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

2009 ◽  
Vol 130 (5) ◽  
pp. 054501 ◽  
Author(s):  
Haiping Lu ◽  
Stephanie A. McCartney ◽  
Vlad Sadtchenko
Keyword(s):  
Phase Transitions ◽  
Melting Point ◽  
Grain Boundaries ◽  
Chemical Transport ◽  
Polycrystalline Ice ◽  
Exchange Kinetics

scholarly journals The Effect of Non-Hydrostatic Stress on Intergranular Water Veins and Lenses in Ice

1972 ◽  
Vol 11 (61) ◽  
pp. 81-101 ◽  
Author(s):  
J. F. Nye ◽  
S. Mae
Keyword(s):  
Melting Point ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Hydrostatic Stress ◽  
Pure Shear ◽  
Triple Junctions ◽  
Polycrystalline Ice ◽  
Glacier Ice ◽  
Set Up ◽  
Ice Water

AbstractPolycrystalline ice at the melting point has been observed in the laboratory to contain veins of water at the places where three grains meet. Under uniaxial compression lenticular water inclusions appeared at grain boundaries perpendicular to the stress, while the nearby vein began to freeze. A similar effect occurred in tension on grain boundaries parallel to the stress. When the stress on the plane of the boundary was a pure shear stress, no effect was observed. The water lenses produced by stress increased in size and decreased in number after the stress was removed. The effect under compression is explained quantitatively by the combined effects of curvature and pressure on the melting point of an ice–water interface. The rate of formation of the lenses and of their coarsening is greatly reduced by the internal pressures set up in the lenses as a result of expansion on freezing and contraction on melting; transient creep to accommodate volume changes is an essential part of the process. The effect in a grain boundary under tension may arise from pressure caused by sliding on other grain boundaries; it was absent in a bicrystal.It is concluded that internal melting and freezing at grain boundaries and veins will occur in temperate glacier ice, with some effect, not discussed here, on its permeability to water. Any pure solid at its melting point which has a dihedral angle for the liquid phase in contact with a grain boundary between 0° and 60° should show similar behaviour, in that non-hydrostatic stress should cause liquid to move away from triple junctions between grains and into grain boundaries. There may be implications for the Frank theory of the upwelling of melt fluid in the Earth’s upper mantle.

scholarly journals The Effect of Non-Hydrostatic Stress on Intergranular Water Veins and Lenses in Ice

1972 ◽  
Vol 11 (61) ◽  
pp. 81-101 ◽  
Author(s):  
J. F. Nye ◽  
S. Mae
Keyword(s):  
Melting Point ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Hydrostatic Stress ◽  
Pure Shear ◽  
Triple Junctions ◽  
Polycrystalline Ice ◽  
Glacier Ice ◽  
Set Up ◽  
Ice Water

AbstractPolycrystalline ice at the melting point has been observed in the laboratory to contain veins of water at the places where three grains meet. Under uniaxial compression lenticular water inclusions appeared at grain boundaries perpendicular to the stress, while the nearby vein began to freeze. A similar effect occurred in tension on grain boundaries parallel to the stress. When the stress on the plane of the boundary was a pure shear stress, no effect was observed. The water lenses produced by stress increased in size and decreased in number after the stress was removed. The effect under compression is explained quantitatively by the combined effects of curvature and pressure on the melting point of an ice–water interface. The rate of formation of the lenses and of their coarsening is greatly reduced by the internal pressures set up in the lenses as a result of expansion on freezing and contraction on melting; transient creep to accommodate volume changes is an essential part of the process. The effect in a grain boundary under tension may arise from pressure caused by sliding on other grain boundaries; it was absent in a bicrystal.It is concluded that internal melting and freezing at grain boundaries and veins will occur in temperate glacier ice, with some effect, not discussed here, on its permeability to water. Any pure solid at its melting point which has a dihedral angle for the liquid phase in contact with a grain boundary between 0° and 60° should show similar behaviour, in that non-hydrostatic stress should cause liquid to move away from triple junctions between grains and into grain boundaries. There may be implications for the Frank theory of the upwelling of melt fluid in the Earth’s upper mantle.

