News on “Metallic water”

by Astronuc
Tags: news, water”, “metallic
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Oct13-06, 03:17 PM
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Phase diagram of water revised by Sandia researchers - Press Release Oct 3, Sandia National Lab, Albuquerque, NM

“Metallic water” alters characteristics of Neptune and impacts other physics

Supercomputer simulations by two Sandia researchers have significantly altered the theoretical diagram universally used by scientists to understand the characteristics of water at extreme temperatures and pressures.

The new computational model also expands the known range of water’s electrical conductivity.

The Sandia theoretical work showed that phase boundaries for “metallic water” — water with its electrons able to migrate like a metal’s — should be lowered from 7,000 to 4,000 kelvin and from 250 to 100 gigapascals.

(A phase boundary describes conditions at which materials change state — think water changing to steam or ice, or in the present instance, water — in its pure state an electrical insulator — becoming a conductor.)

The lowered boundary is sure to revise astronomers’ calculations of the strength of the magnetic cores of gas-giant planets like Neptune. Because the planet’s temperatures and pressures lie partly in the revised sector, its electrically conducting water probably contributes to its magnetic field, formerly thought to be generated only by the planet’s core.

The calculations agree with experimental measurements in research led by Peter Celliers of Lawrence Livermore National Laboratory.

Sandia is a National Nuclear Security Administration laboratory.

How the work came about

Surprising results were not the intent of Sandia co-investigators Thomas Mattsson and Mike Desjarlais.

“We were trying to understand conditions at [a powerful Sandia accelerator known as] Z,” says Mattsson, a theoretical physicist, “but the problems are so advanced that they hopscotched to another branch of science.”

. . . .

Mattsson and Desjarlais first found the standard water-phase diagram out of whack when they ran an advanced quantum molecular simulation program on Sandia’s Thunderbird supercomputer that included “warm” electrons instead of unrealistic cold ones, says Desjarlais.

The molecular modeling code VASP (Vienna Ab-initio Simulation Package), based on density functional theory (DFT), was written in Austria. Desjarlais extended it to model electrical conductivity and Mattsson developed a model for ionic conductivity based on calculations of hydrogen diffusion. An accurate description of water requires this combined treatment of electronic and ionic conductivity.

The adaptation of VASP to high-energy-density physics (HEDP) work at Sandia was motivated by earlier experimental measurements of the conductivity of exploding wires by Alan DeSilva at the University of Maryland. DeSilva found a considerable disparity between his data and theoretical models of materials in the region of phase space called warm dense matter. Desjarlais’ early VASP conductivity calculations immediately resolved the discrepancy. In recent years, a team of Sandia researchers has been extending one of Sandia’s own DFT codes (Socorro) to go beyond the capabilities of VASP for HEDP applications.

. . . .
Very interesting work in both computational and experimental physics. High-energy-density physics (HEDP) is a relatively new area, with relevance to thermonuclear reactions (e.g. stars and related natural phenomena, and nuclear weapons), and propulsion and energy production systems.
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LURCH is offline
Oct14-06, 08:23 AM
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Do you think it will be possible to verify these results experimentally? I've heard of a device that uses two diamond-tipped cylindres to compress merials in between the cylinders (I think it was called a " diamond anvil"). Last I heard, this device was being used to study metallic water and solid metallic hydrogen. Would it be possible to study phase transition with this device?
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Oct14-06, 08:43 AM
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Here is some background on the Diamond Anvil Pressure Cell, which has been around for a while. -

A wikipedia article - - claims "The range of static pressure attainable today extends to the pressures prevailing in the earth’s center (~360 GPa)," so it might be possible to achieve the pressures of 100-250 GPa.

The matter of the temperature "4,000 K" (3737°C) is a problem, or a challenge. Very few materials can withstand such temperatures, but perharps the water could be heated with a laser, which means the diamond would be at 4000 K, and the mandrels would need to be cabides of W, Ta, Hf or similar metal.

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