scholarly journals Shallow-ice microstructure at Dome Concordia, Antarctica

2000 ◽  
Vol 30 ◽  
pp. 8-12 ◽  
Author(s):  
Laurent Arnaud ◽  
Jérôme Weiss ◽  
Michel Gay ◽  
Paul Duval
Keyword(s):  
Crystal Size ◽  
Accumulation Rate ◽  
Ice Core ◽  
Processing Technique ◽  
Image Processing Technique ◽  
Size Distributions ◽  
Thin Sections ◽  
Crystal Size Distributions ◽  
Size Profile ◽  
The Mean

AbstractThe shallow-ice microstructure at Dome Concordia, Antarctica, has been studied between 100 m and 580 m. An original digital-image-processing technique has been specially developed to extract ice microstructure (grain boundaries) from thin sections prepared during the two first scientific EPICA field seasons (1997/98 and 1998/99). Using this, not only the mean crystal size, but also crystal-size distributions and shape anisotropy were determined. The mean crystal-size profile as well as crystal-size distributions reveal normal grain growth up to 430 m. Between 430 m and 500 m, a marked decrease of crystal size is observed and compared with a similar trend obtained in the "old" Dome C ice core formerly associated with the Holocene/Last Glacial transition (Duval and Lorius, 1980). This seems to indicate a slightly lower accumulation rate (by <10%) at Dome C. The shapes of the crystal-size distributions, though very similar, do evolve with depth and seem to be sensitive to climatic changes. An increasing flattening of crystal shape is observed with depth. This allowed estimation of the vertical strain rate in the shallow part of the ice sheet.

Application of an Empirical FBRM Model to Estimate Crystal Size Distributions in Batch Crystallization

2014 ◽  
Vol 14 (2) ◽  
pp. 607-616 ◽  
Author(s):  
Huayu Li ◽  
Yoshiaki Kawajiri ◽  
Martha A. Grover ◽  
Ronald W. Rousseau
Keyword(s):  
Crystal Size ◽  
Size Distributions ◽  
Batch Crystallization ◽  
Crystal Size Distributions

Transient Nucleation in Co-Zr Metallic Glasses

1985 ◽  
Vol 57 ◽  
Author(s):  
Uwe Köster ◽  
Margret Blank-Bewersdorff
Keyword(s):  
Electron Microscopy ◽  
Metallic Glasses ◽  
Crystal Size ◽  
Time Lag ◽  
Size Distributions ◽  
Quantitative Electron Microscopy ◽  
Crystal Size Distributions ◽  
Different Temperatures ◽  
Transient Nucleation ◽  
Good Agreement

AbstractCrystallization kinetics and crystal size distributions in Co33Zr67-glasses have been analyzed by quantitative electron microscopy. The polymorphic crystallization of spherical CoZr2 crystals is very suitable reaction for such an analysis. Calculated crystal size distributions at different temperatures were compared to those experimentally revealed. Parameters controlling crystallization were varied within reasonable limits until theoretically calculated and experimentally observed crystal size distributions were in good agreement. It has been found that crystal size distribution can be explained by transient nucleation; the time lag and its temperature dependence can be evaluated. These results are discussed in the light of recent theories on transient nucleation.

Texture constraints on crystal size distribution methodology: An application to the Laki fissure eruption

2020 ◽  
Vol 105 (5) ◽  
pp. 585-598
Author(s):  
Kim A. Cone ◽  
Richard F. Wendlandt ◽  
Katharina Pfaff ◽  
Omero F. Orlandini
Keyword(s):  
Electron Microscopy ◽  
Size Distribution ◽  
Crystal Size ◽  
Crystal Size Distribution ◽  
Size Distributions ◽  
Backscatter Electron ◽  
Crystal Length ◽  
Crystal Size Distributions ◽  
Length Measurements ◽  
Scanning Electron

Abstract Modeling crystal size distributions often requires the extraction of 2D discrete crystal lengths to calculate 3D volumetric equivalences. These apparent lengths are obtained from digital images that exploit different physical and chemical characteristics of samples, and the choice of image type can affect the interpretation of crystal length measurements, thus affecting crystal size distribution modeling. To examine method- and texture-based effects on extracting crystal size distributions, we obtained plagioclase length measurements from two texturally opposing basaltic lava samples from the well-documented Laki fissure eruptions of 1783–1784. Using approaches that consider inherent texture-based limitations of 2D image types, we employed manual tracing and imaging software to extract plagioclase crystal lengths from three types of images: (1) photomicrographs from polarized-light microscopy, (2) backscatter electron images from scanning electron microscopy, and (3) energy-dispersive X-ray maps from automated mineralogy. Our results demonstrate that (1) phenocrysts (L ≥ 150 μm) and groundmass plagioclase (L &lt; 150 μm) in our basalt samples appear with multiple aspect ratios, while the latter also display greater nucleation densities as crystal size population are continuously refined over increasingly smaller crystal lengths; (2) complex crystal clusters must be manually dissected into their discrete crystal components to produce meaningful crystal size distributions; (3) localized electron backscatter diffraction analysis reveals mild preferred orientation in complex clusters and groundmass, the latter confirmed by variations in crystal size distributions between orthogonal backscatter electron images; and (4) method-induced variations in both aspect ratio and crystal length determination can produce a wide range of kinetic interpretations that pose challenges for cross-research comparisons. For phenocrysts, compensating for clustering and fracturing through manual tracing remains the most effective method, while groundmass populations can be addressed with high-resolution (micrometer-scale) automated scanning electron microscopy for deciphering late-stage eruptive behavior. A texture-focused protocol should be established, as any kinetic information derived from crystal size distribution analyses across multiple studies employing multiple approaches cannot otherwise be directly compared.

scholarly journals A model of crystal-size evolution in polar ice masses

2014 ◽  
Vol 60 (221) ◽  
pp. 463-477 ◽  
Author(s):  
Felix NG ◽  
T.H. Jacka
Keyword(s):  
Crystal Growth ◽  
Dislocation Density ◽  
Grain Boundary ◽  
Crystal Size ◽  
Boundary Migration ◽  
Ice Core ◽  
Ice Cores ◽  
Grain Boundary Migration ◽  
Shallow Subsurface ◽  
The Mean

AbstractIn the deep ice cores drilled at the GRIP, NGRIP and GISP2 sites in Greenland and at Byrd Station and the summit of Law Dome in Antarctica, the mean crystal size increases with depth in the shallow subsurface and reaches steady values at intermediate depth. This behaviour has been attributed to the competition between grain-boundary migration driven crystal growth and crystal polygonization, but the effects of changing crystal dislocation density and non-equiaxed crystal shape in this competition are uncertain. We study these effects with a simple model. It describes how the mean height and width of crystals evolve as they flatten under vertical compression, and as crystal growth and polygonization compete. The polygonization rate is assumed to be proportional to the mean dislocation density across crystals. Migration recrystallization, which can affect crystal growth via strain-induced grain boundary migration but whose impact on the mean crystal size is difficult to quantify for ice at present, is not accounted for. When applied to the five ice-core sites, the model simulates the observed crystal-size profiles well down to the bottom of their steady regions, although the match for Law Dome is less satisfactory. Polygonization rate factors retrieved for the sites range from 10–5 to 10–2 a–1. We conclude that since crystal size and dislocation density evolve in a strongly coupled manner, consistent modelling requires multiple differential equations to track both of these variables. Future ice-core analysis should also determine crystal size in all three principal directions.

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