 |
| Titel |
Deformation and microstructure of coarse- and fine-grained pure water ice |
| VerfasserIn |
Sabrina Diebold, William B. Durham, Dave J. Prior, Rachel W. Obbard, Ian Baker, Laura Stern |
| Konferenz |
EGU General Assembly 2011
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250054756
|
|
|
|
|
|
| Zusammenfassung |
| In the outer solar system, water ice is abundant. It is the dominant constituent of icy moons
and Kuiper belt objects. In order to better understand the dynamic processes on icy
moons, good knowledge of the rheology of water ice is essential. We focus on the
influence of grain growth on the deformation behavior of ice. By understanding grain
growth in combination with deformation mechanisms, it is possible to reconstruct
thermal evolutions and tectonic histories of icy moons. Grain growth is expected to
influence the evolution of strength of ice by altering the relative contributions to
strain rate by grain-size-sensitive (GSS) creep mechanisms, such as diffusion and
grain-boundary sliding, and grain-size-insensitive (GSI) creep mechanisms, such
as dislocation creep. We performed different types of experiments, including the
preparation of fine-grained ice and the deformation of coarse- and fine-grained ice
aggregates. To make fine-grained ice, we applied a pressure release technique resulting in
phase changes. First, coarse-grained ice phase I was transferred to ice phase II
by applying a confining pressure of around 245 MPa. The sample was exposed
to this high confining pressure for approximately 15 minutes to assure full phase
transformation. Then, the confining pressure was released as quickly as possible, resulting in
nucleation of fine-grained ice phase I grains. These so called pressure-drop experiments
can be performed in a special cryogenic Heard-type deformation apparatus. After
repeating the pressure-drop procedure three times, the fine-grained ice powder material
was cold-pressed, resulting in dense ice aggregates. The deformation experiments
were performed at temperatures between 190 K and 240 K, at confining pressures
between 30 MPa and 100 MPa, and at strain rates between 1E-08/s and 1E-04/s.
We produced orientation maps of the undeformed fine-grained ice using electron
backscatter diffraction in a scanning electron microscope. These show that during the
back-transformation from ice II to ice I, the newly formed Ice I grains form clusters
which share a c-axis orientation, pre-defined by their relationship to the previous
rhombic ice II crystal lattice. Mechanical results of deformed coarse-grained samples
show that dislocation creep is the dominant deformation mechanism resulting in
grain size reduction caused by dynamic recrystallization. Fine-grained ice samples
show grain-size-sensitive creep behaviour, which is affected by grain growth of
grains at higher temperatures. For both coarse-grained and fine-grained samples,
microstructures seen on SEM images support the interpretation of the mechanical results. |
|
|
|
|
|
|