EMU Volume 9 – Chapter 7

Chapter 7: Electron microbeam analysis techniques used for the characterization of industrial minerals

M.I. Pownceby and  C.M. MacRae

Electron microbeam techniques such as Scanning Electron Microscopy (SEM), Electron Probe Microanalysis (EPMA) and Transmission Electron Microscopy (TEM) are commonly used in the characterization of industrial minerals providing morphological, chemical and structural information down to the atomic scale. The principal advantage of the electron microscope over the light microscope is the much improved resolution, due to the very low wavelength of the energetic electron (,1 A° ) compared to the visible light, which is employed in the optical microscope. A key advantage of microbeam instruments is the generation of X-rays from the interaction of electron with the sample thereby allowing both the identification of elements present through observation of the KLM X-ray lines and determination of the elemental composition when matrix affects are taken into consideration.

In this chapter an overview of the two main classes of electron microscopy, scanning and transmission, is presented, including a description of the instrumentation required and a discussion of their similarities and differences. The chapter also includes detailed information regarding the generation, detection and measurement of the various signals within the SEM and EPMA, the two instrument techniques most common to mineralogists. Finally, several case studies highlighting the use of these two electron microbeam techniques in the characterization of industrial minerals are presented. The examples were chosen to both illustrate traditional areas of use and emerging areas of application and include; automated SEM techniques, electron backscattered diffraction, charge contrast and in situ SEM imaging, EPMA mapping techniques, the determination of chemical states in minerals and materials using changes in X-ray peak shape, hyperspectral EPMA, and trace-element speciation using quantitative cathodoluminescence.

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