Effects of temperature, pore dimensions and adsorbate on the transition from pore blocking to cavitation in an ink-bottle pore

Klomkliang, Nikom; Do, D.D.; Nicholson, D.

doi:10.1016/j.cej.2013.11.019

Cited by 20 publications

(21 citation statements)

References 35 publications

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“…The mechanism of evaporation switches from cavitation-like pore blocking to cavitation when the temperature is increased, behavior typical of ink-bottle pores, where the change in pore size along the axial direction is a step function, 16 and the hysteresis loop changes from type H1 (in the IUPAC classification) at 60 K to a mixture of type H2 (IUPAC) and type C (in the de Boer classification) at 87 K. The sequence of sharp jump and gradual change along the adsorption boundary is due to adsorption in various zones along the pore as seen in Figure 2 where we show snapshots of molecules in a completely filled pore. A zone is defined here as the section of the pore where the packing is commensurate across the pore (giving an integral number of molecular layers).…”

Section: Resultsmentioning

confidence: 99%

“…In the first of these, evaporation occurs from the wide section while the necks remain filled; in the second, molecules in the neck evaporate, resulting in the exposure of the cavity to the bulk gas, and there is consequently an immediate evaporation from the wide section; see references by Sarkisov and Monson, Ravikovithch and Neimark, and Klomkliang et al 15,16,27 for further discussion. A phenomenon described as cavitation-like pore blocking has also been identified in our previous work 10 as a process in which desorption proceeds via a pore blocking mechanism but the desorption branch shows a steep decrease, even though there is no bubble formation in the cavity.…”

Section: Introductionmentioning

confidence: 97%

“…[2][3][4][5][6][7][8][9] However, it is now known that at a given temperature, solids with different pore structures can exhibit similar hysteresis loops [10][11][12] and that their shape can change significantly with temperature. [13][14][15][16] To probe pore structure more effectively, additional information needs to be obtained, and to this end, scanning across the hysteresis loop is proposed as a means of gaining further insight into the structural parameters of the pore network that cannot be deduced from either the adsorption boundary or the desorption boundary of the hysteresis loop. [17][18][19][20][21][22] A desorption scanning curve is obtained when the pressure is decreased on the adsorption boundary, before the upper closure point of hysteresis is reached.…”

Section: Introductionmentioning

confidence: 99%

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Scanning curves in wedge pore with the wide end closed: Effects of temperature

2015

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The desorption scanning curves within the hysteresis loop of argon adsorbed in a wedge-shaped pore with its wide end closed have been studied in the temperature range between 60 and 87 K, using grand canonical Monte Carlo simulation. The distinct features are: (1) adsorbate packing follows a sequence of commensurate regions (zones) and incommensurate regions (junctions); (2) the mechanism for evaporation switches from cavitation-like pore blocking to cavitation when the temperature is increased; as typically observed for ink-bottle pores. When cavitation is the operating mechanism, the descending scanning curve spans across the loop in two stages: a gradual decrease in density in a zone followed by a sharp evaporation from a junction, and then terminates at the lowest point on the vertical cavitation boundary. The adsorption scanning curve proceeds across the loop in two stages complementary to the desorption scanning-curve: a gradual change in density at a junction followed by a sharp change through a zone. Conversely, when cavitation-like pore blocking is operating, the descending curve leaves the adsorption boundary, spans across the hysteresis loop and returns to a different point on the same boundary, rather than to the desorption boundary or to the lower closure point. This feature does not seem to have been recognized in earlier literature and should be considered in the classification of scanning curves.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

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Scanning curves in wedge pore with the wide end closed: Effects of temperature

2015

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“…Experimental isotherms for materials with pores in the mesopore size range exhibit hysteresis at temperatures below the critical hysteresis temperature (T ch ). For a given adsorbate, the properties of the hysteresis loop: shape, size and position, are a function of temperature, pore material and geometry as confirmed in many experimental [4][5][6][7][8][9][10][11] and simulation studies [12][13][14][15][16][17][18][19]. Thus for a given adsorbate, temperature, and an assumed pore model, experimental isotherms can be used in an inversion procedure to determine the pore size distribution of the given solid.…”

Section: Introductionmentioning

confidence: 99%

On the microscopic origin of the hysteresis loop in closed end pores – Adsorbate restructuring

Phadungbut

Nicholson

2016

Chemical Engineering Journal

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We present here compelling evidence for adsorbate restructuring as the microscopic origin of hysteresis in closed end pores. Our argument is based on molecular simulations in the grand canonical (GCE) and mesocanonical (MCE) ensembles, for argon adsorbed at 87K in slit mesopores of different topologies (open end, closed end and closed pores). The MCE isotherms have sigmoidal van der Waals type loops, while the GCE isotherms exhibit hysteresis loops, which are confined between the gas-like and liquid-like spinodal points. One interesting feature, not previously recognized, is that the condensation in the MCE isotherms for pores of different topologies is identical, and it occurs at the same chemical potential, which is the coexistence chemical potential of two phases in equilibrium: the liquid-like condensate and the gas-like phase. At the onset of the condensation, the liquid-like condensate is a thin liquid bridge formed by taking molecules from the metastable adsorbed film, resulting in a thinner and stable adsorbed film. As more molecules are added into the pore, the liquid bridge thickens along the axial direction and both menisci advance towards the pore mouth. As the menisci approach the pore mouth, the liquid condensate is progressively restructured to become more cohesive.When the pressure is reduced in the grand canonical ensemble (open system), a lower pressure is required to disrupt this cohesive structure, resulting in hysteresis in the closed end pores. The classical theories, which conclude that isotherms for closed end pores must be reversible, are in error because they assume that the interfacial energy parameter (the product of the surface tension and the liquid molar volume) has the same value as in a bulk liquid.

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“…The descending scanning curve is associated with stretching of the condensate in Region I, followed by evaporation, and the ascending scanning curve is associated with further layering of molecules on the pore walls in Region II, followed by condensation [15][16][17] .…”

Section: Introductionmentioning

confidence: 99%

Hysteresis and scanning curves in linear arrays of mesopores with two cavities and three necks

Zeng

Tan

et al. 2016

Colloids and Surfaces A: Physicochemical and Engineering Aspect

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Adsorption of argon at 87K in a linear array of slit mesopores composed of two cavities and three necks has been investigated using Grand Canonical Monte Carlo simulation. Hysteresis and scanning was found to depend on the relative size of the necks and cavities and on whether the necks are wider or narrower than the critical width that demarcates cavitation from pore blocking. There are 26 possible combinations for the linear array. By considering the behaviour of hysteresis scanning curves, we are able to identify four distinct groups: (i) Group 1: The descending scanning spans the boundary curve of the hysteresis loop due to stretching of the condensate in the small cavity.(ii) Group 2: The descending curve partially spans the loop and returns to the adsorption boundary. This occurs either because the condensate stretches in the small cavity, followed by evaporation via a pore blocking mechanism; or because the condensate evaporates as the meniscus recedes in the large neck that joins the two cavities.(iii) Group 3: The descending curve spans the loop as in Group 1 but there is a small sub-loop associated with emptying and filling of the large neck connecting the large cavity to the surrounding gas.

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Effects of temperature, pore dimensions and adsorbate on the transition from pore blocking to cavitation in an ink-bottle pore

Cited by 20 publications

References 35 publications

Scanning curves in wedge pore with the wide end closed: Effects of temperature

Scanning curves in wedge pore with the wide end closed: Effects of temperature

On the microscopic origin of the hysteresis loop in closed end pores – Adsorbate restructuring

Hysteresis and scanning curves in linear arrays of mesopores with two cavities and three necks

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