K. E. Harris, K. L. Bunker, B. R. Strohmeier, R. Hoch, and R. J. Lee
The distinction between asbestos and non-asbestos amphibole particles is important from both a scientific and a regulatory standpoint. This study involved the development and application of an analytical protocol using transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), selected area electron diffraction (SAED), and field emission scanning electron microscopy (FESEM) techniques for the particle-by-particle characterization (i.e., chemistry, crystallography, and morphology) of mixed mineral dust. Recent breakthroughs in SEM technology have made FESEM a common and reliable tool in analytical laboratories and have allowed significant advances in the characterization of mineral fibers. Features key to distinguishing between asbestos and non-asbestos amphibole particles, such as overall particle shape and surface roughness, are readily apparent in FESEM images but difficult to determine when using TEM alone.
Particle-by-particle examination of multiple samples generates large volumes of TEM and FESEM images, EDS spectra, and SAED patterns. To facilitate data review, all images, spectra, and diffraction patterns were imported into a digital database. The database allows simultaneous viewing of multiple TEM and/or FESEM images, EDS spectra, and SAED patterns for a given particle. Mineral particles were classified by various categories, such as particle shape, end and side geometries, and surface texture. The database format allows querying and summarizing the various particle classifications and/or sub-classifications from a single sample or a group of samples. The organization and viewing capacity of the database were useful for reviewing and interpreting data, sharing technical results with other experts, and training new analysts.
This study demonstrated that FESEM is a valuable complimentary tool to TEM for characterizing the morphology and surface characteristics of amphibole particles suspected to be asbestos and that digital imaging and digital database utilization are essential elements for accurate characterization of complex mixed mineral dusts.
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