Graphic Illustration by Bryan Donoghue

The pressure’s on to make metallic hydrogen


By Bryan Donoghue

Within Humboldt State University, in the halls of Science A, there’s a cabinet that houses solid and metallic specimens of almost every element in the periodic table. One of the only absent solids is hydrogen, an element known for being gaseous. Hydrogen contains many impressive properties, one of which is its ability to form strong bonds, known as hydrogen bonds, with other elements. Just recently, two Harvard physicists named Isaac F. Silvera and Ranga Dias have created the correct conditions to form metallic hydrogen. This form of hydrogen is both a superconductor and metastable. If replicated, the results could be revolutionary.

The process to create this metallic form of hydrogen is delicate, but requires an immense amount of pressure on a single point. According to Harvard’s website, a level of 495 gigapascal of pressure was needed before metallic hydrogen started to form. A gigapascal is a measurement of pressure.

Robert W. Zoellner is a Humboldt State University chemistry professor who specializes in inorganic and organometallic chemistry. He has experience in using the device that gives off such pressure.

According to Zoellner, the device is known as a Diamond Anvil Cell. The Diamond Anvil Cell is a contraption in which two diamonds face parallel from one another and push against each other at a single point.

“The device is really easy to work with. Essentially it’s just a clamp that holds them,” Zoellner said. “It’s a very, very well built clamp, of course. With this clamp, you can literally turn a screw and increase the pressure on the diamonds.”

The use of diamonds is not only due to structural resilience, but also their transparency. To test the state of matter that hydrogen is in within the Diamond Anvil Cell, scientists use a method called Raman spectroscopy. Raman spectroscopy is a non-destructive way of characterizing diamond-like substances.

According to Zoellner, Raman spectroscopy is when laser light shone onto a molecule scatters and creates a different frequency of light than before. The frequency of the light corresponds to the vibration of the molecule, so detecting a change in frequency is all that’s needed.

Diamonds are an expensive commodity, especially the type IIA diamonds that Zoellner says are needed for this experiment. Due to the pressure being forced between them in the vise, these gems have an ability to break.

“The diamond is also vibrating,” Zoellner said. “The high intensity laser light goes through the diamond, it can excite those vibrations as well. If it does it too much, parts of the diamond will get hot, expand, and they crack and break.”

Zoellner says they use artificial diamonds which are cheaper than real diamonds, but still expensive.

“And they have to be polished and carefully machined and everything to make them fit properly. So, the higher the pressure, the more likely it is the diamonds will fail,” said Zoellner.

According to Silvera, the phase change happens at 495 gigapascal. This immense amount of pressure makes the hydrogen become reflective, indicating its transition into a metallic substance.

“The reason a metal is reflective is because of the electrons that are in it. Those electrons form a reflective sea of electrons, essentially, that cause the light to be reflected,” Zoellner said. “That’s why all the metals are silver, because they are highly reflective.”

The uses for metallic hydrogen may be vast with the possibility that it could eventually be metastable, meaning that it will stay in a metallic form for an extended period of time.

“Here, think of it this way,” Zoellner said, “If you take an ice cube out of your freezer and put it on your counter, does it melt completely, instantaneously? Takes a bit of time, right?”

Zoellner said that this is what the metallic hydrogen may be doing if it is metastable, only it will take a much longer period of time to change to a liquid or gas than an ice cube does.

According to Silvera, this gives metallic hydrogen the possibility of being used in magnetic resonance imaging scans (MRI scans) as magnets that can work at room temperature. Currently, magnets in MRI scans need to be cooled with liquid helium. Silvera also said that if metallic hydrogen is metastable and it can be converted to molecular hydrogen, it can release an enormous amount of energy. Seeing the potential use for this as rocket fuel, NASA supports Silvera’s research.

“Whenever you form a bond, you release lots of energy,” Zoellner said. “If you take a metallic hydrogen with twelve relatively weak bonds, those bonds require energy to break. So you put in some energy, but this is kind of like compound interest.”

According to Zoellner, we could call this proof of concept and that now people will begin thinking how to we make the process easier, faster and cheaper so that we can use it.

According to a report given by Silvera to NASA, “To transform solid molecular hydrogen to metallic hydrogen requires extreme high pressures, but has not yet been accomplished in the laboratory. In the proposed new approach electrons will be injected into solid hydrogen with the objective of lowering the critical pressure for transformation. If successful the metastability properties of hydrogen will be studied. This new approach may scale down the pressures needed to produce this potentially revolutionary rocket propellant.”

Once metallic hydrogen is one the market, Silvera and Zoellner predict that it will have great use as a superconductor, which means that it conducts electricity without losing any.

According to Silvera, you could create power lines that conduct electricity across the country without dissipating.

Zoellner said that Hoover Dam typically conducts its electricity to Las Vegas and possibly San Francisco and Los Angeles.

“Every foot, every mile that the electricity moves, some of it gets lost,” Zoellner said. “If all those lines were superconductors, you could transport it around the world without loss.”

In an article submitted to the Harvard community, Silvera said that metallic hydrogen is the most powerful rocket fuel to yet exist. Silvera has now taken steps to replicate the process. Soon, metallic hydrogen will have a place in the cabinet housed in Science A and continue to take the pressure off of our daily lives.

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