Electron Microscopy Based
Particle Analysis

Particle Morphology

Basic information on the nature and origin of particulate material can often be gathered from the size, shape and/or surface form of the individual particles. This type of information can be readily obtained by examining the particles in the scanning electron microscope (SEM). When a sample of particulate material is placed in the electron microscope it is non destructively bombarded by a finely focused beam (probe) of electrons. As the sample is irradiated by this stream of primary electrons a variety of interactions occur with the atoms in the sample. As a result, various forms of radiation are released from the sample which, when detected and processed, can be used to determine its constituent components. The three types of emitted signal most commonly used in individual particle analysis (IPA) are: secondary electrons, backscattered electrons and characteristic X-rays. The secondary electrons produced by the sample are used routinely to characterize PARTICLE MORPHOLOGY. These sample electrons are used to create unique, large depth of field, secondary electron images (SEI). The SEI provides information on the size, shape, and surface topography of individual environmental particles ranging in size from <1 micrometer (µm) to >1 millimeter.

Particle morphology is an important descriptor in IPA. This is because particle shape is frequently indicative of composition and/or origin.

High temperature urban/industrial combustion processes typically produce waste particles which are spherical in form.

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In coal burning power plants following the combustion phase the impurities in the coal almost invariably emerge as completely spherical particles.

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Combustion processes which generate carbon(aceous) particles (such as oil burning power plants) produce spherules which are well rounded and have a distinctive porous texture.

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Many raw materials released into the environment exhibit distinctive shapes which are indicative of an original formation process.

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Particles may be irregular in appearance as a result of natural or anthropogenic abrading processes. Angular fractured grains are produced by mining and milling processes.

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The form in which mineral particles originally crystallized is often highly characteristic. Asbestos minerals for example typically crystallize as long thin fibers.