> We used type IIac conic synthetic diamonds (supplied by Almax Easy-Lab) with ~30 micron diameter culet flats. About 5 microns were etched off of the diamond culets using the technique of reactive ion etching, to remove defects from the surface. The diamonds were then vacuum annealed at high temperature to remove residual stress. Alumina is known to act as a diffusion barrier against hydrogen. The diamonds, with the mounted rhenium gasket, were coated with a 50 nm thick layer of amorphous alumina by the process of atomic layer deposition.

Incredible technology!

> The pressure was initially determined to ~88 GPa by ruby fluorescence using the scale of Chijioke et al (20); the exciting laser power was limited to a few mW. At higher pressures we measured the IR vibron absorption peaks of hydrogen with a Fourier transform infrared spectrometer with a thermal IR source, using the known pressure dependence of the IR vibron peaks for pressure determination (see SM).

Just incredible!

> Photos were taken with a smartphone camera at the ocular of a modified stereo microscope

...

> Photos were taken with a smartphone camera at the ocular of a modified stereo microscope

Still incredible! We as people tend to underestimate just how "magical" our mobile phones are.

Considering the expensive equipment and processes, it's a wonder why they didn't use any scientific-grade CCD sensor.

Rare that I lough out loud at Hacker News.

Drives home the "more computing power than the Apollo program" bit of trivia, doesn't it?

Super cool stuff! There are some greatly quotable sentences in the paper:

> Moreover, SMH (solid metal hydrogen) is predicted to be metastable so that it may exist at room temperature when the pressure is released. If so, and superconducting, it could have an important impact on mankind’s energy problems and would revolutionize rocketry as a powerful rocket propellant.

> The principal limitation for achieving the required pressures to observe SMH in a DAC (diamond anvil cell) has been failure of the diamonds.

> The sample was cryogenically loaded at 15 K and included a grain of ruby for pressure determination.

> As of the writing of this article we are maintaining the first sample of the first element in the form of solid metallic hydrogen at liquid nitrogen temperature in a cryostat.

If it's stable at room temperature wouldn't it make a really high density fuel too?

Metallic Hydrogen can also be a liquid and even a gas, the metallic part indicates it's an electric conductor, not a solid. The "idea" behind metallic hydrogen is that since hydrogen is above the alkali metals in the periodic tables there should be a phase where it behaves like a metal, the state of the phase is not defined as a solid/gas/liquid in fact in all honesty it would exist as all 3 and more.

The first production of metallic oxygen was a liquid, this is the first solid one, tho at these pressures it's really unlikely that it would effective as fuel store. One of the more interesting parts about metallic hydrogen is the information we learn also applies to hydrides (hydrogen alloys) especially things like Lithium-Hydrogen since basically you can stabilize a large amount of hydrogen atoms (6 or more) around a single atom of Lithium, this might actually be very interesting for a lot of applications including energy storage. Hydrides should be considerably more stable and more importantly at considerably lower pressures which would mean that they can actually be used for various applications since you are not going to find something that only can exist at 400 gPA levels of pressure or higher very useful for high stress applications.

Metallic hydrogen is atomic, recombining two atoms into an h2 molecule releases huge amount of energy. Iirc 4x as much as burning h2 in oxygen.

This is the principle behind atomic hydrogen welding. An electric arc converts the hydrogen to atomic form, which recombines to molecules when it hits the surface. The hydrogen is also strongly reducing so you don't need flux. It still has some niche uses but it's not used much now because of risk of hydrogen embrittlement.

There's an interesting instructional video about this on Youtube: https://www.youtube.com/watch?v=uZwYMyHlWXk

Technically it's degenerate matter since the atoms do not interact due to the pressure and other conditions, this happens because the electrons would have to follow the exclusion principle under those pressures/densities the electrons basically separate from the hydrogen proton as they cannot occupy the same space and the hydrogen becomes a degenerate matter; a sea of electrons flowing freely through a lattice of protons, because of this none of the "atoms" can combine into molecules, but they aren't technically atoms at that point either.

The problem with hydrogen as fuel storage (mainly for space travel) is the pressure, operating a fuel tank at 400 gPA or higher is going to be tricky, I've edited my previous post and added the bit about Hydrides which might actually considerably more viable for both terrestrial and space applications.

If we can actually make LiH6 alloys and can find an easy way to break them apart it can be a great fuel source, yes we might have to carry some "dead weight" but Li has an atomic number of 3 Oxygen has an atomic number of 8, considering that Hydrogen-Oxygen reaction is pretty much 1 to 1 (well "2") we have to carry considerably more Oxygen now than we would have to carry Lithium. If a Hydrogen-Hydrogen reaction could be harvested as a propellant it would still be more effective than what we have even if we don't find any clever ways of catalyzing the lithium we already carry to push the reaction even further, we might be able to carry a smaller amount of oxygen also to catalyze the lithium tho I'm not sure if the energy from that reaction would be worth the added weight of the oxygen and the parts of the fuel and propulsion systems that would support it and the O-Li process.

