Abstract
The properties of some forms of water ice reserve still intriguing surprises. Besides the several stable or metastable phases of pure ice, solid mixtures of water with gases are precursors of other ices, as in some cases they may be emptied, leaving a metastable hydrogen-bound water structure. We present here the first characterization of a new form of ice, obtained from the crystalline solid compound of water and molecular hydrogen called C0-structure filled ice. By means of Raman spectroscopy, we measure the hydrogen release at different temperatures and succeed in rapidly removing all the hydrogen molecules, obtaining a new form of ice (ice XVII). Its structure is determined by means of neutron diffraction measurements. Of paramount interest is that the emptied crystal can adsorb again hydrogen and release it repeatedly, showing a temperature-dependent hysteresis.
Highlights
The properties of some forms of water ice reserve still intriguing surprises
Only two experimental studies[18,19] have investigated the phase diagram of the H2–H2O compounds at intermediate pressures and have demonstrated the presence of a further stable phase, named C0, at temperatures 100–270 K and pressures 360–700 MPa, which is intermediate between the stability region of the sII clathrate and C1 phase
We discover that the C0 structure is metastable at room pressure even when emptied and is a new form of ice, namely ice XVII
Summary
The properties of some forms of water ice reserve still intriguing surprises. Besides the several stable or metastable phases of pure ice, solid mixtures of water with gases are precursors of other ices, as in some cases they may be emptied, leaving a metastable hydrogen-bound water structure. One experimental study has recently demonstrated, that at least one of these clathrate structures can be emptied of its guests, by letting neon atoms diffuse out of the solid, and persist in a metastable state if preserved at low temperature[3] These and other similar lowdensity lattices of water molecules have raised recently large interest from a theoretical point of view, because they are believed to be the stable phase of solid water at negative pressure[4]. The first in order of increasing pressure, stable at P4100 MPa and at 4–6 °C below 0, is a clathrate hydrate[5,6] having the so-called cubic sII structure, common to other clathrates with different molecular guests[7] In this nonstoichiometric compound, hydrogen molecules are trapped in two types of cages with a total hydrogen molar fraction X (X 1⁄4 mol(H2)/mol(H2O)) up to B35%. As a matter of fact, we show in this work that ice XVII can adsorb and release hydrogen gas over and over, without evident change of structure
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
