Rapid freezing of water under dynamic compression

Abstract

Understanding the behavior of materials at extreme pressures is a central issue in fields like aerodynamics, astronomy, and geology, as well as for advancing technological grand challenges such as inertial confinement fusion. Dynamic compression experiments to probe high-pressure states often encounter rapid phase transitions that may cause the materials to behave in unexpected ways, and understanding the kinetics of these phase transitions remains an area of great interest. In this review, we examine experimental and theoretical/computational efforts to study the freezing kinetics of water to a high-pressure solid phase known as ice VII. We first present a detailed analysis of dynamic compression experiments in which water has been observed to freeze on sub-microsecond time scales to ice VII. This is followed by a discussion of the limitations of currently available molecular and continuum simulation methods in modeling these experiments. We then describe how our phase transition kinetics models, which are based on classical nucleation theory, provide a more physics-based framework that overcomes some of these limitations. Finally, we give suggestions on future experimental and modeling work on the liquid-ice VII transition, including an outline of the development of a predictive multiscale model in which molecular and continuum simulations are intimately coupled.

Melting and refreezing of zirconium observed using ultrafast x-ray diffraction

“…The first is adiabatic cooling due to the release of pressure in a thermally isolated cell. Its initial temperature may be T m if crystal seeds are present or is much lower, down to 0.7T m if homogeneous nucleation is possible [32,33]. The seeded or nucleated crystals grow until the supercooling falls to zero.…”

Nanosecond Freezing of Water at High Pressures: Nucleation and Growth near the Metastability Limit

“…The dynamic compression experiments have employed one of two techniques (see our review paper [18]): multiple-shock or ramp compression. In both techniques, a thin water sample sandwiched between two thicker solid windows is compressed from ambient conditions along the quasi-isentrope into the ice VII region of the phase diagram (Fig-ure 1).…”

“…Ice VII is a cubic high-pressure solid phase discovered over 80 years ago [19] that may be present in oceanic super-Earths [16,17] and even in the Earth's mantle [20]. No theoretical model developed to date has been able to reproduce the rapid (sub-microsecond) liquid/ice VII transition kinetics observed in any of the experiments [18].…”

“…where B homo is a pre-exponential factor that re- flects the number of available nucleation sites, ∆G * homo is the nucleation energy barrier, k B is the Boltzmann constant, and T is the temperature [18]. Details regarding quantities like B homo and ∆G * homo are summarized in the Supplemental Material (SM).…”

“…Our models correctly predict that freezing does not occur under these conditions. In contrast, previously published simulations of these "null result" experiments have artificially disallowed freezing by removing the ice VII phase from their EOS (i.e., running liquid-only models), rather than allowing a model of the kinetics to determine the final state [9,[11][12][13]18]. The ability to reproduce this null result is an important test of our CNT-based framework, and we show in the SM that it successfully reproduces similar experiments from Dolan and Gupta et al [9] and Stafford et al [13] We have explained how a theoretical framework built on CNT and growth, when combined with hydrodynamics simulations, provides quantitative agreement with experimental pressure wave profiles associated with nanosecond freezing kinetics of liquid water to ice VII via homogeneous nucleation.…”