MICROSTRUCTURAL EVOLUTION OF Al-Cu-Mg-Ag ALLOY WITH TRACE Zr ADDITION DURING TWO-STEP HOMOGENIZATION

2009 ◽  
Vol 23 (06n07) ◽  
pp. 855-862 ◽  
Author(s):  
FEIYUE MA ◽  
ZHIYI LIU
Keyword(s):  
Melting Point ◽  
Grain Boundaries ◽  
Microstructural Evolution ◽  
Cast Alloy ◽  
Scanning Calorimetry ◽  
Zr Addition ◽  
Homogenization Time ◽  
The Matrix ◽  
Higher Temperature ◽  
Lower Temperature

The microstructural evolution in an Al - Cu - Mg - Ag alloy with trace Zr addition during homogenization treatment was characterized by Differential Scanning Calorimetry (DSC), Scanning Electron Microscopy (SEM) and Energy-dispersive X-ray Spectroscopy (EDS). It was shown that the low-melting-point phase segregating toward grain boundaries is Al 2 Cu , with a melting point of 523.52°C. A two-step homogenization process was employed to optimize the microstructure of the as-cast alloy, during which the alloy was first homogenized at a lower temperature, then at a higher temperature. After homogenized at 420°C for 6 h, Al 3 Zr particles were finely formed in the matrix. After that, when the alloy was homogenized at an elevated temperature for a longer time, i.e., 515°C for 24 h, most of the precipates at the grain boundaries were removed. Furthermore, the dispersive Al 3 Zr precipitates were retained, without coarsening greatly in the final homogenization step. A kinetics model is employed to predict the optimal homogenization time at a given temperature theoretically, and it confirms the result in present study, which is 420°C/6h+515°C/24h.

Effect of grain boundaries in La0.84Sr0.16CoO3−δ on oxygen diffusivity and surface exchange kinetics

2021 ◽  
Author(s):  
Natalia Porotnikova ◽  
Andrei Farlenkov ◽  
Sergey Naumov ◽  
Maxim Vlasov ◽  
Anna Khodimchuk ◽  
...  
Keyword(s):  
Single Crystal ◽  
Grain Boundaries ◽  
Gas Phase ◽  
Oxygen Exchange ◽  
Polycrystalline Specimen ◽  
Surface Exchange ◽  
Oxygen Diffusivity ◽  
Exchange Kinetics ◽  
Oriented Single Crystal

The 16O/18O oxygen exchange kinetics between the gas phase and the oriented single crystal and polycrystalline specimen has been studied; the rates of individual stages of oxygen exchange have been calculated and discussed.

scholarly journals Increasing contribution of grain boundary compliance to polycrystalline ice elasticity as temperature increases

2018 ◽  
Vol 64 (246) ◽  
pp. 669-674
Author(s):  
COLIN M. SAYERS
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Orientation Distribution ◽  
Resonant Ultrasound Spectroscopy ◽  
Wave Velocities ◽  
Polycrystalline Ice ◽  
Resonant Ultrasound ◽  
Increasing Temperature ◽  
Shear Compliance

ABSTRACTMeasured elastic stiffnesses of ice polycrystals decrease with increasing temperature due to a decrease in grain boundary stiffness with increasing temperature. In this paper, we represent grain boundaries as imperfectly bonded interfaces, across which traction is continuous, but displacement may be discontinuous. We express the additional compliance due to grain boundaries in terms of a second-rank and a fourth-rank tensor, which quantify the effect on elastic wave velocities of the orientation distribution as well as the normal and shear compliances of the grain boundaries. Measurement of the elastic stiffnesses allows determination of the components of these tensors. Application of the method to resonant ultrasound spectroscopy measurements made on ice polycrystals enables determination of the ratio BN/BS of the normal to shear compliance of the grain boundaries, which are found to be more compliant in shear than in compression. The ratio BN/BS is small at low temperatures, but increases as temperature increases, implying that the normal compliance increases relative to the shear compliance as temperature increases.

