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Coadsorption phase diagram for CH_4/CCl_4 on graphite

Weber, William J. and Goodstein, David L. (2006) Coadsorption phase diagram for CH_4/CCl_4 on graphite. Physical Review B, 73 (19). Art. No. 195424. ISSN 1098-0121. doi:10.1103/PhysRevB.73.195424.

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We present an extensive thermodynamic study of methane coadsorbed on graphite precoated with a saturated monolayer of carbon tetrachloride. A combination of heat capacity and volumetric equation of state data permit construction of the multilayer coadsorption phase diagram between 70 and 115 K. Displacement of the preadsorbed CCl_4 by CH_4 occurs by a continuous process across the temperature range studied. While the continuous nature of the transition implies a single phase mixed film during displacement, the observation of a commensurability transition characteristic of CH_4 on bare graphite suggests the emergence of order in the coadsorbed CH_4 in the early stages of displacement. At low temperatures and multilayer coverages, the coadsorption phase diagram shows small but measurable differences from the pure CH_4 data, indicating that the multilayer film formed after displacement is not identical to that of CH_4 in the absence of CCl_4. At higher temperatures, a new first order phase transition is observed to correspond with the completion of displacement. One interpretation is that the phase boundary represents the melting of a nearly pure CH_4 monolayer solid into a mixed liquid film phase, with the size of the melting point depression indicating a concentration of nearly 1% CCl_4 in the liquid phase.

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Alternate Title:Coadsorption phase diagram for CH4/CCl4 on graphite
Additional Information:©2006 The American Physical Society (Received 17 January 2006; published 30 May 2006)
Subject Keywords:organic compounds; graphite; carbon compounds; adsorbed layers; coatings; monolayers; adsorption; phase diagrams; specific heat; equations of state; surface phase transformations; melting; melting point; chemical analysis
Issue or Number:19
Record Number:CaltechAUTHORS:WEBprb06
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:3676
Deposited By: Archive Administrator
Deposited On:26 Jun 2006
Last Modified:08 Nov 2021 20:11

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