Compression Freezing Kinetics of Water to Ice VII

Time-resolved x-ray diffraction (XRD) of compressed liquid water shows transformation to ice VII in 6 nsec, revealing crystallization rather than amorphous solidification during compression freezing. Application of classical nucleation theory indicates heterogeneous nucleation and one-dimensional (e.g., needlelike) growth. These first XRD data demonstrate rapid growth kinetics of ice VII with implications for fundamental physics of diffusion-mediated crystallization and thermodynamic modeling of collision or impact events on ice-rich planetary bodies.

Figure 1

Experimental configuration of the XFEL probe and optical laser. The shock freezing behavior of water captured in a Debye-Scherrer geometry. Inset: Schematic of target package as a cut away side view.

Figure 2

Multiplot of time-resolved x-ray diffraction data. Dark subtracted raw diffraction data plotted without any additional normalization. Traces are offset for visual clarity. Ice VII (110) and (200) peaks are marked with asterisks. Au (111), (200), and (220) peak position trends are marked with dashed grey lines. Au is used to estimate pressure for traces between 7.5–13.2 ns (Refs. [32, 33]). Samples for the last two traces, 17.2 and 18.9 ns, did not have a Au coating; therefore, pressures (denoted with $^$) are estimate from the ice VII equation of state [5]. Breaks in the detector are seen at $2\theta$ of 43.5°, 49.5°, and 61°. Inset: Example of Rietveld refinement performed on run 130 showing good agreement between the observed and calculated patterns.

Figure 3

VISAR spatially averaged lineout. An average of the central $100\mu \mathrm{m}$ region of the apparent velocity histories. Colored bars (matched to Fig. 2 traces) indicate XFEL probe time where width of the bar includes the $+/-350\mathrm{ps}$ timing uncertainty.

Figure 4

Phase diagram of ${\mathrm{H}}_2\mathrm{O}$ and trend in volume fraction converted to ice VII in explored phase space. (a) Equilibrium phase diagram of ${\mathrm{H}}_2\mathrm{O}$ (Ref. [45]) and Hugoniot (dashed trace) and isentrope (grey trace) curves from IAPWS95 liquid equation of state [32]. Colored points show coverage of phase space accessed in this work with the (b) fraction converted to ice VII (${\alpha }_{\text{ice}VII}$, red points; blue point is starting time-zero fraction, not included in the fit). Best JMAK model fit (red curve) is compared to other combinations of JMAK parameters (grey curves).