Producing metallic hydrogen was a complex condensed matter physics problem that scientists had been working on for decades. Such a material is capable of serving as an excellent superconductor at room temperature and exhibiting metastable properties when pressure is released, and could have a significant impact on medicine and rocket science.
Harvard researchers have managed to produce hydrogen with the properties of a metal. The results of a landmark scientific experiment by Ranga P. Dias and Isaac F. Silvera were published last week in the journal Science .
The material was created by compressing a container of molecular hydrogen between two artificial diamonds under ultra-high pressure and low temperature conditions. The press pressure reached 495 GPa, which is about 5 million atmospheres, while the temperature was reduced to minus 270 degrees Celsius.
As a result of this impact, a process occurred that is inherent in metals - hydrogen atoms lined up in a structure similar to a crystal lattice and began to exchange electrons. Researchers assumed the ability of hydrogen to transform into a metal state more than 80 years ago. The value of metallic hydrogen lies in its properties, which currently are not fully possessed by any of the known materials.
Metallic hydrogen is assumed to be metastable. In practice, this means that even if it is returned to normal environmental conditions, it will not change its properties. Scientists also say that metallic hydrogen can be a superconductor even at room temperature, which will allow achieving previously unprecedented results in the transmission and storage of energy.
It is reported that scientists are already interested in the discovery, since the use of metallic hydrogen as fuel will provide the opportunity to create powerful thrust and launch massive devices into space.
Scientists now need to determine for sure whether metallic hydrogen is truly metastable and learn how to create it in large quantities, since not the entire scientific community agrees with their interpretation of the experimental results.
Metallic hydrogen consists of highly compressed nuclei. In nature, the substance is found inside gas giants and stars. Hydrogen is in the first position of the alkali metal group in the Periodic Table. In this regard, scientists assumed that it may have pronounced metallic properties. However, this is theoretically only possible at extreme pressures. The atomic nuclei of metallic hydrogen are so close to each other that they are separated only by the dense electron liquid flowing between them. This is significantly less than the density of neutronium, a theoretically existing substance with infinite density. In metallic hydrogen, electrons merge with protons to form a new type of particle - neutrons. Like all metals, the material is capable of conducting electricity. It is when current is applied that the degree of metallization of such a substance is measured.
Receipt history
This material was first synthesized in laboratory conditions as recently as 1996. This happened at the Livermore National Laboratory. The lifetime of metallic hydrogen was very short - about one microsecond. It took a temperature of about a thousand degrees and a pressure of over a million atmospheres to achieve this effect. This came as a complete surprise to the experimenters themselves, since it was previously believed that very low temperatures were required to produce metallic hydrogen. In previous experiments, solid hydrogen was subjected to pressures of up to 2,500,000 atmospheres. At the same time, there was no noticeable metallization. The hot hydrogen compression experiment was carried out only to measure various properties of the material under these conditions, and not for the purpose of producing metallic hydrogen. However, it was a complete success.
Although the metallic hydrogen produced at the Lawrence Livermore National Laboratory was in a solid state, a theory has emerged that this substance can also be obtained in liquid form. Calculations have shown that such a material can be a superconductor at room temperature, although this property is not yet applicable for practical purposes, since the cost of creating a pressure of a million atmospheres is much higher than the amount of material obtained in monetary terms. However, there is a small possibility that metastable metallic hydrogen may exist in nature. According to experts, it retains its parameters even in the absence of pressure.
Metallic hydrogen is believed to exist in the cores of the large gas giants in our planet. These include Jupiter and Saturn, as well as the hydrogen shell near the Sun's core
METAL HYDROGEN- a set of high-pressure hydrogen phases with metallic properties. properties. Possibility of transition of hydrogen into metallic. phase was first theoretically considered by Yu. Wigner and H. B. Huntington in 1935 [I]-^B further, as methods of electronic theory of metals developed, the level of state of metallic. hydrogen phases were studied theoretically. In Fig. Figure 1 shows the phase diagram obtained by synthesizing the results of these calculations with experiment. and theoretical data on the level of state of molecular hydrogen. At atm. pressure and low temps, hydrogen exists in the form of dielectric. molecular crystal, with increasing pressure there is a transition to crystalline. metallic state. At the same time, depending on the temperature, 3 phases of M. v. are possible. At temperature T= 0 K and pressure r = 300-100 GPa metallization is accompanied by a restructuring of the crystalline. structures, H 2 and metallic. the crystal becomes atomic. At T> 10 K metallization is possible while maintaining the structure of the molecular crystal (dotted line; metallization of this type was previously observed in iodine). With a further increase in pressure or temperature, metallic occurs. phase and a liquid atomic M. c. is formed.
