Effects of insoluble particles on grain growth in polycrystalline ice: Implications for rheology of ice shells of icy satellites

Details Effects of insoluble particles on grain growth in polycrystalline ice: Implications for rheology of ice shells of icy satellites Effects of insoluble particles on grain growth in polycrystalline ice: Implications for rheology of ice shells of icy satellites

Dec 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p21b1221k&link_type=abstract

American Geophysical Union, Fall Meeting 2009, abstract #P21B-1221

Physics

[3902] Mineral Physics / Creep And Deformation, [5422] Planetary Sciences: Solid Surface Planets / Ices, [6015] Planetary Sciences: Comets And Small Bodies / Dust, [6045] Planetary Sciences: Comets And Small Bodies / Physics And Chemistry Of Materials

Scientific paper

Recently, grain-size sensitive creep was found in both ice Ih (Goldsby and Kohlstedt, JGR 2001) and ice II (Kubo et al., Science 2006), and under low-stress conditions (˜0.01-0.1 MPa) in the interiors of icy satellites, the grain-size sensitive creep mechanism is probably dominant as compared to the dislocation creep mechanism. Because the ice viscosity in the grain-size sensitive creep regime strongly depends on grain size, it is important to study on the kinetic processes controlling the ice grain size. It has been observed that pinning by insoluble dust particles actually plays a major role in the grain-size reduction in terrestrial ice sheets (Durand et al., JGR 2006). Silicate dust is believed to be one of the major impurities present in ice shells of icy satellites. In the present study, grain growth experiments were carried out on polycrystalline ice containing insoluble particles, and effects of small volume fractions of second-phase particles with different particle sizes on the ice grain growth were examined (Kubo et al., JMPS 2009). We carried out four sets of grain growth experiments at 270 K using different starting materials: pure ice and ice containing approximately 1 vol% of insoluble particles of 115-μm soda glass, 18-μm alumina, and 2-μm silica. Microstructures of the polycrystalline ice samples were observed by using an optical microscope in transmitted and reflected light after etching the grain boundaries. Significant grain growth was observed in the pure ice sample. On the other hand, the presence of approximately 1 vol% of the second-phase particles was found to significantly inhibit the grain growth, and this inhibition effect strongly depends on particle size. The insoluble particles are located at grain boundaries and triple junctions and also in the grain interior. The observed grain growth behavior of ice can be reasonably interpreted on the basis of the Zener pinning effect (e.g., Monohar et al., 1998). Our preliminary results suggest that low viscosities due to small grain sizes required for convective instability in ice shells of icy satellites are achieved by the presence of very small fractions of fine silicate dust particles.

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