The Formation of Ice VI Under Static Pressure

1
The Formation of Ice VI Under Static Pressure
H.K. Ploeg1, M.D. McCluskey2,3, G.J.
Hanna2,3 1The University of Michigan, Ann Arbor,
MI 2 Institute for Shock Physics, Washington
State University, Pullman, WA 3Dept. of Physics
and Astronomy, Washington State University,
Pullman, WA
Phase Change
Procedure The diamond anvil cell is illustrated
below. Because the diamonds have a small contact
area, a small force creates a very large
pressure. Turning the screws on the cell
increases the pressure on the sample. The sample
consists of water and a small ruby chip for
measuring the pressure. The metal gasket
enclosing the sample is made of beryllium copper.
(The anvils used in this experiment are actually
moissanite.)
Starting from ambient pressure, keeping the
temperature constant at 294 K, the pressure is
slowly increased until a phase change is observed
at about 9.8kbar. The phase diagram (left)
confirms that the cell contains ice VI. The
entire sample freezes to ice VI in under a
second after the phase change the sample appears
the same as before. Reducing the pressure
melts the sample melting takes about 90 minutes.
Water Becoming Ice VI
The ice begins to form on the outer ring of the
sample and progresses towards the center. The
entire sample is converted to ice VI in less than
a second (right). The ruby chip is visible in the
upper left of the sample.
t 0
t 0.04 s
t 0.67 s
t 0.17 s
0.66 mm
Ice VI Becoming Water
The first slide is solid ice VI at a pressure
near 10kbar. After the pressure is slowly
released the ice cracks and the phase change
begins. The pressure continues to drop inside
the gasket. The ice breaks up into smaller pieces
that coalesce into larger ones, but the total
mass of the ice gets smaller. Eventually only
liquid water remains.
Citations
M. Chakroun and O. Grasset, Journal of Chemical
Physics 127, 124506 (2007)
t 0
t 0.04 s
t 81 s
t 921 s
t 1521 s