Friday, April 21, 2017 at 11:00am to 12:00pm
Speaker: Dr. Raina J. Olsen, US Army.
Abstract: Interest in phases of hydrogen has persisted for over eight decades. Technological interest stems from the broad range of applications; hydrogen is already used as a clean and efficient fuel, and has been proposed as a potential high temperature superconductor. Fundamental interest originates from its very small atomic mass and the internal degrees of freedom of the hydrogen molecule (H2), which permit a wide variety of quantum phases with various types of order. Hydrogen phases have previously been controlled through high pressure, as well as the presence of a surface.
Here we report direct evidence of a new phase of H2 observed only when the hydrogen is adsorbed on the surface of a particular porous carbon material. A phase transition is observed in hydrogen adsorption isotherms and neutron scattering experiments at temperatures between 74-101 K. These temperatures are much higher than the critical temperature of bulk H2 at 33 K, and while surfaces have been known to raise phase transition temperatures, the increase observed here is many times larger than in previous systems. We show how the transition temperature of the fluid to commensurate solid phase may be significantly raised in a material with properties consistent with the porous carbon. We also discuss several of the more unusual experimental results, such as the presence of both an upper and lower temperature bound, which suggest some type of exotic phase ordering to be probed by future work. An application of this phase in hydrogen storage systems is proposed.
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