Heat capacity of multilayer methane on graphite: Phase transitions in the first four layers
- Condensed Matter Physics 114-36, California Institute of Technology, Pasadena, California 91125 (United States)
We present high-resolution heat-capacity data for methane adsorbed on graphite for nominal coverages of 0.87 to 7 layers, from [ital T]=70 to 120 K. For films thicker than 1.1 layers, we find capillary condensate coexisting with the film. We have performed heat-capacity scans on films formed by both adsorption and desorption. By comparing the locations of the phase transitions in the chemical potential [mu] vs [ital T] plane, we find that there is no significant interaction between the film and the capillary condensate. The heat-capacity signals from the films map out an unexpectedly rich set of phenomena for the second, third, and fourth layers, including a two-dimensional triple point and a liquid-gas coexistence region for each layer. The fourth-layer critical temperature we find is lower than previous values found by vapor-pressure isotherms.
- DOE Contract Number:
- FG03-85ER45192
- OSTI ID:
- 6857429
- Journal Information:
- Physical Review, B: Condensed Matter; (United States), Journal Name: Physical Review, B: Condensed Matter; (United States) Vol. 47:12; ISSN PRBMDO; ISSN 0163-1829
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
360602* -- Other Materials-- Structure & Phase Studies
360606 -- Other Materials-- Physical Properties-- (1992-)
ALKANES
CARBON
ELEMENTAL MINERALS
ELEMENTS
FILMS
GRAPHITE
HYDROCARBONS
METHANE
MINERALS
NONMETALS
ORGANIC COMPOUNDS
PHASE TRANSFORMATIONS
PHYSICAL PROPERTIES
SPECIFIC HEAT
SUBSTRATES
TEMPERATURE RANGE
TEMPERATURE RANGE 0065-0273 K
THERMODYNAMIC PROPERTIES
WETTABILITY