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