P.S.

Metallic hydrogen is also of "interest" to those who still study cold fusion, even tho you can't call it cold fusion any more due to the stigma, at certain conditions there is a high likelihood of Inertial Confinement Fusion and Pycno Nuclear Fusion occurring, this often brought up as "superconductor fusion" simply because you can't call anything cold fusion and get it published.

That might also be a quite interesting fuel source, especially if you simply need to push it to a certain limit and once the fusion kicks in it would transition to other fusion stages.

And lastly this might be especially interesting if we can make Li-Deuterium alloys since D-Li fusion produces Helium 4 and over 20 MeV of energy :)

This (last) type of fusion is extremely interesting because not only it's highly energetic but it's aneutronic, which means that less than 1% of the energy is released via neutrons vs 80-90% in other forums of fusion, aneutronic fusion produces tons of energy an pretty much no ionizing radiation which means if you can make it work it would be in theory a safe enough battery to power a cellphone without frying your brain.

>The problem with hydrogen as fuel storage (mainly for space travel) is the pressure, operating a fuel tank at 400 gPA or higher is going to be tricky

Operating a fuel tank at 1 MPa is tricky. Operating a fuel tank at 400 GPa is ludicrous.

So that's how Spaceball 1 could reach ludicrous speed. You learn something new every day...

But your parent and grandparent comments are talking about the fact that the authors theorize it may remain metallic once the pressure is released.

I think in this context they just mean remain conductive, not solid or stable.

Metallic doesn't mean solid, metallic just means it will conduct electricity it will not be solid, or liquid at room temperatures and pressures.

From the paper:

"Moreover, SMH is predicted to be metastable so that it may exist at room temperature when the pressure is released (10). If so, and superconducting, it could have an important impact on mankind’s energy problems and would revolutionize rocketry as a powerful rocket propellant (11)."

I'm no chemist, but I'd expect it to be more of an explosive than a fuel.

Whether or not MH is metastable in the real universe, it -- or at least some form of it -- is metastable in Alastair Reynolds "Revalation Space" universe, and there ohh boy is it explosive.

To-may-to, to-mah-to....

I wonder what the specific impulse of the stuff would be.

The exhaust velocity would be 17 km/s according to:

http://www.projectrho.com/public_html/rocket/enginelist.php#...

> Super cool stuff!

Literally!

hell with rocket fuel, if the stuff isn't horribly expensive to produce it could be a good portable source period

This makes me wonder, what is the energy density of this stuff? And how easily does it release its energy? (Is it hazardous?)

TL;DR: Theres lots of energy (but less than I thought), it's probably (too) easy to release, so yep it's dangerous.

If I understand it correctly most of the energy (apart form E=mc^2 energy that can't be tapped easily) is what comes from the mechanical work squishing the hydrogen down to size.

That means the energy density should be in the order of the pressure, which is 495 GPa. So a cubic metre of the stuff would have half a terajoule of energy. Wikipedia says the Nagasaki bomb was about 90 terajoules.

If the stuff behaves in a simple way, you can release the energy by just releasing the pressure. If it is "metastable" that means it can somehow remain compressed when the pressure is released -- but will be "trying" to explode to its uncompressed state. We don't know if the metastable state even exists, let alone how easy it is to get out of.

Very exciting! For context, here's a nice long article (Aug 2016, 2 months before this arxiv paper came out) on the recent history of attempts to make it, with quotes from author of current paper and others in the field:

https://www.sciencenews.org/article/pressure-make-metallic-h...

> A few months later, Silvera’s group squeezed hydrogen hard enough to make it nearly opaque, though not reflective — not quite a metal. “We think we’re just below the pressure that you need to make metallic hydrogen,” Silvera says. His findings are consistent with Eremets’ new phase, but Silvera disputes Eremets’ speculations of metallicity. “Every time they see something change they call it metallic,” Silvera says. “But they don’t really have evidence of metallic hydrogen.”

> All this back and forth may seem chaotic, but it’s also a sign of a swiftly progressing field, the researchers say. “I think it’s very healthy competition,” Gregoryanz says. “When you realize that somebody is getting ahead of you, you work hard.”

I saw it! A tiny, shiny speck under the microscope, and the thrill of seeing a form of matter which, it can be argued, has never existed anywhere in the universe. Ever.