scholarly journals Phase Polymorphism of [Co(DMSO)6](BF4)2 Studied by Differential Scanning Calorimetry

2006 ◽  
Vol 61 (3-4) ◽  
pp. 180-188 ◽  
Author(s):  
Anna Migdał-Mikuli ◽  
Łukasz Skoczylas ◽  
Elżbieta Szostak
Keyword(s):  
Differential Scanning Calorimetry ◽  
Phase Transitions ◽  
Melting Point ◽  
Title Compound ◽  
Metastable Phases ◽  
Scanning Calorimetry ◽  
Phase Polymorphism ◽  
Solid Phases ◽  
High Degree ◽  
Dynamical Disorder

Five solid phases of [Co(DMSO)6](BF4)2 have been detected by differential scanning calorimetry (DSC). Phase transitions were detected between the following solid phases: stable KIb↔ stable KIa at T̅C4 = (328±2) K, metastable KIII ↔ undercooled phase K0 at T̅C3 = (383±4) K, metastable KII ↔ undercooled K0 at T̅C2 = (399±2) K and stable KIa ↔ stable K0 at T̅C1 = (404±1) K. The title compound melts at Tm = 440 K. From the entropy changes at the melting point and at phase transitions it can be concluded that the phases K0 and undercooled K0 are orientationally dynamically disordered crystals. The stable phases KIa, KIb are ordered solid phases. The metastable phases KII and KIII are probably solid phases with a high degree of orientational dynamical disorder

scholarly journals Recrystallization processes, microstructure and crystallographic preferred orientation evolution in polycrystalline ice during high-temperature simple shear

2019 ◽  
Vol 13 (5) ◽  
pp. 1495-1511 ◽  
Author(s):  
Baptiste Journaux ◽  
Thomas Chauve ◽  
Maurine Montagnat ◽  
Andrea Tommasi ◽  
Fabrice Barou ◽  
...  
Keyword(s):  
High Temperature ◽  
Grain Boundary ◽  
Dynamic Recrystallization ◽  
Grain Boundaries ◽  
Simple Shear ◽  
Shear Plane ◽  
Preferred Orientation ◽  
Dislocation Slip ◽  
Crystallographic Preferred Orientation ◽  
Polycrystalline Ice

Abstract. Torsion experiments were performed in polycrystalline ice at high temperature (0.97 Tm) to reproduce the simple shear kinematics that are believed to dominate in ice streams and at the base of fast-flowing glaciers. As clearly documented more than 30 years ago, under simple shear ice develops a two-maxima c axis crystallographic preferred orientation (CPO), which evolves rapidly into a single cluster CPO with a c axis perpendicular to the shear plane. Dynamic recrystallization mechanisms that occur in both laboratory conditions and naturally deformed ice are likely candidates to explain the observed CPO evolution. In this study, we use electron backscatter diffraction (EBSD) and automatic ice texture analyzer (AITA) to characterize the mechanisms accommodating deformation, the stress and strain heterogeneities that form under torsion of an initially isotropic polycrystalline ice sample at high temperature, and the role of dynamic recrystallization in accommodating these heterogeneities. These analyses highlight an interlocking microstructure, which results from heterogeneity-driven serrated grain boundary migration, and sub-grain boundaries composed of dislocations with a [c]-component Burgers vector, indicating that strong local stress heterogeneity develops, in particular, close to grain boundaries, even at high temperature and high finite shear strain. Based on these observations, we propose that nucleation by bulging, assisted by sub-grain boundary formation and followed by grain growth, is a very likely candidate to explain the progressive disappearance of the c axis CPO cluster at low angle to the shear plane and the stability of the one normal to it. We therefore strongly support the development of new polycrystal plasticity models limiting dislocation slip on non-basal slip systems and allowing for efficient accommodation of strain incompatibilities by an association of bulging and formation of sub-grain boundaries with a significant [c] component.

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