Metallic hydrogen
Metallic hydrogen- a set of phase states of hydrogen that is at high pressure and has undergone a phase transition. Metallic hydrogen is a degenerate state of matter and has some remarkable properties - high-temperature superconductivity and high specific heat of phase transition. The existence of a solid crystalline and liquid phase of metallic hydrogen, in which there is no long-range order, is possible.
History of research
In 1935, Y. Wigner and H. B. Huntington predicted the transition of hydrogen to the metallic state under high pressure (about 25 GPa) and the loss of a valence electron by the nucleus. Subsequently, estimates of the pressure required for phase transition have been increased, but the transition conditions are still considered potentially achievable. The properties of metallic hydrogen are predicted theoretically. Attempts to obtain it, begun in the 1970s, led to a series of experiments by M. Eremets in 2008 and Eremets and Troyan in 2011. However, there are doubts about obtaining metallic hydrogen.
Theoretical properties
Solid metallic hydrogen
The crystal lattice of solid metallic hydrogen is formed by hydrogen nuclei (protons) located from each other significantly closer than the Bohr radius, at a distance comparable to the de Broglie wavelength of electrons. Thus, electrons are weakly bound to protons and form a free electron gas, just as in metals.
Liquid metallic hydrogen
Liquid metallic hydrogen is formed by melting solid metallic hydrogen. Unlike helium-4, which is liquid at normal pressure and temperatures below 2.17 K, the existence of liquid metallic hydrogen under such conditions has been questioned. The energy of zero-point vibrations in an array of densely packed protons is high, and the transition from the crystalline phase is expected at high pressures. A study of the maximum melting point in the phase diagram of hydrogen by N. Ashcroft allows for a pressure region of about 400 GPa at which hydrogen is a liquid metal at low temperatures. Egor Babaev predicted that metallic hydrogen could represent a new state of aggregation: a metallic superfluid liquid.
Superconductivity
Metallic hydrogen has superconductivity at temperatures down to room temperature, which is much higher than other materials.
Experimental attempts to obtain
Shock compression: W. Nellis Supposedly produced metallic hydrogen in shock compression experiments 2008 and 2011 experiments. Shock compression. Preparation by pressure in diamond anvils.
Connections to other areas of physics
Metallic hydrogen can exist in the cores of giant planets.
Application
Fuel cells are proposed that use the energy released from the phase transition of metallic hydrogen into the dielectric state when the pressure is removed.
see also
Notes
Wikimedia Foundation. 2010.
See what “Metallic hydrogen” is in other dictionaries:
A set of high-pressure hydrogen phases with metallic properties. properties. Possibility of transition of hydrogen into metallic. phase was first theoretically considered by Yu. Wigner and H. B. Huntington in 1935 [I] ^B further as methods developed... ... Physical encyclopedia
A; m. Chemical element (H), a light, colorless and odorless gas that, when combined with oxygen, forms water. ◁ Hydrogen, oh, oh. In the given connections. In suspended bacteria. B bomb (a bomb of enormous destructive power, the explosive action of which is based on ... ... encyclopedic Dictionary
Solid state of aggregation of hydrogen with a melting point of −259.2 °C (14.16 K), density 0.08667 g/cm³ (at −262 °C). White snow-like mass, crystals of hexagonal system, space group P6/mmc, cell parameters a = 0.378... ... Wikipedia
Magnesium metallicum, Magnesium metallicum- Chemical element of the 2nd group of the periodic system of Mendeleev. It is found in nature in the form of magnesite, dolomite, carnallite, bischofite, olivine, and kainite. Silvery metal does not oxidize at ordinary temperatures in dry air, with cold water... ... Handbook of Homeopathy
Recently, two scientists, Mikhail Eremts and Ivan Troyan, as a result of laboratory experiments, managed to do something that many physicists and chemists could not achieve - to obtain metallic hydrogen. As is known, this element in a similar state can exhibit the properties of a superconductor at room temperature. Therefore, the discovery became a real sensation.
I think many of us, even when we were in school, often wondered why hydrogen, known to everyone and dearly loved by us, is in two groups in the periodic table - in I and VII. And, probably, those who asked this question to a chemistry teacher learned from him that this happens because since the 1s electronic level contains no more than two electrons, then the hydrogen atom (which has one) in general does not care - for In order to achieve a stable electron configuration, you can both gain someone else's electron and lose your own electron.
That is why it can give up an electron, as metals do (in the formation of hydrogen halides), and also attract someone else’s to itself, as non-metals do (in the formation of metal hydrides). Moreover, as experience shows, hydrogen is given more readily than taken away. Based on this, it is logical to assume that “at heart” it is still metal.
