Grain Boundaries In Ice Research Articles

Crystalline clusters in mW water: Stability, growth, and grain boundaries.

With numerical simulations of the mW model of water, we investigate the energetic stability of crystalline clusters both for Ice I (cubic and hexagonal ice) and for the metastable Ice 0 phase as a function of the cluster size. Under a large variety of forming conditions, we find that the most stable cluster changes as a function of size: at small sizes, the Ice 0 phase produces the most stable clusters, while at large sizes, there is a crossover to Ice I clusters. We further investigate the growth of crystalline clusters with the seeding technique and study the growth patterns of different crystalline clusters. While energetically stable at small sizes, the growth of metastable phases (cubic and Ice 0) is hindered by the formation of coherent grain boundaries. A fivefold symmetric twin boundary for cubic ice, and a newly discovered coherent grain boundary in Ice 0, promotes cross nucleation of cubic ice. Our work reveals that different local structures can compete with the stable phase in mW water and that the low energy cost of particular grain boundaries might play an important role in polymorph selection.

How Do Intergranular Particles Affect the Flow of Ice?

Laboratory experiments that indicate rock particles can impede sliding along grain boundaries in ice may help researchers more accurately determine the composition of planetary ice masses.

Micro‐droplets containing sulfate in the Dome Fuji deep ice core, Antarctica: findings using micro‐Raman spectroscopy

Climatic signals in deep ice cores, particularly from ion concentrations, may be affected by the diffusion of liquid solution along grain boundaries of ice. Such solutions include sulfates. Because of the difficulty of detecting sulfate liquids in the ice matrix, we must infer the phase of the sulfates from the ice temperature and inclusion properties. In this study, we use micro‐Raman spectroscopy to determine the phase of three sulfate micro‐inclusions in the Dome Fuji ice core at 2798.5 m depth. Using a temperature‐ramp test, we find a peak position at 984 cm−1 and a change in the full width at half maximum of the SO stretching mode that identifies the sulfate in the micro‐droplets. Considering the peak position and full width at half maximum of sulfate inclusions, we argue that the sulfate would have existed as a micro‐droplet liquid on an air‐clathrate hydrate in the ice. Additionally, the increase in the low frequencies of the Raman spectrum below 30 cm−1 that we detect can be generally used to identify liquids in natural ice. Our investigation also indicates that the surface of air‐clathrate hydrates in ice is a preferred location for liquid micro‐inclusions. Copyright © 2016 John Wiley & Sons, Ltd.

Molecular dynamics simulations of tilt grain boundaries in ice

In this paper, molecular dynamics simulations (MDS) of symmetric tilt ice grain boundaries are presented. The MDS were carried out using the GROMACS v4.5.5 program, and the water molecules were described using the TIP5P-Ew model. The grain boundary energies, , relative to those of the surface free energies, , were obtained as a function of the misorientation angle Ψ, and compared with the values experimentally obtained. The results show a good correspondence between the experimental and simulated values. The planar density of coincidence sites at the grain boundary planes, Γ, was obtained as a function of ψ. The Γ values were compared with the simulated values and a relation between the minimum of the simulated values and the maximum of the Γ values was observed, suggesting that the CSL theory is a good starting point to detect low energy ice GBs.

Effect of temperature and potassium chloride impurity on the relative ⟨101̅0⟩ tilt grain boundary and surface free energies in ice.

The ratio of the grain boundary free energies relative to the surface free energies γgb/γs can be determined by measuring the root angles of the grooves formed at the intersection of the grain boundary with the free surface. The grooves were copied by plastic replicas, and the topographic details were revealed with a laser confocal 3D microscope. Values of γgb/γs were determined for high purity and potassium chloride doped ice bicrystals annealed at -5 and -18 °C. The studied samples were ⟨101̅0⟩/ψ tilt grain boundaries with ψ between 10 and 180°. The used KCl concentrations were 1 and 10 μmol/l, and the conductivity of the pure ice was 0.3 μS. ⟨101̅0⟩/60° grain boundary relative energies were also determined for different grain boundary inclinations. All the γgb/γs obtained values were analyzed and compared using the CSL (coincidence site lattice) theory. For pure samples annealed at -18 °C, an important variation of γgb/γs with the grain boundary inclination was found. In general, a remarkable correspondence between CSL planar density Γ and γgb/γs was observed. Results also showed that the increase of temperature and the impurity changes significantly γgb/γs.

