Creep relaxation around a crack tip in an ice crystal

Crystal Growth & Design

2002

Three techniques have been used to study dislocations in ice: etch pitting-replication, transmission electron microscopy, and X-ray topography (XT). Each is considered, and it is shown that the most useful is XT. This is because ice has low absorption of X-rays and can be produced with a low dislocation density, thus, allowing relatively thick specimens to be studied. The many useful observations that have been made with conventional XT are presented. However, the introduction of high-intensity synchrotron radiation showed that conventional XT observations are of dislocations that have undergone recovery. Thus, the important dynamic observations and measurements that have been made using synchrotron XT are also outlined. In single crystals, it has been shown that slip mainly occurs by the movement of screw and 60° a/3〈112̄0〉 dislocations on the basal plane. In addition, the operation of Frank-Read sources has been clearly demonstrated, and dislocation velocities have been measured. In contrast, in polycrystals, dislocation generation has been observed to occur at stress concentrations at grain boundaries, and this completely overwhelms any lattice dislocation generation mechanisms. The nature of faulted dislocation loops has been determined in both polycrystals and single crystals.

Section: Etch Pittingmentioning

confidence: 99%

Examination of Dislocations in Ice

Crystal Growth & Design

2002

“…ETCH PITTING/REPLICATION Since the first observations that etch pits in ice correspond with dislocations, etch pitting studies have shown that dislocations play a role in its plastic flow (Krausz and Gold, 1967;Kuroiwa, 1969;Levi et al, 1965;Muguruma, 1961;Sinha, 1977Sinha, , 1978Wei and Dempsey, 1994). The technique involves coating the surface of ice with a formvar solution, which produces an etch pit where a dislocation intersects the surface and forms a replica of the pit (see Fig.…”

Section: ϫ4mentioning

confidence: 97%

“…For example, features around a deformed notch where no etch-pits are present have been interpreted as being either dislocation free zones or as having a very high dislocation density (Wei and Dempsey, 1994)! Also, etch pitting-replication studies pur- portedly showing dislocation pile-ups against grain boundaries (Sinha, 1978) may have actually revealed emission of dislocations from the grain boundaries.…”

Section: ϫ4mentioning

confidence: 99%

Imaging dislocations in ice

Microscopy Res & Technique

2003

Three techniques have been used to study dislocations in ice: etch pitting-replication, transmission electron microscopy, and X-ray topography (XT). It is shown that, because ice is a weak absorber of X-rays and can be produced with a low dislocation density, allowing relatively thick specimens to be studied, the most useful technique is XT. The observations that have been made with conventional XT are briefly outlined. However, the introduction of high-intensity synchrotron radiation, with its concomitant short exposure times, showed that images obtained through conventional XT observations were of dislocations that had undergone recovery. The important dynamic observations and measurements that have been made using synchrotron X-ray topography are presented. Dynamic synchrotron X-ray topography observations of ice single crystals undergoing deformation in situ have shown that slip mainly occurs by the movement of screw and 60 degrees (1/3) [1120] dislocations on the basal plane, although non-basal slip by edge dislocations can also occur. The operation of Frank-Read and other dislocation multiplication sources have been clearly demonstrated and dislocation velocities have been measured. In contrast, in polycrystals, dislocation generation occurred at grain boundaries where there are stress concentrations before lattice dislocation generation mechanisms operate. Faulted dislocation loops have been determined to be mainly interstitial in both polycrystals and single crystals.

“…Etch-pitting was the first technique used to examine dislocations in ice [90][91][92][93][94][95]. Typically, the surface of the ice is coated with formvar and an etch pit forms where a dislocation intersects the surface.…”

Section: Dislocationsmentioning

confidence: 99%

Microstructural characterization of snow, firn and ice

Phil. Trans. R. Soc. A.

2019

This paper provides an overview of techniques used to characterize the microstructure of snow, firn and ice. These range from traditional optical microscopy techniques such as examining thin sections between crossed polarizers to various electron-optical and X-ray techniques. Techniques that could have an impact on microstructural characterization of snow, firn and ice in the future are briefly outlined. This article is part of the theme issue ‘The physics and chemistry of ice: scaffolding across scales, from the viability of life to the formation of planets’.