Tuesday, January 31, 2017

Two Harvard men claim to have produced metallic hydrogen

My former colleague (and the superhero who believes that love has no borders, nationality, or gender: don't worry, at the end of the film, your humble correspondent punishes the nasty illegal immigrant dragon for its murder of Ike and others) Isaac Silvera and his younger collaborator Ranga Dias claim to have achieved the holy grail of high-pressure physics: to turn hydrogen into a metal. The cores of Jupiter and Saturn may be full of solid hydrogen and solid helium.

The achievement was reported in Science:
Observation of the Wigner-Huntington transition to metallic hydrogen

Full text: arXiv.org (October 2016)
See also popular articles at The Cake, Sci News, and Google News.

If they're right, you may repeat the experiment in your kitchen. Take a breath of hydrogen, place it in your fridge, cool it to 3 kelvins, and then slam it with the hammer at the pressure of of 495 gigapascals. The hydrogen will become reflective – with albedo as much as 0.91. Before that point, you should see the hydrogen turning black at 335 gigapascals – the pressure just slightly below that of the center of the Earth. You may find small capsules made of artificial diamond helpful.

As The Wire and many others mention, most people in Silvera's field are highly skeptical.

In principle, I feel "almost certain" that hydrogen should be able to become metallic. Already in 1935, when people like Einstein and Schrödinger were still struggling with trivial things such as the very notion of entanglement in quantum mechanics, Eugene Wigner and Hillard Bell Huntington already applied quantum mechanics to calculate properties of a material (a macroscopic object, still governed by quantum mechanics like everything else!) not yet known, metallic hydrogen:
On the Possibility of a Metallic Modification of Hydrogen
Their estimate of the required pressure was modest 25 gigapascals (250,000 atmospheres). Later, this guess was raised by a factor of 20-25, to pressures that Silvera and Dias probed (around 5 million atmospheres).

Not every element or compound may be turned into a metal but have a look at the Mendeleev periodic table of elements. You know, hydrogen is in the first column that otherwise contains alkali metals (don't overlook the word "metals"), namely lithium, sodium, potassium, rubidium, caesium, and francium.

The classic Czech proverb designed to memorize the column is: Helenku bal Na Kolínku Robustní Cestář Frantík, i.e. Helene was being kissed on her knee by the robust road-mender Francis.

OK, hydrogen could be a metal just like every other metal. A material containing a crystal lattice with a continuous sea of shared electron states, high reflectivity, and an immensely good electric conductivity. But has it been achieved?

Silvera and Dias placed some hydrogen on a rhenium gasket and were increasing the pressure using an artificial diamond tip. Well, a "diamond anvil cell" (DAC) capable of withstanding the huge pressures was used. And suddenly it got shiny.

A JPG picture claimed to prove their success.

Other high-pressure physicists, especially those who tried to turn hydrogen into metal themselves but failed ;-), seem skeptical or grumpy. Their main alternative explanation is simple. Silvera and Dias claimed to have seen something shiny inside. But it could have been something else than hydrogen – namely the aluminum oxide that Silvera and Dias used as coating in a screw.

All the other materials (except for hydrogen?) that they have used are less shiny than the hydrogen was at the end, so they were eliminated. But the aluminum oxide in the coating could have turned into this very shiny metal as well – before the hydrogen did. And because of the deterioration of the coating, maybe the pressure that they describe – 495 gigapascals – wasn't ever achieved.

To summarize, it could have been a shiny aluminum oxide, and not hydrogen, that was observed by the happy Ike and his younger colleague.

My feelings are absolutely mixed. I don't know whether the critics are right. On one hand, I do think that that Ike is a very skillful guy and it should be possible to make it metallic because it's not quite qualitatively different. On the other hand, many other things may turn into really good metals – including the oxide – and they're rather likely to do so before the hydrogen (at lower pressures) because the hydrogen should be the last one, if it deserves the label of the holy grail, at least. ;-)

Also, when I was being forced to write a grant application, I was told by a grant-focused secretary that Ike Silvera was the ultimate hero who knows how to write the shiniest possible grant applications that wow the potential sponsors. This is perhaps another experience that slightly increases my suspicion that the reality of the hydrogen was less shiny that what it looked like.

Silvera and Dias have used numerous gadgets that they consider their friends, things to create huge pressure, microscopes etc. But the coating will have to be replaced by something else that could eliminate the doubts before most of their colleagues will believe it. Many critics say that the paper doesn't contain too many details.

If Dias and Silvera are right, after all there could be some cool futuristic applications. I've mentioned that the metallic hydrogen should be an excellent conductor. Well, it should really be a superconductor. And the superconductivity could potentially extend to high temperatures – well, you would probably still need the insanely huge pressures so I doubt it would become practical. Also, such hydrogen would be a good form of fuel. Rockets use liquid hydrogen.

Just for your convenience: hydrogen becomes liquid at 20 kelvins and (non-metallic) solid at 14 kelvins. The old-fashioned solid hydrogen was already created in 1899 and with its density 0.086 times that of water, it's by far the lightest solid we know.

I wish Ike and his pal a lot of good luck.

P.S. I: The video mentioned in the first sentence of the blog post is from the Jefferson Lab. It just happened, as I learned from Willie Soon, that a false bomb threat in Jefferson was reported yesterday. Most people inside didn't give a damn – they got used to the falsehood of such alarm. Well, at one moment, the alarm may turn out to be real. But it's possible that even in that case, panic won't help anyone too much.

P.S. II: I used the word "men" in the title. I hope that it's still OK in the U.S. Meanwhile, in the U.K., they are probably leaving the EU because they didn't find it insane enough. A new British government regulation bans physicians from using the term "mother". Instead, they must talk about pregnant persons or pregnant people, to be sure that the transgender persons aren't insulted and stripped of their hope that they will get pregnant, too. Good job, Brits. Your mothers must be proud about you. I meant your pregnant persons and copulating persons (or whatever is the PC word for fathers) must be proud about you. ;-)

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