On the hysteresis loop and equilibrium transition in slit-shaped ink-bottle pores
- PDF / 2,243,856 Bytes
- 18 Pages / 595.276 x 790.866 pts Page_size
- 78 Downloads / 203 Views
On the hysteresis loop and equilibrium transition in slit-shaped ink-bottle pores Nikom Klomkliang • D. D. Do • D. Nicholson
Received: 8 April 2013 / Accepted: 14 August 2013 / Published online: 28 August 2013 Ó Springer Science+Business Media New York 2013
Abstract Bin grand canonical Monte Carlo simulations have been carried out to study adsorption–desorption of argon at 87.3 K in a model ink-bottle mesoporous solid in order to investigate the interplay between the pore blocking process, controlled by the evaporation through the pore mouth via the meniscus separating the adsorbate and the bulk gas surroundings, and the cavitation process, governed by the instability of the stretched fluid (with a decrease in pressure) in the cavity. The evaporation mechanism switches from pore blocking to cavitation when the size of the pore neck is decreased, and is relatively insensitive to the neck length under conditions where cavitation is the controlling mechanism. We have applied the recentlydeveloped Mid-Density scheme to determine the equilibrium branch of the hysteresis loop, and have found that, unlike ideal simple pores of constant size and infinite length, where the equilibrium transition is vertical, the equilibrium branch of an ink-bottle pore has three distinct sub-branches within the hysteresis loop. The first subbranch is steep but continuous and is close to the desorption branch (which is typical for a pore with two open ends); this is associated with the equilibrium state in the neck. The third sub-branch is much steeper and is close to the adsorption branch (which is typical for either a pore with one end closed or a closed pore), and is associated with the equilibrium state in the cavity. The second subbranch, connecting the other two sub-branches, has a more N. Klomkliang D. D. Do (&) D. Nicholson School of Chemical Engineering, University of Queensland, St. Lucia, Brisbane, QLD 4072, Australia e-mail: [email protected] N. Klomkliang School of Chemical Engineering, Suranaree University of Technology, Nakhon Ratchasima 30000, Thailand
gradual slope. The domains of these three sub-branches depend on the relative sizes of the cavity and the neck, and their respective lengths. Our investigation of the effects of changing neck length clearly demonstrates that cavitation depends, not only on fluid properties, as frequently stated, but also on pore geometry. Keywords Adsorption Ink-bottle pores Hysteresis Pore blocking Cavitation Equilibrium transition
1 Introduction The bottle shaped model holds a special place in discussions of adsorption in porous materials. The model was first proposed by McBain (1935) (who originated the term inkbottle) as a possible explanation for the existence of hysteresis in the adsorption desorption isotherm. In McBain’s theory, filling continued after adsorbate had condensed in the narrow neck because adsorbate liquid was driven into the pore by increasing pressure (Sing et al. 1985). As pressure was lowered again through the desorption branch, the wide body remained fil
Data Loading...
