Article

A technique for the examination of polar ice using the scanning electron microscope.

British Antarctic Survey, Natural Environmental Research Council, High Cross, Madingley Road, Cambridge, CB3 0ET, UK.
Journal of Microscopy (Impact Factor: 1.63). 03/2002; 205(Pt 2):118-24. DOI: 10.1046/j.0022-2720.2001.00981.x
Source: PubMed

ABSTRACT The microstructure and location of impurities in polar ice are of great relevance to ice core studies. We describe a reliable method to examine ice in the scanning electron microscope (SEM). Specimens were cut in a cold room and could have their surfaces altered by sublimation either before (pre-etching) or after (etching) introduction to the cryo-chamber of the SEM. Pre-etching was used to smooth surfaces, whilst etching stripped away layers from the specimen surface, aiding the location of particles in situ, and allowing embedded structures to be revealed. X-ray analysis was used to determine the composition of localized impurities, which in some cases had been concentrated on the surface by etching. Examining uncoated surfaces was found to be advantageous and did not detract from qualitative X-ray analysis. Imaging uncoated was performed at low accelerating voltages and probe currents to avoid problems of surface charging.

0 Bookmarks
 · 
50 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: 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.
    Proceedings of the Institution of Mechanical Engineers Part L Journal of Materials Design and Applications 01/2007; 221(3):151-156. · 0.56 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The suitability of secondary ion mass spectrometry (SIMS) for the analysis of polar ice is assessed. A magnetic sector SIMS instrument, modified to permit analysis of cryogenically prepared specimens, was used to analyze a sample of naled ice from in front of midre Lovénbreen, Svalbard. The ion-induced secondary electron imaging capability of the instrument permitted identification of features such as grain boundaries, triple junctions, filaments, pore spaces and cracks. Secondary ion maps were acquired with sub-micron resolution, permitting the characterization of chemical impurities at grain boundaries. Two regions of interest were analyzed and are described in detail. In the first, discrete particles of impurity (possibly precipitates) containing Na, Mg, K and Cl were identified along a grain boundary. Additionally, Mg was found to be present along the full length of the boundary. In the second analysis, impurity containing Na, Mg, K and Cl was found at a triple junction and some evidence for segregation of impurity to grain boundaries was gained. In both regions of analysis, Na, K and Cl were more apparent in grain interiors than Mg, despite the presence of the latter element at the boundaries. Results corroborate previous scanning electron microscopy with energy-dispersive X-ray spectrometry (SEM-EDS) observations.
    Journal of Glaciology 12/2006; 53(180):63-70. · 2.88 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: For many years, the microstructural characterization of ice and firn has used optical microscopy often involving observation of thin sections between crossed polarizers. However, such an approach, in addition to being of low resolution, does not provide complete information on the microstructure. In previous work (Obbard et al. 2003), we have shown how scanning electron microscopy coupled with X-ray microanalysis can be used to determine the microstructural location of impurities in ice cores. In this paper, we outline the use of scanning electron microscopy-based techniques to determine the 3-D orientation of grains and, thus, enable more complete analysis of the orientation relationships between grains in ice and firn. In addition, we show how scanning electron microscopy can be used to determine the internal surface area, porosity and grain size in firn.