HR: 1330h
AN: C12A-0864    [PDF]
TI: A Model of Experimental Static Grain Growth in Polycrystalline Fine-grained Ice Ih
AU: * McDaniel, S
EM: smcdaniel@lanl.gov
AF: University of Washington, Dept of Earth and Space Sciences Box 351310, Seattle, WA 98195 United States
AU: * McDaniel, S
EM: smcdaniel@lanl.gov
AF: Los Alamos National Laboratory, Lanl/MS H805, Los Alamos, NM 87545 United States
AU: Waddington, E
EM: edw@ess.washington.edu
AF: University of Washington, Dept of Earth and Space Sciences Box 351310, Seattle, WA 98195 United States
AU: Bennett, K
EM: kristin.bennett@science.doe.gov
AF: US Dept of Energy - Office of BES, GTN/SC-13/F419 1000 Independence Ave, SW, Washington, DC 20585 United States
AU: Durham, W
EM: durham1@llnl.gov
AF: Lawrence Livermore National Laboratory, 7000 East Ave, Livermore, CA 94550 United States
AB: A key to understanding the dynamic behavior of ice, both in planetary and terrestrial conditions, is a fundamental comprehension of flow mechanisms. The course of deformation in ice gives rise to dynamic recrystallization and other processes, leading to changing grain sizes, which is predicted to reach steady state over geologic time periods. Deformation and flow of polycrystalline ice crystals in ice sheets and glaciers depends strongly on crystal size and temperature. In order to help understand grain-size effects on flow, we performed laboratory experiments on fine-grained, polycrystalline ice Ih samples to investigate the effect of temperature on the rate of grain growth in statically annealed ice. Temperature was varied from 220-240K. Ice samples were placed inside the bath for 1-75 hours to examine the effect of time and temperature on grain growth, grain-size distribution, and grain orientation. Low-temperature scanning electron microscopy (SEM) was used to measure grain size and growth. Grain size distribution histograms are compiled to examine the rate at which the small grains shrink and the large grains grow. To extract information about the microphysics of grain growth, analysis criteria focus on a variety of physical properties, such as size, grain boundary curvature, and physical interaction of grains with neighbors. While it is known that some grains grow at the expense of others, it remains uncertain what properties control this action. A model based on experimental data extracted from SEM images is developed to determine laws for grain growth and shrinkage. The importance of energy changes among grains, and whether crystal energy is a significant criterion for grain growth and ultimately in which grains grow and which shrink during static growth, is suggested. The results are significant in establishing grain growth rates under ambient conditions and temperatures applicable to natural ice settings, such as in glaciers and ice sheets.
DE: 5199 General or miscellaneous
SC: Cryosphere [C]
MN: 2003 Fall Meeting