Anomalous diffusion of water molecules at grain boundaries in ice I<sub>h</sub>

Moreira, P.A.F.P.; Veiga, Rga; Ribeiro, Ingrid de Almeida; Freitas, Rodrigo; Helfferich, Julian; Koning, Maurice de

doi:10.1039/c8cp00933c

Cited by 20 publications

(21 citation statements)

References 48 publications

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“…If we assume that the hydrate film or thicker crust consists of cubic crystals with edges of 10 μm long, then the hydraulic radius of the conduits is estimated to be 2.7 nm (see supporting information for details). This conduit size is in general agreement with other works (Moreira et al, ; Wu et al, ). Similar water migration also occurs through ice‐grain boundaries during hydrate formation from ice particles (Henning et al, ; Wang et al, ).…”

Section: Discussion and Summarysupporting

confidence: 93%

Methane Hydrate Film Thickening in Porous Media

Lei

Seol

Myshakin

2019

Geophysical Research Letters

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Methane hydrate formation accompanied by upward migration of methane in sediments was studied. Methane hydrate film forms initially along the interface between the gas and surrounding pore fluid when methane reaches the hydrate stability zone. Subsequent film thickening and related mass transfer are critical but have not been studied previously. Experimental and theoretical studies were performed to investigate the film thickening and rate-limiting mechanisms. Initial gas density affects the stability of the growing hydrate film, and mass transfer through hydrate film is proposed as a rate-limiting step for hydrate growth.Plain Language Summary Gas hydrate films can quickly form when gas and water meet each other given proper pressure and temperature. Yet, little is known about what occurs afterward. We use both experimental and theoretical approaches to investigate slow transformation of methane bubbles to methane hydrate. Two experiments were conducted using gas densities lower or higher than methane density in methane hydrate. In the lower-density case, the initially formed hydrate film breaks, which lets water invade into the gas bubble. By contrast, the hydrate film maintains its integrity in the higher-density case, and the slowly formed hydrate takes over both the spaces initially occupied by gas and water. Observations indicate that both water transfer into the gas bubble and outward gas transfer from the bubble occur through hydrate films. A theoretical analysis explores these processes based on the slow mass migration via seemingly solid hydrate: (1) gas diffusion driven by gas concentration gradient in hydrate and (2) water flow via conduits within polycrystalline hydrate driven by pressure gradients. The mass transfer rates match experimental observations and agree with previous studies. Results suggest that natural hydrate formed from free gas at significant depth could have residual gas inclusions for millions of years.

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Section: Discussion and Summarysupporting

confidence: 93%

Methane Hydrate Film Thickening in Porous Media

Lei

Seol

Myshakin

2019

Geophysical Research Letters

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“…Consequently, the trend of permeability ( P = S × D ) would be different from that of diffusivity established in this study (Figure c): P / P 0 ≈ exp[−( E D + E S )/ k B T ]. ,, For example, field experiments have suggested P (He) > P (Ne) > P (O 2 ) > P (Ar) > P (Kr) ≈ P (Xe) ≈ P (CO 2 ) ≈ P (N 2 ) based on the firn–air composition in the bubble close-off zone of polar glaciers. , Further studies are necessary with well-designed atomistic level simulations for such molecular gases to precisely understand the gas permeation process, particularly gas adsorption on the ice-Ih surface, penetration into the ice-Ih lattice structure, and thermodynamics stability changes. ,,, Additionally, considerations should be made on the crystallinity and structural defects in the ice layer surrounding closed-off bubbles. The grain boundaries in polycrystalline ice and the potential presence of the amorphous layer at the gas–ice interface would have an effect on both dissolution and molecular diffusion processes. , The structural and ionic defects in ice-Ih, such as molecular disorientations, ionic defects, and molecular vacancies, might hinder diffusion dynamics (see refs , and and other references therein).…”

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confidence: 99%

Molecular Mechanism of Gas Diffusion in Ice-Ih

Han

Lee

et al. 2021

ACS Earth Space Chem.

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Atmospheric gases trapped in polar ice have been used to reconstruct polar and global climate changes, providing better time resolution when less diffused. Experiments have shown that gas diffusion in ice is negligible on a laboratory time scale, but its cumulative impact on old glacial ice (>1M yr) remains unclear. Here, we employ density functional theory calculations to investigate the diffusion mechanism of gases trapped in ice-Ih from the atomistic level. The results suggest that the diffusion energy barrier between interstitial sites is primarily dependent on the atomic size and charge distribution of hopping gases. The diffusion of noble gases (He, Ne, Ar, Kr, and Xe) primarily occurs via the interstitial mechanism, consistent with previous results of classical molecular dynamics simulations. In contrast, the precisely determined diffusion paths and energy barriers for CO 2 , O 2 , and N 2 suggest that these molecular gases prefer to hop along the hexagonal channel also via the interstitial mechanism, and the bond-breaking mechanism proposed previously to explain the diffusion of those molecular gases as fast as Ne may be unnecessary.