Using Singlet Molecular Oxygen to Probe the Solute and Temperature Dependence of Liquid-Like Regions in/on Ice

Liquid-like regions (LLRs) are found at the surfaces and grain boundaries of ice and as inclusions within ice. These regions contain most of the solutes in ice and can be (photo)chemically active hotspots in natural snow and ice systems. If we assume all solutes partition into LLRs as a solution freezes, freezing-point depression predicts that the concentration of a solute in LLRs is higher than its concentration in the prefrozen (or melted) solution by the freeze-concentration factor (F). Here we use singlet molecular oxygen production to explore the effects of total solute concentration ([TS]) and temperature on experimentally determined values of F. For ice above its eutectic temperature, measured values of F agree well with freezing-point depression when [TS] is above ∼1 mmol/kg; at lower [TS] values, measurements of F are lower than predicted from freezing-point depression. For ice below its eutectic temperature, the influence of freezing-point depression on F is damped; the extreme case is with Na2SO4 as the solute, where F shows essentially no agreement with freezing-point depression. In contrast, for ice containing 3 mmol/kg NaCl, measured values of F agree well with freezing-point depression over a range of temperatures, including below the eutectic. Our experiments also reveal that the photon flux in LLRs increases in the presence of salts, which has implications for ice photochemistry in the lab and, perhaps, in the environment.

Hysteresis and return-point memory in colloidal artificial spin ice systems

Using computer simulations, we investigate hysteresis loops and return-point memory for artificial square and kagome spin ice systems by cycling an applied bias force and comparing microscopic effective spin configurations throughout the hysteresis cycle. Return-point memory loss is caused by motion of individual defects in kagome ice or of grain boundaries in square ice. In successive cycles, return-point memory is recovered rapidly in kagome ice. Memory is recovered more gradually in square ice due to the extended nature of the grain boundaries. Increasing the amount of quenched disorder increases the defect density but also enhances the return-point memory since the defects become trapped more easily.

H/D exchange kinetics in pure and HCl doped polycrystalline ice at temperatures near its melting point: Structure, chemical transport, and phase transitions at grain boundaries

We report the results of a fast thermal desorption spectroscopy study of the H/D isotopic exchange kinetics in a few micrometer thick, pure polycrystalline ice film and in ice films doped with HCl. Using the isotopic exchange reaction as a probe of transport processes in ice, we determined the effective H/D interdiffusion coefficients, D(eff), in pure and doped polycrystalline ice at temperatures ranging from -18 to -1 degree C. In the case of pure polycrystalline ice, D(eff) demonstrates an Arrhenius dependence on temperature with an effective activation energy of 69+/-3 kJ mol(-1) and a pre-exponential of 10(9+/-0.5) microm(2) ms(-1) up to -2 degrees C. According to our analysis, H/D interdiffusion coefficient at the grain boundaries also shows an Arrhenius dependence on temperature with an activation energy of 69+/-3 kJ mol(-1) and a pre-exponential of 10(11+/-1) microm(2) ms(-1). However, the addition of 0.04% of HCl results in a marked deviation of D(eff) from Arrhenius law at -8 degrees C, which is attributed to premelting at intersections of grain boundaries. We discuss the structure and transport properties of condensed aqueous phase at grain boundaries in polycrystalline ice at various temperatures.

Anisotropic elastocreep in glacial ice: A mechanism for intergranular melt and recrystallization

[1] Bonded ice crystals under pressure are in a heterogeneous stress state because of the mechanical anisotropy of constituent grains. This condition plays a role in intergranular melt and recrystallization, which in turn influence properties such as permeability and biologic habitability. To examine this, we develop an anisotropic elastocreep model simulating subgrain-scale stresses in polycrystalline ice, choosing in particular the thermal and deformational regime of the Lake Vostok accretion ice. A critical assumption with regard to localized melting is the macroscopic deviatoric stress. Our calculations indicate that for a macroscopic deviatoric stress of 50 kPa, ice at 0.04°C below the bulk melting temperature would contain regions, at scales ∼1% the grain size, where the liquid phase is thermodynamically favored. This translates to scales of ∼5 mm in the lower few meters of the Vostok accretion under a deviatoric stress that is plausible near the lake perimeter. Less internal melting is indicated in analyses of ice relatively far from the lake margins due to the assumed presence of lower macroscopic deviatoric stress. Simulated strain energy jumps of 1–2% across grain boundaries of accretion ice near the lake boundaries are large relative to free surface energy, indicating the importance of the former in boundary migration recrystallization. Collectively, these findings are consistent with measured dislocation densities (>107–1010 m−2) and irregular grain morphologies found in core samples. The calculated melting point depressions associated with anisotropy fall short of experimental values by a factor of ∼2, while the calculated strain rates deviate by ∼20%.

