Metallic hydrogen
If hydrogensufficiently compressed thenwill undergophase changeMetallic Hydrogen will result. Metallic hydrogenan exampledegenerate matter. It consists oflatticeatomic nuclei (namely protons) withspacing thatsignificantly smaller thanBohr radius, indeed more comparablean electron wavelength. The electronsunboundbehave likeconduction electrons inmetal.
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2 Cosmology 3 Applications |
Discovery
Though toppingperiodic table’s alkali metal column, hydrogennot, under ordinary conditions, an alkali metal itself. In 1935, however, Nobel Prize-winning physicist Eugene Wigner predicted that under immense pressure, hydrogen atoms would indeed join their first period kin, relinquishing their proprietary hold over their electrons.
The pressures required made experimental verification elusive. In March1996, however,groupscientists at Lawrence Livermore National Laboratory reported thathad serendipitously produced -aboutmicrosecond,at temperaturesthousandskelvinspressuresovermillion atmospheres -first identifiably metallic hydrogen, ending60-year search.
The Lawrence Livermore team did not expectproduce metallic hydrogen, aswere not using solid hydrogen, thoughtbe necessary,were working abovetemperatures specified by metallization theory; furthermore,previous studieswhich solid hydrogen was compressed inside diamond anvilspressuresup2.5 million atmospheres, detectable metallization did not occur. The team sought simplymeasureless extreme conductivity changes thatexpectedtake place.
The researchers used1960s-era light gas gun originally usedguided missile studiesshoot an impactor plate intosealed container containinghalf-millimeter-thick sampleliquid hydrogen. Put more comprehensibly,used an ultra-high-tech "Super-Soaker" water gun.
To shootstreamwater out ofSuper-Soaker, one first vigorously pumpshandlebuild up pressure inside, then pullstrigger, which releasesvalve -water shoots at tremendous speed onto your cowering friend. The light gas gun was merelyscaled-up version withfew variations:shot gas insteadwater, andshooting was not an enditself butmeanspropel"bullet" towardclosed containerhydrogen.
First, at one end ofgun,hydrogen was cooledabout 20 K insidecontainer that includedbattery connected by wires toRowgowski coilan oscilloscope;wires also touchedsurface ofhydrogenseveral places, soapparatus could be usedmeasurerecord its electrical conductivity. Atopposite end, upseven poundsgunpowder were lit, andresulting explosion pushedpiston throughpump tube, compressinggas inside. Eventually, like an overinflated innertube springingleak,gas reachedpressure high enoughthrowvalve atfar end ofchamber. Enteringthin "barrel",propelledplastic-covered metal impactor plate intocontainer at up18,000 miles per hour (a speed, byway, that would take you from DetroitNew York Cityaboutminute45 seconds), which compressedhydrogen insidemuchwayflycompressed when swatted.
The scientists were stunnedfind that as pressure rose1.4 million atmospheres,electronic energy band gap (a measureelectrical resistivity) fellalmost zero.
The electronic energy band gaphydrogenits uncompressed stateabout 15 eV, makingan insulator, but as pressure risesalmost unimaginable heights,band gap gradually falls0.3 eV. Because 0.3 eVprovided bythermal energy offluid (remember,pressure increased tremendouslyP1/T1=P2/T2, sotemperature became about 3000º K),hydrogen can at this point be considered fully metallic.
Cosmology
This has astronomical implications - astronomical, literally: metallic hydrogenpresenttremendous amounts ingravitationally compressed interiorsJupiter, Saturn,some ofnewly discovered extrasolar planets. Because previous predictions ofnaturethose interiors had takengranted metallization athigher pressure thanone at which we now know ithappen, those predictions must be adjusted. The new data indicate that much more metallic hydrogen exists inside Jupiter than thought, thatcomes closer tosurface,therefore that Jupiter’s tremendous magnetic field,strongestany planet insolar system, is,turn, produced closer tosurface.
Applications
Therealso uses forinformation thatcloserhome, though no less exotic. One methodproducing nuclear fusion involves pointing laser beams at pelletshydrogen isotopes;increased understanding ofbehaviorhydrogenextreme conditions could helpincrease energy yields.
But aside from gathering data,may be possibleactually produce fair quantitiesmetallic hydrogen,practical benefit. The existence has been theorized offormit (called 'Metastable Metallic Hydrogen', abbreviated MSMH) that would not revertordinary hydrogen upon releasepressure, just as diamonds freed fromcompression ofunderground do not revertordinary graphite. Withtensile strengthaluminum andthird its weight, MSMH could be usedbuild extremely light, fuel-efficient cars. In addition,would make an efficient fuel itself (andclean one,only hydrogen as an end product); 9 times as dense as standard hydrogen,would give off considerable energy when revertingthat form. "Burned" more quickly,could bepropellantfive timesefficiencyliquid H2/O2,current space shuttle fuel. Unfortunately,Lawrence Livermore experiments produced metallic hydrogen too brieflydetermine whether metastabilitypossible.