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“…In the meantime, advances in the modeling and simulation of ice GB pre-melting remain scarce. 23,24 The present study is also motivated by a recent highresolution electron microscopy study by Algara-Siller et al 25 In their study, the two dimensional (2D) GBs between the crystallites of monolayer ice which adopts unexpected simple square lattice, inside the hydrophobic bi-graphene nano-capillaries, were directly observed. Although no sign of GB melting was found within specific setup in the experiments, their observations still provide a compelling brand-new perspective for the exploration of GB premelting of ices.…”

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confidence: 83%

“…The transport result is in contrast to premelting at GBs in 3D ice I h , in which transport of the water molecules within the premelting layer was predicted to behave sub-diffusively even at a temperature just below the T m . 24 To examine the validity of Eq. 1 for the 2D GB premelting transition in monolayer ice in the nano-channels, we plot the calculated time-averaged width of the premelting band, w, as a function of the undercooling, ∆T = T m − T on a linear-log plot in Fig.…”

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confidence: 99%

Grain boundary premelting of monolayer ices in 2D nano-channels

Liang

et al. 2019

Molecular Physics

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We employ molecular-dynamics (MD) simulations to study grain boundary (GB) premelting in ices confined in two-dimensional hydrophobic nano-channels. Premelting transitions are observed in symmetric tilt GBs in monolayer ices and involve the formation of a premelting band of liquid phase water with a width that grows logarithmically as the melting temperature is approached from below, consistent with the existing theory of GB premelting. The premelted GB is found rough for a broad range of temperature below the melting temperature, the two ice-premelt interfaces bounding the melted GB are engaged with long wave-length parallel coupled fluctuations. Based on current MD simulation study, one may expect GB premelting transitions exist over a wide range of low dimensional phases of confined ice and shows important consequences for crystal growth of low dimensional ices.The term premelting refers to the formation of a thermodynamically stable liquid film at solid interfaces at temperatures below but close to the bulk melting temperature T m . 1 The premelting transitions occur in all types of solids, they stand out in the case of ice, because of their association with terrestrial life and the importance of their environmental effects. 2 Studies of premelting at ice surfaces have been carried out with a wide variety of modern experimental and molecular-level modeling techniques (see in Ref.[2 and 3] and references therein), these studies have demonstrated the rich nature and complexity of the ice surface premelting behaviors, which covers a span from quasi-liquid bilayer-by-bilayer melting process 4,5 to complete, 6 incomplete premelting 7 and a first-order phase transition between two distinct premelting states, 8 depending on temperature, surface crystallographic orientation and even atmospheric environment.In comparison to surface premelting, the complexity mentioned above is only the beginning to be explored for grain boundary (GB) premelting of ices, as more bicrystallography parameters (symmetry, misorientation, and boundary plane) are introduced. It is well known that GB premelting of ice may play a vital role in a variety of processes of geophysical, geological and atmospheric interest. 2 However, the challenges inherent in characterizing the structure of "buried" internal GBs have significantly limited the number of direct experimental studies, 9 and have resulted in a situation that GB premelting is one of most important yet the least studied aspects of ice. During the last decade, GB premelting of pure metals and binary alloys, have been the subject of continuum modeling studies 10-15 and atomistic simulations studies, 16-22 which led to insights into the nature of the thermodynamic driving forces of the GB premelting as a function of GB bicrystallography. In the meantime, advances in the modeling and simulation of ice GB pre-melting remain scarce. 23,24 The present study is also motivated by a recent highresolution electron microscopy study by In their study, the two dimensional (2D) GBs between the crystal...

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Anomalous diffusion of water molecules at grain boundaries in ice I_h

Cited by 20 publications

References 48 publications

Methane Hydrate Film Thickening in Porous Media

Methane Hydrate Film Thickening in Porous Media

Molecular Mechanism of Gas Diffusion in Ice-Ih

Grain boundary premelting of monolayer ices in 2D nano-channels

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Anomalous diffusion of water molecules at grain boundaries in ice Ih

Cited by 20 publications

References 48 publications

Methane Hydrate Film Thickening in Porous Media

Methane Hydrate Film Thickening in Porous Media

Molecular Mechanism of Gas Diffusion in Ice-Ih

Grain boundary premelting of monolayer ices in 2D nano-channels

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Anomalous diffusion of water molecules at grain boundaries in ice I_h