A macrothermodynamic approach to the limit of reversible capillary condensation.
The threshold of reversible capillary condensation is a well-defined thermodynamic property, as evidenced by corresponding states treatment of literature and experimental data on the lowest closure point of the hysteresis loop in capillary condensation-evaporation cycles for several adsorbates. The nonhysteretical filling of small mesopores presents the properties of a first-order phase transition, confirming that the limit of condensation reversibility does not coincide with the pore critical point. The enthalpy of reversible capillary condensation can be calculated by a Clausius-Clapeyron approach and is consistently larger than the condensation heat in unconfined conditions. Calorimetric data on the capillary condensation of tert-butyl alcohol in MCM-41 silica confirm a 20% increase of condensation heat in small mesopores. This enthalpic advantage makes easier the overcoming of the adhesion forces by the capillary forces and justifies the disappearing of the hysteresis loop.
Trens
Philippe
P
Laboratoire de Matériaux Catalytiques et Catalyse en Chimie Organique, UMR 5618 CNRS-ENSCM-UM1, Institut C. Gerhardt, FR 1878, ENSCM, 8 rue Ecole Normale, 34296 Montpellier, France.
Tanchoux
Nathalie
N
Galarneau
Anne
A
Brunel
Daniel
D
Fubini
Bice
B
Garrone
Edoardo
E
Fajula
François
F
Di Renzo
Francesco
F