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La surface de la glace : structure, dynamique et interactions : implications astrophysiques

Abstract : In this work, the structure and dynamics of ice surface at low temperature and their different interactions with gases are studied. First, the surface of different kinds of ice is characterized with the help of the comparison between the adsorption properties of nitrogen and argon. For hexagonal ice, the study focused on powders obtained by crushing mnocristals at 77K. We point out the polar character of this type of surface and we analyse the reduction of the adsorption capacities observed after annealing at higher temperature (>190K). A mechanism of water molecules diffusion is suggested to explain these surface evolution kinetics. Then, we show that amorphous ice condensed at 77K has a porous structure, the arrount and the distribution of pores depending on the conditions of condensation. Moreover, it appears that a great instability characterizes these condensates. An interpretation of the properties of these ice condensates is proposed with the aid of the aggregation models. Secondly, a study of CO2 clathrate hydrate formation and decomposition by gas-ice interaction is done at low temperature (about 200K). We point out that a diffusion of water molecules controls the growth of the clathrate structure. For clathrate decomposition, the results suggest a diffusion mechanism of the guest molecules trough the clathrate network and a reorganization of this structure. These different results are applied to two astrophysical problems : In the case of interstellar grains we show that the rate of synthesis of molecular hydrogen is very high on the surface of an amorphous and porous ice grain. For comets , we analyse the different outgassing mechanisms that can occur during the thermal evolution of the nucleus. Particularly, we point out that clathrate hydrate occurence cannot be infered from the gas production observations and we set down the basis of a new type of models for ccmetary nucleus evolutions
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https://tel.archives-ouvertes.fr/tel-00724967
Contributor : Pascale Talour <>
Submitted on : Thursday, August 23, 2012 - 2:41:28 PM
Last modification on : Thursday, November 19, 2020 - 3:54:26 PM
Long-term archiving on: : Friday, December 16, 2016 - 7:59:26 AM

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  • HAL Id : tel-00724967, version 1

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Bernard Schmitt. La surface de la glace : structure, dynamique et interactions : implications astrophysiques. Glaciologie. Université Scientifique et Médicale de Grenoble, 1986. Français. ⟨tel-00724967⟩

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