biased toward exploring Jupiter a little more.
not rated yet Jan 12, 2009
Probes have been sent and dropped into Jupiter. The Galileo spacecraft studied the Jupiter system and dropped a probe into Jupiter before being de-orbited into Jupiter. The first link is to the wikipedia article about the Galileo mission, the second is to a graphic about the descent of the probe.



Of course, it would be nice to send a probe that could withstand extreme pressure. However, high-pressure probes (specifically, the materials necessary to withstand high pressure) tend to weigh a lot. Since a heavy spacecraft costs a lot to launch, it seems like a lot of money to spend on a piece of a spacecraft that is inevitably going to burn up after at most a few hours of data taking (assuming all goes well.)
not rated yet Jan 14, 2009
Jupiter, ha! Is anyone here thinking about that fat ball of fire in the sky? Yeah the sun, the core of that beast probably easily soars into tetrapascals and don't get me started of temerature. Does this mean our sun has a metallic core? Or am I so stupid that this is already in textbooks.
not rated yet Jan 16, 2009
Jupiter, ha! Is anyone here thinking about that fat ball of fire in the sky? Yeah the sun, the core of that beast probably easily soars into tetrapascals and don't get me started of temerature. Does this mean our sun has a metallic core? Or am I so stupid that this is already in textbooks.

The sun is too hot for a solid metal core. But, since the sun is mostly made up of hydrogen,which is a metal, i suppsoe the sun is in fact mostly metal.