http://www.technologynewsdaily.com/node/6340

Ice Created In Nanoseconds

Submitted by Technology News... on Fri, 2007-03-16 14:51.

Sandia’s huge Z machine, which generates temperatures hotter than the
sun, has turned water to ice in nanoseconds.

However, don’t expect anything commercial just yet: the ice is hotter
than the boiling point of water.

“The three phases of water as we know them — cold ice, room temperature
liquid, and hot vapor — are actually only a small part of water’s
repertory of states,” says Sandia researcher Daniel Dolan. “Compressing
water customarily heats it. But under extreme compression, it is easier
for dense water to enter its solid phase [ice] than maintain the more
energetic liquid phase [water].”

Sandia is a National Nuclear Security Administration (NNSA) laboratory.

In the Z experiment, the volume of water shrank abruptly and
discontinuously, consistent with the formation of almost every known
form of ice except the ordinary kind, which expands. (One might wonder
why this ice shrank instead of expanding, given the common experience of
frozen water expanding to wreck garden hoses left out over winter. The
answer is that only “ordinary” ice expands when water freezes. There are
at least 11 other known forms of ice occurring at a variety of
temperatures and pressures.)

“This work,” says Dolan, “is a basic science study that helps us
understand materials at extreme conditions.”

But it has potential practical value. The work, which appears online
March 11 in Nature Physics, was undertaken partly because phase diagrams
that predict water’s state at different temperatures and pressures are
not always correct — a fact worrisome to experimentalists working at
extreme conditions, as well as those having to work at distances where
direct measurement is impractical. For example, work reported some
months ago at Z demonstrated that astronomers’ ideas about the state of
water on the planet Neptune were probably incorrect.

Closer at hand, water in a glass could be cooled below freezing and
remain water, in what is called a supercooled state.

Accurate knowledge of water’s behavior is potentially important for Z
because the 20-million-ampere electrical pulses the accelerator sends
through water compress that liquid. Ordinarily, the water acts as an
insulator and as a switch. But because the machine is being refurbished
with more modern and thus more powerful equipment, questions about
water’s behavior at extreme conditions are of increasing interest to
help avoid equipment failure for the machine or its more powerful
successors, should those be built.

One unforeseen result of Dolan’s test was that the water froze so
rapidly. The freezing process as it is customarily observed requires
many seconds at the very least.

The answer, says Dolan, seems to be that very fast compression causes
very fast freezing. At Z and also at Sandia’s nearby STAR (Shock
Thermodynamic Applied Research) gas gun facility, thin water samples
were compressed to pressures of 50,000-120,000 atmospheres in less than
100 nanoseconds. Under such pressures, water appears to transform to ice
VII, a phase of water first discovered by Nobel laureate Percy Bridgman
in the 1930s. The compressed water appeared to solidify into ice within
a few nanoseconds.

Ice VII has nothing to do with ice-nine, an entirely fictional creation
of author Kurt Vonnegut in his 1963 novel Cat’s Cradle. There, a few
molecules of the invented substance acts as a precipitating seed to
cause an extended chemical reaction that freezes almost all of Earth’s
water. Ice VII, on the other hand, only stays frozen as long as it is
under enormous pressure. The pressure relenting, the ice changes back to
ordinary water.

Nucleating agents, of course, are often used to hasten sluggish chemical
processes, such as when clouds are “seeded” with silver iodide to induce
rain. Dolan already had demonstrated, as a graduate physics student at
Washington State University, that water can freeze on nanosecond time
scales in the presence of a nucleating agent.

However, the behavior of pure water under high pressure remained a
mystery.

Sandia instruments observed the unnucleated water becoming rapidly
opaque — a sign of ice formation in which water and ice coexist — as
pressure increased. At the 70,000 atmosphere mark and thereafter, the
water became clear, a sign that the container now held entirely ice.

“Apparently it’s virtually impossible to keep water from freezing at
pressures beyond 70,000 atmospheres,” Dolan says.

For these tests, Z created the proper conditions by magnetic
compression. Twenty million amperes of electricity passed through a
small aluminum chamber, creating a magnetic field that isentropically
compressed aluminum plates roughly 5.5 by 2 inches in cross section.
This created a shockless but rapidly increasing compression across a
25-micron-deep packet of water.

The multipurpose Z machine, whose main use is to produce data to improve
the safety and reliability of the US nuclear deterrent, has compressed
spherical capsules of hydrogen isotopes to release neutrons — the
prerequisite for controlled nuclear fusion and essentially unlimited
energy for humanity.

This work is sponsored by the NNSA. Other authors on the paper are Chris
Deeney (now at NNSA), and Sandians Mark Knudson and Clint Hall.

But it has potential practical value. The work, which appears online
March 11 in Nature Physics, was undertaken partly because phase diagrams
that predict water=3Fs state at different temperatures and pressures are
not always correct =3F a fact worrisome to experimentalists working at
extreme conditions, as well as those having to work at distances where
direct measurement is impractical. For example, work reported some
months ago at Z demonstrated that astronomers=3F ideas about the state of
water on the planet Neptune were probably incorrect.