Metallic Hydrogen

Synopsis:
Compress the hydrogen to some decent level. PERHAPS a diamond anvil pressure cell will not be needed (can only sqeeze a small quanitity with one of those!). When the hydrogen is compressed sufficiently, zap it with a laser, at a frequency specially tuned to momentarily ionize some of the hydrogen. At the main ultraviolet Lyman line, I think (but this may be a different value for pressurized hydrogen). The absorption of that ultraviolet, and the forced breaking of molecular bonds, offers the chance that when the bonds reform, metallic hydrogen will be produced, as being the lowest-energy-state available, in this highly pressurized scenario. The pressure should actually be relieved some, by the formation of the metallic hydrogen. So, increase the pressure again, and zap it again, and so on.

Background and Details:
Many of the chemical elements can exist in more than one pure form. A classic example is carbon, which manages to have an actual list of different forms: amorphous, graphite, diamond, buckminsterfullerenes, and nanotubes. I won't promise that this list is complete, or will never be extended, because carbon has proved to be so versatile! Anyway, each such differing form of a pure element is called an "allotrope". Oxygen and Ozone are allotropes of that element. Sulfur is normally found in a powdered-crystalline form, but can also exist in an allotrope that is actually somewhat rubbery in properties ("rubber sulfur" it is indeed called). Tin is normally metallic, but if the temperature is cold enough, it turns into a non-metallic powdery form (there is a tale about this happening to some statue in Russia one winter -- it disintegrated -- a century or two ago). Anyway, this Idea concerns ordinary elemental hydrogen, normally gaseous, which has been theorized to be able to exist in a metallic form. (Carbon, too, may have a metallic form -- what'd I tell you!?)

Theory indicated that very great pressure could force hydrogen to become a metallic allotrope, and the theory was somewhat verified in the laboratory about a decade ago. The electrical properties of hydrogen do indeed become indicative of a metallic state, under appropriate high-pressure conditions. However, those experiments destroyed the samples just as fast as they were created, so no long-term study was possible. A big question, then, concerns what happens when metallic hydrogen is created and the pressure is gently eased. Will the hydrogen revert back to a gas? Will it stay stable, and turn out to be a useful material? (I wonder about the effects of oxygen-corrosion, though!)

Anyway, before we can answer that question, we first must be able to make some metallic hydrogen that can be studied for a decent amount of time. If it explodes upon release of the pressure, then that is answer enough -- but then it may prove to be useful in bombs! So, this Idea is about making suitable quantities of metallic hydrogen, first for the purpose of study, and then, if the stuff is stable, especially at ordinary temperatures, for lots of other purposes later. For example, it has been suggested that metallic hydrogen could be a suitable material for building a classic Space Elevator, due to its extreme light-weight-ness. Even if only one-tenth as strong as carbon fibers, at the atomic level it weighs 1/12 as much, and therefore could have a superior strength-to-weight ratio...

The standard notion for squishing hydrogen into a metal is exactly and simply that: Just pile on the pressure until the intermolecular and/or interatomic chemical bonds give way, after which they should naturally reform into the kind of bonds typical of metals. This is a brute-force and inefficient approach (but it is known able to convert graphite into diamonds, when heat is added). This approach requires something with interatomic and/or intermolecular chemical bonds that are stronger than hydrogen, just for starters. This is where the "diamond anvil pressure cell" comes into the scene. A remarkably small gadget, the tips of two "brilliant cut" diamonds are sawed off, and the just-created flat faces of those diamonds are used as the squeezing zone. The tiny sample to be compressed is placed between the two diamonds, and then the thumbscrews are turned...(well, maybe not old-fashioned torture-chamber thumbscrews). One of the neat things about this type of pressure cell is that diamonds are transparent, allowing close examination (usually via laser beam) of the sample being squeezed. OK, it happened that while I was refreshing my memory about metallic hydrogen experiments, I came across a notation to the effect that one of the failure modes encountered by experimenters is that the hydrogen has a tendency to seep into the diamond! Obviously, there is a problem with this brute-force approach, to break hydrogen's bonds.

Well, there are other ways to break intermolecular and/or interatomic chemical bonds. The whole science of spectroscopy is based on measuring the energy (particularly in the form of photons) that is associated with the breaking and/or formation of such bonds (and intra-atomic bonds, too!). We KNOW exactly how much photonic energy is needed to break up hydrogen bonds, hydrogen molecules, and hydrogen atoms. More, there is a "resonance" phenomenon involved here, where atoms and molecules are naturally susceptable to absorbing those precise quantities of photonic energy -- and then breaking apart! (UV photons of main Lyman line, mentioned earlier, can directly ionize a plain/quiet hydrogen atom.) Finally, the development of lasers has reached the point where we can specify just about any frequency/energy of photon that we want to generate. If we can use lasers to separate isotopes of uranium (very similar spectra they have), then we can use lasers to break up intermolecular and/or interatomic hydrogen bonds, inside a pressure chamber -- and in significant quantities.

So, suppose we create a nice ordinary pressure chamber, something on the order of the things being used today to make synthetic gem-quality diamonds, and put a nice ordinary sort of extreme squeeze on some hydrogen. One possibility that I have wondered about, over the years, is the idea of putting pressure chambers inside other pressure chambers. Each one only has to withstand the difference between its inside and outside pressures. Anyway, we shine some specially tuned laser beams into the highly pressurized hydrogen, knowing that various bonds WILL break and reform. Will they reform as metallic hydrogen? Maybe, maybe not. But certainly it's worth finding out. This is where what I wrote in the Synopsis, about the "lowest energy state", becomes a factor. The existing theory is that if hydrogen's ordinary bonds are broken by squishing, then their only reformation option is the metallic state. However, that theory also indicates a temperature/pressure Zone for the existence of metallic hydrogen, and I am counting on it to allow the stuff to form with less squishing, provided that some other means exists to break hydrogen's ordinary bonds.

Finally, if we find ourselves needing the extreme pressures that only the diamond anvil cell can provide, in addition to lasers, well, that option will still be available (only tiny quantities of metallic hydrogen could be produced in that case, though, not enough for wide use, but at least enough for learning all about the stuff).