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Adsorption et Condensation de Fluides Simples dans le Silicium Mesoporeux: Une Approche Experimentale et par Simulation Monte Carlo

Abstract : This work is a study of adsorption/condensation of simple fluids (Ar, Kr, N2) in mesoporous silicon (p-Si). We show by means of transmission electronic microscopy and ion beam analysis that this material presents tubular nanopores, polygonal and asymmetrical-shaped (morphological disorder), and unconnected (no topological disorder). These properties place p-Si in between regular nanopores MCM41 and porous glasses (Vycor). The mean size and the length of p-Si pores are controlled by the parameters of the electrochemical synthesis. The invasion of p-Si by a vapor show the capillary condensation phenomenon and its irreversibility (hysteresis) on the adsorption isotherm curve. Experimental condensation pressures are, for the size of p-Si pores (10-40 nm), lower than that theoretically expected for cylindrical pores. We have performed Monte
Carlo simulations in order to study argon adsorption/condensation at 77 K in pores of various sizes and shapes. The presence of a constriction (extended morphological defect) fundamentally modifies the mechanism of the porefilling and leads to an important lowering of the condensation pressure.We prepare p-Si substrates with pores open at one or at both ends. We show that adsorption isotherms are irreversible in both cases. This result is in contradiction with the Cohan conjecture (validated by our molecular simulations)
which predicts the reversibility for pores open at one end. In addition, the asymmetrical shape of the hysteresis loop is unexpected for an assembly of unconnected mesopores.
Our results obtained for di®erent gazes and pore size distribution seem to indicate that this asymmetrical hysteresis shape is not due to the hypothetic presence of constrictions. Then, we propose that a coupling between pores can occur during the desorption process.
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https://tel.archives-ouvertes.fr/tel-00162504
Contributor : Benoit Coasne <>
Submitted on : Friday, July 13, 2007 - 3:47:52 PM
Last modification on : Thursday, March 11, 2021 - 3:05:03 AM
Long-term archiving on: : Thursday, April 8, 2010 - 11:12:33 PM

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  • HAL Id : tel-00162504, version 1

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Benoit Coasne. Adsorption et Condensation de Fluides Simples dans le Silicium Mesoporeux: Une Approche Experimentale et par Simulation Monte Carlo. Physique [physics]. Université Paris-Diderot - Paris VII, 2003. Français. ⟨tel-00162504⟩

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