Experimental Attempt to Metallize Hydrogen at Very High Pressures

Metallic hydrogen is potential candidate as a high energy density material. The possibility of metallizing hydrogen by submitting it to very high pressures has been experimentally investigated. Great advances have been made in this study. Pressures as high as 2.3 megabar on hydrogen have been obtained in diamond anvil cells (DACs). Several new phase transitions have been observed in the megabar pressure region. One of these, called the hydrogen-A (H-A) phase is believed to be the metallic molecular phase of hydrogen. However, current limitations on the optical techniques available to diamond anvil cell research have prevented direct determination of the conductive state and techniques for the direct measurement of the dc electrical conductivity are still under development. Band structure calculations have shown that metallization may be profoundly affected by molecular orientational order. Other observed phase transitions are believed to be associated with orientational order and fundamental changes in the molecular symmetry at high densities. A pulsed NMR system for studying very small samples of hydrogen has been constructed and will be useful in analyzing the nature of high density hydrogen. Metallic hydrogen, high pressure.