Hysteresis at the gas-liquid and liquid-solid phase transitions of capillary confined CO<sub>2</sub>: a positronium annihilation study

Duffy, J. A.; Wilkinson, N.J.; Fretwell, H. M.; Alam, M. A.

doi:10.1088/0953-8984/7/3/003

Cited by 30 publications

(36 citation statements)

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“…there is large and important group of restricted geometry objects, namely materials confined within porous media (hereinafter we will call them confined materials -CM). In recent years properties of CM and in particular various types of phase transitions (PT) (superconducting [1,2], superfluid [3,4], melting-freezing [5,6,7,8,9,10,11] and others PTs [12,13,14,15,16,17,18,19,20,21,22] in different CM have been extensively studied by different experimental methods including calorimetry [5,7,20], NMR [9,21], ultrasonic [8,9] and dielectric [12,14,15] measurements, Raman [10,13], X-ray [12,16,17,18] and neutron scattering [10,14,22,23,24,25,26], differential thermal analysis [19] etc. It has been shown that CM can form either a system of isolated particle...…”

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confidence: 99%

Temperature Evolution of Sodium Nitrite Structure in a Restricted Geometry

et al. 2002

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The NaNO2 nanocomposite ferroelectric material in porous glass was studied by neutron diffraction. For the first time the details of the crystal structure including positions and anisotropic thermal parameters were determined for the solid material, embedded in a porous matrix, in ferroand paraelectric phases. It is demonstrated that in the ferroelectric phase the structure is consistent with bulk data but above transition temperature the giant growth of amplitudes of thermal vibrations is observed, resulting in the formation of a "premelted state". Such a conclusion is in a good agreement with the results of dielectric measurements published earlier.

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Section: Introductionmentioning

confidence: 99%

Temperature Evolution of Sodium Nitrite Structure in a Restricted Geometry

et al. 2002

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“…It has long been known that confinement can affect the thermodynamic behavior of imbibed liquids, such as suppressing the liquid-solid transition and introducing hysteresis between freezing and melting [4,5]. More recently, attention has focused on the microscopic structure of the adsorbed phases where confinement can not only change the microscopic structure, but also eliminate or introduce new transitions or stabilize new phases.…”

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Mobility Transition of Solid Rare Gases in Confined Environments

Sokol²,

Sn³

2002

Phys. Rev. Lett.

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We report the results of x-ray diffraction and small angle scattering studies of Ar and Kr confined in sol-gel and Vycor glasses. The confined liquid crystallizes in a disordered hcp structure on freezing. Upon further cooling a sharp transition occurs at a reduced temperature of T/T(m) approximately 0.65, where the crystalline structure disappears and the total scattering decreases. This behavior marks the onset of a well-defined mobility transition, where the confined sample migrates out of the pore space.

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“…For example, in classical systems the liquid-gas transition is enhanced with respect to the bulk [1,2] while the liquid-solid transition is suppressed [2,3]. Hysteresis, which appears to be a stable thermodynamic behavior, is also introduced into these transitions.…”

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New Disorder Induced Phase Transitions of Classical Rare Gases in Porous Vycor Glass

1998

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We report the results of x-ray diffraction studies of Ar and Kr confined in Vycor glass. The freezing and melting temperatures of both Ar and Kr were suppressed well below their bulk freezing points. On solidification, both samples crystallized in a disordered hexagonal close packed structure similar to that observed in molecular dynamics simulations of confined solids. A new solid-solid phase transition is observed at a reduced temperature of T ͞T f ഠ 0.5 when confined to Vycor. Below this temperature the disordered hexagonal closed packed structure coexists with the fcc structure.[S0031-9007 (98)06675-7] PACS numbers: 61.43.Gt, 61.10.NzThe effects of finite size and confinement on gases, liquids, and solids adsorbed in mesoporous materials, such as porous glasses and zeolites, is a topic of current interest for classical and quantum systems. For example, in classical systems the liquid-gas transition is enhanced with respect to the bulk [1,2] while the liquid-solid transition is suppressed [2,3]. Hysteresis, which appears to be a stable thermodynamic behavior, is also introduced into these transitions. Quantum transitions show equally dramatic behavior. For example, the superfluid transition of 4 He in Vycor is substantially suppressed while the critical exponents remain unchanged. However, confinement in aerogel results in only a small suppression but substantially different critical exponents [4,5]. 3 He, on the other hand, has superfluid phases in high porosity aerogels [6,7], but not in lower porosity confining geometries.Microscopic structural studies of materials confined to mesoporous media have only recently been undertaken, and a variety of different behaviors have been reported. In some cases, such as Hg in Vycor [8], the structure of the confined solid is identical to that of the bulk while in other cases, such as H 2 O and D 2 in Vycor [9,10], confinement stabilizes new structures not present in the bulk. Confinement can also suppress crystalline order, such as O 2 in xerogel [11], resulting in a glassy solid phase. Confinement has not, however, been observed to introduce new phase transitions in any systems that have been studied to date.In this Letter, we report x-ray diffraction studies of Ar and Kr adsorbed in Vycor. As in many other systems, a suppression of the liquid-solid transition hysteresis between freezing and melting is observed. On freezing, both Ar and Kr are observed to form a disordered hexagonal close packed (dhcp) structure, characterized by random plane stacking, in contrast to the bulk fcc structure. A new phase transition, which is absent from the bulk phase diagram, occurs at roughly half of the freezing temperature below which both Kr and Ar exhibit coexistence of the dhcp and fcc phases. This solid-solid structural phase transition is repeatable on cycling and no appreciable hysteresis is observed. Thus, the coexistence phase appears to be a true disorder-induced thermodynamic phase, rather than a metastable phase.The confining media used in these studies was Vycor glass. Vy...

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Hysteresis at the gas-liquid and liquid-solid phase transitions of capillary confined CO₂: a positronium annihilation study

Cited by 30 publications

References 11 publications

Temperature Evolution of Sodium Nitrite Structure in a Restricted Geometry

Temperature Evolution of Sodium Nitrite Structure in a Restricted Geometry

Mobility Transition of Solid Rare Gases in Confined Environments

New Disorder Induced Phase Transitions of Classical Rare Gases in Porous Vycor Glass

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Hysteresis at the gas-liquid and liquid-solid phase transitions of capillary confined CO2: a positronium annihilation study

Cited by 30 publications

References 11 publications

Temperature Evolution of Sodium Nitrite Structure in a Restricted Geometry

Temperature Evolution of Sodium Nitrite Structure in a Restricted Geometry

Mobility Transition of Solid Rare Gases in Confined Environments

New Disorder Induced Phase Transitions of Classical Rare Gases in Porous Vycor Glass

Contact Info

Product

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Hysteresis at the gas-liquid and liquid-solid phase transitions of capillary confined CO₂: a positronium annihilation study