However, not everything is so simple, especially when it comes to the physical properties of this element. Normally, as we remember, hydrogen is a gas, but this is not typical for metals; under normal conditions, they are most often solids (and only sometimes liquids). In addition, hydrogen in its pure form behaves as a dielectric, while metals are normally conductors. Based on this, most chemists and physicists tend to perceive this gas as a non-metal.
However, some scientists believe that under special conditions hydrogen can be made to behave as a metal should. Back in 1935, American researchers Eugene Wigner and Hillard Huntington suggested that molecular hydrogen under high pressure conditions (something in the region of 250,000 atmospheres) should acquire metallic properties. Moreover, according to calculations, metallic hydrogen can transform into a superconducting state at a temperature of 200-400 K (and this is from -73 to + 127 degrees Celsius, that is, room temperature also falls into this range!).
Scientists also found that metallic hydrogen may turn out to be metastable, that is, after removing the pressure, it will not immediately return to the usual state of a gas with dielectric properties, but will remain a superconductor for some time.
As you can see, if people managed to somehow obtain metallic hydrogen, then the problem of creating electrical superconductors that operate at temperatures normal for humanity would be solved once and for all. But the problem is that there is practically no such thing in nature. True, it is believed that it can be in sufficient quantities in the upper layers of the “crust” of Jupiter, where, as is known, the pressure is very high, but you cannot get it from there. There’s no way we’re going to fly to neighboring Mars, let alone Jupiter...
That is why scientists have been trying to obtain metallic hydrogen in the laboratory for quite a long time. However, the question of whether the desired “metallization” was observed in these experiments remains controversial - the researchers could not provide convincing evidence. Moreover, a number of experiments even indicated the opposite - in recent experiments conducted at temperatures below 100 K, it was shown that hydrogen retains a molecular dielectric state even under a pressure of 300 GPa. That is, even in such hellish conditions, the stubborn element did not want to become metal.
However, the other day the entire scientific world was shocked by the news that two scientists from the Max Planck Institute of Chemistry in Mainz, Mikhail Eremets and Ivan Troyan, were able to obtain the long-awaited metallic hydrogen in laboratory conditions. As follows from the article by the experimenters (you can read it), they used the so-called diamond anvil - an installation of two diamond crystals, between the tips of which an insulating gasket was placed.
A sample (gas in a compressible container) with a diameter of ~10 and a thickness of ~2 μm was placed in its hole. To record the resistance, thin (about 50 nm in diameter) electrodes were connected to it. After which the scientists gradually increased the pressure and monitored changes in the properties of hydrogen. By the way, all this happened at room temperature (that is, at 295 K or 22 degrees Celsius).
According to the experimenters, when the pressure reached 178 GPa, the hydrogen and the insulating gasket remained transparent. However, later, at 200 GPa, the sample began to darken, that is, it became opaque (the first evidence of its transformation into a metal). With a further increase in pressure, at around 234 GPa the sample became completely opaque, and at 250 GPa, and even more, it began to reflect light (that is, it began to shine, like most metals).
It was also found that a pressure of 220 GPa led to the appearance of electrical conductivity in the sample, and an increase in pressure to 260-270 GPa caused a sharp increase in conductivity, which stabilized at a new level and practically did not change if the pressure was raised to 300 GPa. Physicists consider such a change in the characteristics of a substance to be a sign of a transition to the metallic state.
Interestingly, a similar assumption was confirmed during control laser irradiation: at pressures up to 260 GPa, the impact of a helium-neon laser on the sample led to a decrease in resistance, and after that it gave the opposite effect (which usually happens under such conditions with metals).
To finally make sure that they managed to obtain metallic hydrogen and not something else, Eremets and Troyan cooled the sample to 30 degrees Kelvin. And although the resistance increased slightly, the sample did not lose electrical conductivity. remained conductive. The reverse transformation of the metal phase into molecular hydrogen began only when the pressure was reduced to 200 GPa.
So, apparently, German physicists of Russian origin, Mikhail Eremets and Ivan Troyan, managed to obtain metallic hydrogen for the first time. And although this discovery made a huge impression on many colleagues, there were also skeptics who doubted the correctness of the experiment. They note that in these experiments, metal electrodes and epoxy resin could interact with hydrogen during compression and greatly distort the results.
And authoritative materials scientist Arthur Ruoff from Cornell University (USA) points out one oddity - in his opinion, it seems very suspicious that the resistance of the metal sample when cooled to 30 K increased by as much as 20 percent! He notes that for a typical metal under such conditions it should either decrease or show a much more significant increase.