I'm being pedantic, but should be "human knowledge", not "universe". It is absurdly unlikely that the conditions needed for this substance to exist never occurred in the ~1,000,000,000,000,000,000,000 star systems in the known universe. "conditions needed" includes intelligent life creating these substances.

Would the pressures in a Jovian not be enough to form metallic hydrogen?

To get solid metallic hydrogen, you'd need both high pressure and low temperatures; in the celestial bodies that can provide the former, the latter seems unlikely.

Jupiter is indeed believed to have a liquid metallic hydrogen core, which is the source of its enormous magnetic field:

https://science.nasa.gov/science-news/science-at-nasa/2011/0...

By Jove?!

Your attempt at humour has been rightly sanctioned, but you weren't all that far from the mark. Jove is another name for the roman god Jupiter, and as such a Jovian planet is one that resembles Jupiter - ie. large gas giants, where metallic hydrogen is certainly thought to exist in nature.

Not by Jove - inside Jove.

That not only assumes it could never happen naturally, but also that we are the only intelligent life in the universe.

The aliens working undercover among us now are rolling their 7 photoreceptors at our anthropocentrism.

Are you assuming there's no other intelligent life in the universe? :-)

Just for reference the pressure at the center of the Earth is estimated to be around 360 GPa, while they are using 495 GPa and DACs able to reach over 700 GPa.

https://en.wikipedia.org/wiki/Diamond_anvil_cell

Jupiter, however is up to the task :)

Liquid Metallic hydrogen in Jupiter's core: https://science.nasa.gov/science-news/science-at-nasa/2011/0...

An absolutely silly pressure! For those who might not be familiar, standard steels fail at about 0.5 GPa

Guys, this is literally the holy grail of high pressure physics!

One of my co-workers got his PhD with the lab/advisor that published his paper. He thought they weren't going to be able to synthesize it, so he left to be a quant.

I sent him an email saying 'hey, isn't this what your PhD was on?'. Then, I looked up his thesis and saw that this was his thesis and, but this publication was from his lab, with his advisor as co-author.

Oh man. I hope I didn't cause any existential dread. He didn't just make a decision that cost him a Nobel, right?

What'd he say?

What, like they made a cup out of it already?

"Now that is the cup of a high-pressure physicist."

Wow, drinking from it causes eternal youth?

Yes. Well, except for the holes.

Exciting stuff!! Everything from practical uses to insight into Jupiter's core could come from this.

Someone with a chem/physics background, could you please explain why metallic hydrogen is only theorized to be a superconductor? Is such a property not predictable?

The problem (not having a condensed matter background, so my answer might not be entirely right) is that we can't solve the Schrödinger equation exactly for many-atom systems.

So we need to approximate our solutions to be able to get a good idea of what properties a material will have. Our approximations are pretty good and we have a decent idea of when some things superconductor. But our theories of superconduction aren't yet perfect, and sometimes the approximations can fail//generate behavior unexpected by our theories.

In general, we can only predict ground state properties with accuracy. Properly predicting high temperature superconductivity requires generating information about the Fermi surface that is not just a matter of ground states. If this is standard BCS model stuff then you might be able to get away with some rules of thumb.

495GPa... doesn't seem so bad...

Standard atmospheric pressure ~= 100Pa

So they increased the pressure in that chamber by 4.95billion times.

And then they hypothesise that the hydrogen metal could be stable at room temperature.

Oh. My. Days.

Standard atmospheric pressure is ~= 100kPa

Did they test if it's super conducting?

They comment about this at the end of the paper: "As of the writing of this article we are maintaining the first sample of the first element in the form of solid metallic hydrogen at liquid nitrogen temperature in a cryostat. This valuable sample may survive warming to room temperature and the DAC could be extracted from the cryostat for greatly enhanced observation and further study. Another possibility is to cool to liquid helium temperatures and slowly release the load to see if SMH is metastable. An important future measurement is to study this metal for high temperature superconductivity."

Out of curiosity, what made you ask this? Is there something about Hydrogen that would elicit such a question, or is that just a question that should be asked of any new material?

As I said, I'm genuinely curious. I'm not even an amateur here, but I wouldn't have thought to ask this at all.

Metallic hydrogen was theorized to be a superconductor in a 1968 paper: http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.21....

A high temperature superconductor at 500GPa is probably even less practical than a cryogenic superconductor.

So for this to be exciting we first need the even more exciting news that MH is metastable so that we can release the pressure. Then we can find out if we have a high temperature, high explosive, superconductor.

Even that is probably not of practical use. But by gum! It'd be fun.

The article states that solid metallic hydrogen is hypothesized to be stable at room temperature and superconducting.

It's predicted to be a high temperature semiconductor.