Huntington, J.C., Ptasienski, J.J., Bunker, K.L., Strohmeier, B.R., Van Orden, D.R., and Lee, R.J., "A New Method for Fracturing Mineral Particles for Cross-Sectional FESEM Analysis", Periodico di Mineralogia, Vol. 77, No. 2, pp. 43-50, 2008.
AbstractThis work involves a novel approach for the preparation and characterization of cross-sectional samples of mineral particles and asbestos fibers. The unique sample preparation method involves embedding and fracturing the fibers across the length of the fiber. The morphology and characteristics of the fiber cross-sections are directly observed in a field emission scanning electron microscope (FESEM). Dimensions of the fiber cross-sections were measured from the images off-line using AnalySIS© Version 3.2 software.
In previous studies, the native ends of groups of fibers and individual crystals have been observed in the polarized light microscope (PLM) and the scanning electron microscope (SEM) [1-3]. This is the first study that involves fracturing the fibers along the length in order to view and measure freshly prepared cross-sections. A wide variety of mineral samples were prepared and analyzed, including South African crocidolite, West Greenland anthophylite, and the National Institute of Standards and Technology (NIST) amosite and chrysotile Standard Reference Materials (SRM).
A small sample of the fibers (Fig. 1a) was embedded in a 1.5 inch diameter Lucite® mount. The sample was cured for eight minutes in a Buehler SimpliMet® 3000 Automatic Mounting Press at 360°F and 4200 psi. A band saw was used to cut two notches on either side of the fibers embedded in the puck (Fig. 1b). The Lucite mount was then mounted into a vice and the sample was fractured across the length of the fibers with a wrench (Fig. 1c). Prior to analyzing the cross-sectional sample in the FESEM, the sample was platinum coated for 1.5 minutes at 20 mA.
The fully prepared cross-sectional samples were analyzed in an FEI Sirion 400 FESEM instrument operated in the "ultrahigh resolution" mode with a Through-the-Lens Detector (TLD) and an accelerating voltage of 3 kV, a beam current of 200 pA, and a 4.0 mm working distance. Figure 2 a) and b) are FESEM secondary electron (SE) images of the NIST amosite cross-sectional sample. Figure 2 c) and d) are FESEM SE images of a crocidolite cross-sectional sample. The SE images of the amosite and crocidolite reveal cross sections with a wide variety of shapes, surfaces, and growth directions. In addition, both samples display some fibers exhibiting curvature. Measurements of the fiber cross-sections show a range of sizes depending on the sample under study.
The new sample preparation method described has proven to be very consistent and repeatable in providing suitable cross-sectional mineral samples for FESEM analysis. Observing cross-sections of mineral fibers in the FESEM provides information on the shape, dimensions, and crystal growth that is difficult to obtain with other preparation methods and analytical techniques.
References
1. Bandli, B.R., Gunter, M.E., The Microscope, 49 (2001) 191.
2. Sanchez, M.S., M.S. Thesis, University of Idaho, 2007.
3. Addison, J., McConnell, E.E., Proceedings of the International Symposium on the Health Hazard Evaluation of Fibrous Particles Associated with Taconite and Adjacent Duluth Complex, 2005.
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