Asbestos Microdiffraction with a High-Voltage Electron Microscope

Abstract

Conventional transmission electron microscopes (TEM) are the most commonly used analytical tools for positive identification and quantitation of asbestos in air and water samples. Selected-area electron diffraction (SAED), the accepted method of asbestos identification, often cannot yield identifiable diffraction patterns from chrysotile asbestos fibers smaller than 0.1-μm diameter. Beaman and Baker introduced microdiffraction for positive identification of 0.02-μm diameter chrysotile fibrils but this focused-beam technique is optimal only with strongly demagnifying triplecondenser TEM's.The small wavelength of the electron beam generated by high-voltage electron microscopes (HVEM) has distinct advantages for diffraction studies. The Ewald sphere at l000kV is approximately four times larger than the sphere of a l00kV beam and consequently intersects and projects more widespread points from a given plane in the reciprocal lattice. Furthermore, the beam can penetrate thicker specimens than conventional TEM's. We have assessed the capability of a double-condenser 1200kV HVEM (AEI EM7) to identify asbestos by microdiffraction.