Melting curve of H₂O to 90 GPa measured in a laser-heated diamond cell

Abstract

We report new data on the melting curve of H2O in the range 20–90 GPa and 1000–2400 K obtained in a laser-heated diamond anvil cell. We found a marked discrepancy between our present results and previous work which covered the pressure range up to 38 GPa. The melting curve shows a discontinuous change in slope at about 43 GPa, indicating a first-order phase transition most likely to the ice X phase. We could find no evidence for a strong dissociation of H2O up to 200 K above the melting temperatures.

Simultaneous high-pressure and high-temperature volume measurements of ice VII and its thermal equation of state

“…The resulting melting temperatures from the thermodynamic calculation was compared with experimentally determined melting curves based on various types of melting criteria such as electrical resistance, XRD, Raman spectroscopy, and optical observations. [18][19][20][21][22][23][24][25][26] …”

The Reactivity of Energetic Materials at Extreme Conditions

“…This has lead to theoretical investigations of the water phase diagram 50 , in which Car-Parrinello Molecular Dynamics (CPMD) simulations 57 were conducted at temperature and pressures ranging from 300 to 7000 K and 30-300 GPa 51 . In these first principles molecular dynamics simulations, the electronic degrees of freedom are treated 52,61 . In addition, extrapolations of the proton diffusion constant of ice into the superionic region were found to be far lower than a superionic criteria of 10 -4 cm 2 /s.…”

Chemistry of H2O and HF under Extreme Conditions

“…The density profiles of large planets, such as Uranus and Neptune, suggest that there exists within a thick layer of "hot ice", which is thought to be 56% H 2 O, 36% CH 4 , and 8% NH 3 [12]. This has lead to theoretical investigations of the water phase diagram [2], in which Car-Parrinello Molecular Dynamics (CPMD) simulations [13] were conducted at temperature and pressures ranging from 300 to 7000K and 30-300 GPa [3].…”

“…The fluid high pressure phase has been recently confirmed by X-ray diffraction results of water melting at ca. 1000K and up to 40 GPa pressure [18,19,20]. In addition, extrapolations of the proton diffusion constant of ice into the superionic region were found to be far lower than a superionic criteria of 10 4 cm 2 ¡ s£ [21] Thus, it is clear there is great need for further work to resolve the apparently conflicting data.…”

“…However, the existence of superionic solid phases of hydrogen bonded compounds had been theorized previously [2,3]. Recent experimental and computational results indicate the presence of a high pressure triple point in the H 2 O phase diagram [4,5,6], including a so-called superionic solid phase with fast hydrogen diffusion [6,7]. Goldman et al have recently described the emergence of symmetric hydrogen bonding in superionic water at 2000 K [7] and 95 GPa.…”