Physics – Geophysics
Scientific paper
Oct 1990
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990tela.rept.....n&link_type=abstract
M.S. Thesis Tel-Aviv Univ. (Israel). Dept. of Geophysics and Planetary Sciences.
Physics
Geophysics
Amorphous Materials, Comet Nuclei, Crystal Growth, Crystal Lattices, Crystal Structure, Gas Evolution, Ice, Ice Formation, Trapping, Gas-Solid Interactions, Gaseous Diffusion, Sublimation, Vapor Pressure
Scientific paper
The structure and thermal evolution of amorphous ice, trapping of gases in the ice, and their release from it have been studied. The release of gas from the ice during the transformation from amorphous to cubic structure, the transformation from cubic to hexagonal structure and the sublimation of ice were examined. It was found that the amount of gas remaining in the ice after the transformation to cubic structure depends linearly on the ice thickness. Reduction of the gas:water-vapor ratio in the deposition mixture, and thus the amount of gas trapped in the ice, caused a greater decrease in the amount of gas released during the amorphous to cubic transformation than during the cubic to hexagonal transformation and during sublimation. During the transformation from amorphous to cubic structure, part of the gas is released and part penetrates into deeper layers, even if these comprise mostly hexagonal ice. The gas is probably trapped in amorphous regions in those layers and is released during their transformation from the cubic to the hexagonal structure. The gas which is released during sublimation is apparently trapped during the deposition process. It is possible that part of this gas release is due to the decomposition of clathrate-hydrate. A large amount of frozen gas in the ice affects the ice structure during the deposition process, by preventing the formation of a closed structure. Thus, most of the gas is released during the transformation from amorphous to cubic ice and from the cubic to the hexagonal structure.
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