Scanning electron microscopy and transmitted electron backscatter diffraction examination of asbestos standard reference materials, amphibole particles of differing morphology, and particle phase discrimination from talc ores

Our plain-English summary of Scanning electron microscopy and transmitted electron backscatter diffraction examination of asbestos standard reference materials, amphibole particles of differing morphology, and particle phase discrimination from talc ores, by B.R. Bandli, M.E. Gunter (Microscopy and Microanalysis, 2014).

The study

• Authors: B.R. Bandli, M.E. Gunter
• Journal: Microscopy and Microanalysis
• Published: 2014;20(6):1805-16
• Cited by: 4 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Since 1972, when the US Occupational Health and Safety Administration established the first limits on occupational exposure to asbestos fibers, numerous analytical methods employing several microscopy techniques have been developed to identify a group of minerals defined by legislation as asbestos. While transmission electron microscopy (TEM) is implemented in standardized analytical methods, these methods specify the use of selected area electron diffraction. Because of this constraint, the diffraction data a TEM can provide are often underutilized due to challenges associated with collecting and interpreting individual diffraction patterns. It has been shown that transmission electron backscatter diffraction (tEBSD) produces diffraction patterns nearly identical to electron backscatter diffraction, but from smaller crystal domains. This paper explores the utility of tEBSD for characterization of asbestiform particles from reference asbestos materials, a suite of amphibole minerals of varying morphologies to determine if there is a correlation between mineral habit (i.e., crystal form), microscopic particle shape preferred orientation, and mineral specimens from an industrial talc deposit to provide a case study of the utility and limitations of the technique.

In plain English

This laboratory study tested whether transmission electron backscatter diffraction (tEBSD), a scanning electron microscope technique, combined with chemical analysis, can identify asbestos and related mineral particles. The authors examined NIST asbestos reference materials, six tremolite samples ranging from asbestiform to massive habit, and five rock samples from the Gouverneur talc district in New York. Among elongated particles from the five amphibole reference materials, the share that produced indexable diffraction patterns ranged from 97% for tremolite (98 particles) to 47% for anthophyllite (101 particles). The smallest particle width that gave a result was 130 nm. Asbestiform tremolite showed a qualitative tendency to settle in a preferred crystal orientation. However, the source habit of any single particle could not be determined from one tEBSD measurement using this deposition technique. Twinning was seen in tremolite asbestos and amosite. In the talc rocks, tremolite was identified in all five samples. Very few magnesium silicate particles gave usable patterns, so talc, anthophyllite and serpentine minerals often could not be told apart. The authors concluded that tEBSD can complement standard TEM methods, with limitations for minerals from talc deposits. The study did not examine health effects.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Laboratory mineral-analysis (microscopy methods) study using scanning electron microscopy, energy dispersive x-ray spectroscopy (EDS) and tEBSD
• Who was studied: Mineral samples, not people: NIST standard reference materials SRM 1866a (chrysotile, grunerite, riebeckite) and 1866b (tremolite, actinolite, anthophyllite); six tremolite specimens of asbestiform, acicular and massive habits; five rock samples from the Gouverneur talc district, New York State (including the Arnold Pit mine site and a former underground talc mine near Talcville)
• Exposure: No human exposure was studied. The materials examined were asbestos reference minerals (grunerite/amosite, riebeckite/crocidolite, tremolite, actinolite, anthophyllite, chrysotile), tremolite of different habits, and talc ores containing talc, tremolite, anthophyllite and a serpentine group mineral
• Main results:
  • Percent of amphibole reference-material particles (aspect ratio greater than 3 to 1) successfully indexed by tEBSD: tremolite 97 (n = 98), actinolite 85 (n = 100), amosite (grunerite) 76 (n = 100), crocidolite (riebeckite) 59 (n = 101), anthophyllite 47 (n = 101)
  • The smallest particle width that produced an indexing result was 130 nm
  • The authors stated that chrysotile and anthophyllite asbestos may not be reliably differentiated by SEM, EDS and tEBSD when no diffraction is observed from a particle
  • Asbestiform tremolite showed a qualitative tendency toward a strong preferred orientation of the {100} planes parallel to the substrate; massive samples showed this less
  • Whether a single particle came from an asbestiform or a massive sample could not be determined from a single tEBSD measurement with the deposition technique used. The authors said it could be used to describe the source habit of a population of particles
  • Parallel twinning was observed in tremolite asbestos and amosite fibers
  • In the five talc district samples, talc, tremolite and anthophyllite were identified by tEBSD. Tremolite was found in all five samples, talc only in sample AP_mass_talc, and anthophyllite only in sample TV_plates
  • Very few talc-ore particles composed of magnesium, silicon and oxygen produced usable diffraction patterns. Without a usable pattern, talc, anthophyllite and serpentine group minerals could not be distinguished
• The authors' conclusion: The authors concluded that EBSD and tEBSD can be used alongside TEM methods for asbestos fiber identification, and that the technique had some limitations with magnesium silicate minerals from a talc deposit
• Limitations the authors state:
  • tEBSD sometimes did not provide usable data
  • With the deposition technique used, tEBSD could not identify the source habit of an individual particle
  • The technique had limitations with magnesium silicate minerals from a talc deposit
  • The study used a tungsten filament SEM; the authors note a field emission SEM may allow smaller fibers to be characterized

Topics

Medical terms in this study, explained in our Lexicon: Scanning Electron Microscopy (SEM), Electron Backscatter Diffraction (EBSD), Amphibole Group, Talc, Occupational Exposure, Transmission Electron Microscopy (TEM), Selected Area Electron Diffraction (SAED), Asbestiform.

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