Microstructural evolution in sintered ice particles containing NaCl observed by low-temperature scanning electron microscope

Ice particles containing NaCl were made by spraying 0.043 M salt solution into liquid nitrogen. The ice particles were packed into capsules and annealed at -8 °C for 168 h and -25 °C for 20 h. This material can be considered as a model material for sintered snow containing impurities. The capsules were fractured open inside the low-temperature scanning electron microscope, which minimized the artefacts caused by cryofixation. The morphology of the sintered structure was observed with low-temperature scanning electron microscope. The microstructure of the sintered material consists of ice grains with a liquid meniscus containing NaCl between the grains. This structure is similar to the equilibrium morphology of water-filled veins in polycrystalline ice and liquid phase sintered metallic materials. The combined effect of the surface energies between the solid, liquid, and vapour governs the morphology of the microstructure. A dihedral angle where the brine intersects a grain boundary in ice of 8.0 ± 2.6°, and a contact angle for brine on ice at the interface with vapour of 5.0 ± 1.3° were measured, for samples quenched from -8 °C. Using the dihedral angle measurement, a surface energy value for ice-brine of 32.6 ± 0.1 mJ/m2 was calculated.

A Critical Review of the Low-Frequency Electrical Properties of Ice Sheets and Glaciers

I review current understanding of the low-frequency electrical properties of glaciers and ice sheets, and identify future research directions that challenge near-surface geophysicists and glaciologists. In cold ice electrical conduction occurs principally via [a] movement of protonic point defects in the lattice in low-impurity ice; [b] networks of impurities at grain boundaries in ice of moderate impurity content; and [c] triple junctions and grain boundaries in ice of high impurity content. I infer that in temperate ice Archie-type conduction is likely dominant. Arrhenius and Looyenga type models, respectively, describe well the increase in bulk resistivity with decreasing ice temperature and density. The activation energy in cold ice and firn is constant at [Formula: see text] but poorly constrained in temperate ice and snow. The bulk resistivity of cold ice ranges from [Formula: see text] at [Formula: see text] at [Formula: see text], and is much higher in temperate ice (up to [Formula: see text]). The effects of impurity characteristics, temperature, and density on complex conductivity are poorly understood, although selected real conductivity components apparently increase with frequency, impurity concentration, or temperature. Future research should exploit more rigorously low-frequency electrical techniques in the field and laboratory, and develop or adapt from other areas of electrical geophysics novel mathematical and statistical concepts for joint data inversion and integration, for glaciological purposes such as ice core logging and investigations of glacier dynamics, ice fracturing, and glacier hydrology. I conclude that low-frequency electrical techniques have unduly been neglected in glaciology as compared with higher-frequency radar techniques over the past few decades, suggesting opportunities for concerted research efforts into these techniques.

Interactions of organic molecules at grain boundaries in ice: A solvatochromic analysis

Empirical solvent polarity parameters were used to evaluate the nature and magnitude of the intermolecular interactions of eight dipolar organic solvatochromic indicators in aqueous solutions frozen at 253 or 77 K, using the concept that is generally employed to study the polarity of liquid solvents or solid surfaces. E T(30), E T(33), and E T N as well as α, acceptor number (AN) (hydrogen-bond donation ability), β (hydrogen-bond acceptor ability), and π * (polarity/polarizability) parameters were obtained by measuring the differences in the shifts of the absorption spectra of the probes. It was found that hydrogen-bond and electron-pair donating interactions were significant contributors to the polarity of a probe environment in ice and, at the same time, they were found to be substantially larger than those measured in liquid aqueous solutions and relatively insensitive to the sample temperature. While the former interaction type is attributed rather to the presence of water in a close vicinity of the probe molecules, the latter is evidently connected with the inter-probe interactions within the self-assembled molecular aggregations in conjunction with the water–probe interactions. The solvatochromic analysis revealed very weak dipole–dipole interactions ( π *) but the results are inconclusive. The data are consistent with a model according to which, upon freezing the aqueous solutions, the organic solute molecules are ejected to the grain boundaries to form highly concentrated liquid or frozen mixtures of organic and water molecules, having a high degree of complexity and exhibiting specific intermolecular interactions. Evaluation of the intermolecular polar interactions at the grain boundaries in ice should be of a great value in advancing our understanding of physical and chemical processes occurring in natural ice and snow.

