Creating ice in nanoseconds
Daniel Dolan has used
Sandia’s Z machine to compress
water into ice at extreme
pressures and temperatures.
Photo by Bill Doty
“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].”
In a recent Z machine experiment, the volume
of water shrank abruptly and discontinuously,
consistent with the formation of almost every
known form of ice.* “This work,” says Dolan,
“is a basic science study that helps us understand
materials at extreme conditions.”
* One might wonder — given the common
experience of frozen water expanding to
wreck garden hoses left outside over winter
— why this ice shrank instead of expanding.
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.
But the experiment also has potential practical
value. The work, published in the May issue
of
Nature Physics¹, was undertaken partly because
phase diagrams that predict water’s state
at different temperatures and pressures are
not always correct. This fact is worrisome to
experimentalists working at extreme conditions
and those having to work at distances, where
direct measurement is impractical.
For example, work reported some months
ago at the Z machine demonstrated that
nanoseconds astronomers’ ideas about the state of water on
the planet Neptune were probably incorrect.
(Sandia Technology, Vol. 8, No. 4, Winter
2006/2007.) Closer at hand, water in a glass
can be cooled below freezing and remain a
liquid, in what is called a supercooled state.
Avoiding failures
Accurate knowledge of water’s behavior is
potentially important for the Z machine’s
operation because its water acts as an insulator
and switch. Now that the machine has been
newly 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 new machine or even more
powerful successors, should those be built.
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