Metallic Hydrogen

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Politically, the world seems to be going to a very dark place. However, it is comforting to see that scientists continue to make incredible discoveries; science is a light in the darkness, providing hope for a better future.

One such discovery was made by scientists at Harvard University, who have been able to convert Hydrogen (normally a gas) into a solid metal.

The Theory

Hydrogen is the most simple element in the universe, and for that reason it was the first to come into being. It consists only of a large positive particle called a proton, orbited by a much smaller negative electron. Hydrogen rarely exists as a single atom – it almost always exists as a molecule of two Hydrogen atoms bonded together. This occurs when the electrons in the 2 Hydrogen atoms interact with eachother to form a bond, which is more stable than the electrons residing on one atom alone. This forms the molecule H2, which exists as a gas.

The researchers cooled down Hydrogen gas to very low temperatures under pressures of around 5 million times Earth’s atmosphere. This forces H2 molecules to come together, with the bonds between them breaking to form a clump of protons held together by a cloud of electrons – a metal. These kind of pressures are unheard of on our planet, but scientists think some metallic Hydrogen may exist within gas giant planets like Jupiter. If the scientists have made what they say they have, it would be the first metallic Hydrogen ever seen on Earth.

Metallic Hydrogen could exist in the gas giant Jupiter, but never before has it been seen on Earth. Image [Image Source: brianasaussy.com]
The transition from H2 to metallic Hydrogen imaged (top). Underneath is a schematic, showing how the H2 molecules may come together to form a metal at extreme pressures. [Taken from phys.org, credit: R. Dias and I.F. Silvera]
 

 

 

 

 

 

 

 

 

Why does this matter?

Metallic Hydrogen could have some revolutionary applications that could totally change technology. It is thought to be a superconductor at room temperature, meaning it can conduct electricity with virtually no resistance. All currently known superconductors only work at extremely low temperatures. Another suggested application is fuel: if metallic Hydrogen could convert rapidly back into gas, it would release enormous amounts of pressure – this could potentially be harnessed to power  spacecraft or produce electricity.

Should we get excited yet?

Such impressive claims are controversial, with many being critical of the research. First of all, only one tiny sample has been made, which may not be repeatable. It would also require further testing to prove its metallic nature.

[Image source: philosophyib.com]   

For Metallic Hydrogen to be useful, it would need to be metastable like diamond. As an aside, diamond is an example of a metastable substance. Both diamond and graphite are different arrangements of Carbon, graphite being more stable and much more common as a result. However, diamond takes millions of years to decompose into graphite. Over the time diamonds erode, new diamonds are made by the specific geological conditions in the Earth that favour them; some diamonds will always exist, but they will remain very rare. On human timescales therefore, diamonds are indeed forever. But nobody knows if this could apply to metallic Hydrogen on Earth…

It is a law of the universe that all things tend towards their most stable form. Hydrogen is most stable as a gas under normal conditions, hence why it normally exists as one. Metallic Hydrogen won’t be stable under normal conditions; it might just quickly convert itself back into a gas as soon as the high pressures are removed. However it might just be ‘metastable’. This would mean that the metal converts itself back into gas over a very long time period, allowing the metal to stick around long enough to be observed and to be used.

Making metallic Hydrogen metal under these conditions is all well and good, but unless the it can survive under normal conditions, it’s not very useful at all. This brings us to the second main criticism: if the metal only exists under conditions that took decades to find, it won’t be practical for the all the incredible applications that have been proposed for it.

The small sample is being specially stored to ensure it doesn’t break down. As such, the result of supposedly creating metallic hydrogen were published quickly, in case this precious substance was lost by further tests. The scientists now plan to test whether what they have made is indeed metastable: these coming experiments will probably be more important than the discovery of the substance itself.

 

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