Metallic Hydrogen: The New Superconductor

Avery Parr, Staff Writer

Hydrogen is the most abundant element in the universe. It makes up 75% of it, in fact. It is a key ingredient in the water that covers 71% of the Earth. In a few years, it might power our cars and our homes. However, scientists have been looking into even more complex applications of this natural resource, and it seems that they have found one.

On January 26, 2017, Harvard postdoc Ranga Dias and Professor Isaac Silvera found a way to create metallic hydrogen, something that scientists have been trying to do for close to a century.

Anyone familiar with the periodic table will tell you that hydrogen is usually found directly above the alkali metals (lithium, sodium, potassium, etc.) yet looks nothing like the others. Hydrogen takes a gaseous form at room temperature and doesn’t become a liquid until you cool it down to -252.9 ˚C.

However, around 100 years ago, it was theorized that, under great pressure and exceedingly low temperature, hydrogen would become a metal like its alkali metal brethren, and it would have some particularly interesting properties.

Unfortunately, it turned out not to be particularly easy to create a metal out of a gas. Calculations showed that it would take at least 300 GPa (approximately 3 million times normal atmospheric pressure) to even have a chance of creating such a material. Of course, this did not stop scientists from trying.

On January 26, 2017, they finally succeeded. The process that Harvard postdoc Ranga Dias and Professor Isaac Silvera used was as follows:

  • Take small synthetic diamonds, and remove all micro-imperfections on the surface through a special process.
  • Coat the diamonds in alumina to prevent hydrogen from getting into the crystal and changing the crystal lattice.
  • Squeeze these diamonds together in a chamber filled with hydrogen gas using screw gears to ensure a huge amount of pressure.

If this process is followed until the pressure reaches roughly 335 GPa (50 million psi), the hydrogen changes into a phase called “black hydrogen.” This in and of itself is a slightly miraculous substance – it is entirely opaque. However, black hydrogen was not the golden prize the scientists were searching for.

That prize is found at approximately 50% more pressure. At the ridiculous pressure of 495 GPa (71.7 million psi, or 5 million times atmospheric pressure), the molecular structure of hydrogen breaks down, and you are left with a pure metal, one with rather remarkable properties in wiring and in rocketry.

Before we continue, it is important to discuss two definitions: “superconductor” and “metastable.” A superconductor is a material that when cooled below a certain temperature allows for conduction of electricity without loss of energy. Something that is metastable is at least temporarily stable under normal conditions but eventually returns to a more stable state over time.

One of metallic hydrogen’s most exciting properties is that it acts as a superconductor at room temperature. In comparison, the highest-temperature superconductor we are currently able to create (extremely compressed hydrogen sulfide) only functions at temperatures below -70 ˚C.

As the Harvard press release puts it, “As much as 15 percent of energy is lost to dissipation during transmission.” This new advancement could lower energy costs significantly.

Metallic hydrogen’s most powerful application, however, is its capability to store the massive amounts of energy it takes to produce it. Once stored, this energy can be spent violently and rapidly to provide propulsion.

As it turns out, metallic hydrogen is approximately four times as powerful as the strongest propellant we have currently (which is also hydrogen, as a matter of fact – liquid hydrogen).

However, there have been criticisms of this recent publication as it stands. First and foremost is the lack of replication. This study has not been repeated, and therefore the reported metal could well have been an experimental fluke.

The first indication that the research team used to determine that the product was in fact a metal was that it gained a luster uncharacteristic of its natural state. Others have since pointed out that this could have been the alumina covering on the diamonds, instead of hydrogen.

Even though there are criticisms, however, this discovery represents a large step forward in condensed matter physics. If it is later proven false, then we know what we need to do differently in the future. If it is shown to be correct, however, then we have just created the rarest material on Earth.