Fuel movement along grain boundaries in ice

Abstract Knowledge about movement of hydrocarbon-based fuels in ice is relevant to marine and terrestrial fuel spills in polar regions, and to the dispersion of hydrocarbon-based drilling fluids used to maintain lithostatic pressure in deep ice coring projects. The latter is of concern from both environmental and sample integrity aspects, particularly for projects that plan to sample deep subglacial environments such as Lake Vostok. These concerns prompted us to examine the mobility of a liquid hydrocarbon fuel in non-fractured polycrystalline ice near the melting point in darkened conditions characteristic of deep glacial ice. Our experiments revealed rapid fuel propagation along intergranular tubes, at velocities up to 1.6 m h− 1, in ice with an overall impurity concentration ranging from 7 to 10 μM. This fuel movement, herein referred to as fuel tunneling, was absent in ice grown from distilled water with two- to three-fold fewer impurities, suggesting a role of dissolved contaminants which tend to concentrate along grain boundaries. Fuel tunneling commenced when ice temperatures were within 0.2 °C of melting and water vein diameters about 0.5 mm. Our results show that bubble free, non-fractured polycrystalline ice near its melting point is highly permeable to liquid hydrocarbon fuel via grain boundaries, a result that should be considered when sampling deep subglacial lakes, particularly those with overlying accretion ice.

Enhanced Protonation of Cresol Red in Acidic Aqueous Solutions Caused by Freezing

The protonation degree of cresol red (CR) in frozen aqueous solutions at 253 or 77 K, containing various acids (HF, HCl, HNO3, H2SO4, and p-toluenesulfonic acid), sodium hydroxide, NaCl, or NH4Cl, was examined using UV/Vis absorption spectroscopy. CR, a weak organic diacid, has been selected as a model system to study the acid-base interactions at the grain boundaries of ice. The multivariate curve resolution alternating least-squares method was used to determine the number and abundances of chemical species responsible for the overlaying absorption visible spectra measured. The results showed that the extent of CR protonation, enhanced in the solid state by 2-4 orders of magnitude in contrast to the liquid solution, is principally connected to an increase in the local concentration of acids. It was found that this enhancement was not very sensitive to either the freezing rate or the type of acid used and that CR apparently established an acid-base equilibrium prior to solidification. In addition, the presence of inorganic salts, such as NaCl or NH4Cl, is reported to cause a more efficient deprotonation of CR in the former case and an enhanced protonation in the latter case, being well explained by the theory of Bronshteyn and Chernov. CR thus served as an acid-base indicator at the grain boundaries of ice samples. Structural changes in the CR molecule induced by lowering the temperature and a presence of the constraining ice environment were studied by the absorption and 1H NMR spectroscopies. Cryospheric and atmospheric implications concerning the influence of acids and bases on composition and reactivity of ice or snow contaminants were examined.

The importance of pores in the electron stimulated production of D 2 and O 2 in low temperature ice

The effects of porosity and morphology of amorphous and crystalline D 2O ices on the electron stimulated generation and trapping of D 2 and O 2 have been studied by post-irradiation thermal desorption. The trapped product yields increase from crystalline ice to amorphous ice to highly porous amorphous ice, similar to observed ESD yields. This is attributed to the increased number of defects, traps and pores in amorphous ice. Molecular deuterium is released in the temperature range from 55 to 105 K for each of the samples, with two notable bursts at 115 and 132 K for porous amorphous ice. Low temperature release is associated with diffusion of D 2 through micropores in the ice matrix. Highly porous amorphous ice shows a striking spike in the release of D 2 at 80 K which has not previously been observed and must be a result of trapping of D 2 within enclosed macropores. The trapped D 2 in macropores may result from transport of excitation energy to the pore interface or from transport of D 2 through micropores at lower temperatures during TPD, or both. Molecular oxygen is retained within ice until much higher temperatures (>140 K). The release at this temperature is attributed to sintering and diffusion along grain boundaries in crystalline ice. The majority of trapped O 2 evolves with the desorption of the ice matrix, suggesting that clathrate hydrates may be important trapping sites. Amorphous ice releases a surge of trapped O 2 at the 160 K amorphous to crystalline phase transition, which is consistent with codeposition experiments. Highly porous ice exhibits much higher total yields of oxygen and shows a second strong spike in trapped O 2 release at 175 K.

