Water exhibiting bizarre metastable phenomena when compressed or cooled rapidly

New research involving scientists at Lawrence Livermore National Laboratory (LLNL) shows that water can remain liquid in a metastable state when transitioning from liquid to a dense form of ice at pressures higher than those previously measured.

Water under extreme conditions has recently gained attention because of its complex phase diagram, including superionic ice phases with exotic properties that exist at high pressures and densities. To date, 20 unique crystalline phases of ice have been found naturally on Earth or in the laboratory. Water also exhibits bizarre metastable phenomena when compressed or cooled very rapidly, which has been of interest to physicists around the world for many years.

“If the water is compressed very quickly, it will remain liquid in a metastable state until it finally crystallizes into Ice VII at a higher pressure than expected,” said Michelle Marshall, researcher at the Energy Laboratory. laser (LLE) from the University. de Rochester, former LLNL postdoctoral fellow and lead author of the study published in Physical examination letters.

Ice VII is the stable polymorph of water at room temperature and at pressures exceeding ∼2 GPa (over 19,000 atmospheres). Recently, Ice VII was found naturally on Earth for the first time as inclusions in diamonds from deep within the mantle. exist within the frozen moons of Jupiter and in the aquatic worlds beyond our solar system.

The new research has shown how water can remain liquid in a metastable state during the liquid-ice-VII transition at pressures higher than those previously measured. Previous experimental work at the giant pulsed power Z facility has shown that compressed water turns into VII ice at 7 GPa (69,000 atmospheres) when the water is ramped over hundreds of nanoseconds. Instead, new experiments have turned to using high-power lasers at the Omega laser facility to compress water on even shorter time scales (nanoseconds).

As in the previous LLNL work on gold (Au) and platinum (Pt), the hardest part is compressing the water gently enough to avoid forming a shock wave that would ruin the experiment (i.e. i.e. achieve a compression ramp without shock). Because water is much more compressible than metals like Au and Pt, creating a compression ramp wave in a micrometer water layer requires increasing the pressure load at a much slower rate.

“Even though the pressures we achieve seem very modest compared to other laser-driven ultra-fast dynamic compression experiments, these extremely difficult experiments are really on the borderline of what we can do with giant lasers, and that was. an exciting challenge, ”said the LLNL scientist. and co-author Marius Millot.

The new data shows that water can remain liquid up to at least 8-9 GPa (79,000-89,000 atmospheres) before crystallizing into ice VII: the freezing pressure increases with the compression ratio.

“This means that water can remain liquid at pressures at least 3.5 times higher than expected based on the equilibrium phase diagram,” Marshall said. “It’s really cool to think that we compress it so fast that the water doesn’t have time to crystallize, so it stays liquid.”

“We’re on the frontier of super-fast experimental science,” Marshall said, “and it was great to collaborate with our colleagues in theory and simulation to get a more detailed picture of what was going on. It’s remarkable. that the most recent theoretical and numerical advances now provide a detailed understanding of the observed phenomena.This could have implications for our general understanding of phase transformations under extreme conditions.

This work is part of a larger effort to understand phase transition kinetics in dynamically compressed materials. The ubiquitous nature of water and its complex phase diagram make the liquid-ice-VII phase transition an interesting test bed for modeling phase transition kinetics. SAMSA, a kinetics model developed by LLNL, provides a detailed understanding of experimental results while building on the fundamentally simple picture of homogeneous nucleation using classical nucleation theory.

Overall, this work improves models and understanding of materials, which could have interesting implications for other key research areas of the Laboratory such as advanced manufacturing and 3D printing. The metastable states and complex crystallization of water are also essential for atmospheric science and therefore for climate security.