Aggregation of Methylene Blue in Frozen Aqueous Solutions Studied by Absorption Spectroscopy

The paper presents a qualitative as well as quantitative spectroscopic study of methylene blue (MB) aggregation that occurs upon freezing the aqueous solutions over a wide concentration range. The Gaussian curve analysis and the multivariate curve resolution-alternating least squares method were used to determine the number and concentration of chemical species responsible for the overlaying absorption visible spectra measured. The results show the extent of aggregation for the concentrations above 10(-7) mol L(-1), being dependent on the freezing rate and the initial concentration. While the local concentration of MB at the grain boundaries of polycrystalline ice increased by approximately 3 orders of magnitude upon fast freezing at 77 K compared to the liquid phase, the concentration raised at least by 6 orders of magnitude upon slow freezing at 243 K. Since enhancement of the local concentration of solutes plays an important role in (photo)chemical transformations in solid aqueous media, this work helps to understand how the initial conditions control the course of the process. The results are relevant in other interdisciplinary fields, such as environmental chemistry, cosmochemistry, or geochemistry.

Dynamic observations of dislocation/grain-boundary interactions in ice

AbstractDislocation/grain-boundary (GB) interactions have been studied in situ in polycrystalline ice using synchrotron X-ray topography in the temperature range 0° to –15°C GBs were observed to act both as sources of lattice dislocations and as strong obstacles to dislocation motion. Dislocations were observed to form pile-ups at GBs upon loading. Generally the basal slip system with the highest Schmid factor was found to be the most active, and dislocations were emitted from GB facets as semi-hexagonal loops in order to relieve the stress build-up from GB sliding. When the relative orientation of two adjacent grains and the orientation of the GB between them with respect to the loading direction discouraged GB sliding, thus suppressing dislocation nucleation at the GB, dislocations originating in one grain piled up at the GB and led to slip transmission through the GB The latter geometrical arrangement is rarely encountered, suggesting that slip transmission through grain boundaries in ice is a rare event. When basal slip was suppressed, i.e. when the loading direction lay in the basal plane, slip occurred by the glide of a fast edge segment on non-basal planes.

Observation of slip transmission through a grain boundary in ice

In-situ X-ray topography has been used to provide the first clear demonstration of slip transmission through a grain boundary in hexagonal ice. Although the ice was deformed under creep conditions, the relative orientation of the grains and the orientation of the grain boundary with respect to the loading direction discouraged grain boundary sliding and, thus, suppressed dislocation nucleation at the grain boundary. This particular geometrical arrangement is rarely encountered, suggesting that slip transmission through grain boundaries in ice is a rare event.

Anelasticity and grain boundary relaxation of ice at high temperatures

The anelastic behaviour of polycrystalline hexagonal ice has been studied over the temperature range 210-273 K, frequency range 0.5 to 40 Hz in a three-point bending mode. The crystal size was varied by slow and rapid crystallization and the effect of ageing on the anelastic behaviour of the variously prepared ice samples was studied. The relaxation peak observed at 250 K for a frequency of 1 Hz is attributed to the grain boundary motion and discussed in terms of various models. Changes in the microstructure on ageing of ice increase the strength of the grain boundary relaxation, and alter the loss attributed to dislocation movement and creep deformation. The grain boundary relaxation occurs with a single relaxation time with an activation energy of 54.3 kJ per mole which is more than twice the activation energy for viscous flow of water at 273 K. This suggests that the relaxation associated with the sliding of grain boundaries in polycrystalline ice occurs by distortion of H-bonds between the tetrahedrally bonded water molecules, leading to the breaking of at least two intermolecular H-bonds in the local regions of the grain boundaries.

Dynamic observations of dislocation generation at grain boundaries in ice

Dynamic in situ X-ray topographic deformation studies have been performed on polycrystalline ice. Based on these observations, a new and dominant mechanism for dislocation nucleation, which is related to stress concentrations observed in the vicinity of grain boundaries, is proposed. It was found that the areas near grain boundaries always deform before the grain interiors. Lattice dislocations were nucleated continuously at large-angle grain boundaries, driven by internal stresses that are higher than the external stress. The dislocations, once generated, glide on the basal plane as semi-hexagonal loops. The shape of these loops is a result of a balance of the stresses present. The dislocation generation mechanism at grain boundaries was found to depend strongly on the basal plane orientation relative to both the loading direction and the grain boundary plane.