Using simultaneous three colour X-ray mapping and digital-scan-stop for rapid elemental characterization of coal combustion by-products.

A system is described for rapid, simultaneous three colour elemental mapping with a scanning electron microscope (SEM) and an energy dispersive X-ray analyser. The technique, which use a SEM scanning at TV rate, minimizes the disadvantages of long scan times such as inefficient use of linear amplifer and observable dead-time shadowing. The system also employs a digital scan-stop assembly utilizing a light pen to rapidly and reproducibly direct the beam to an object of choice for spot-mode analysis. Application of the system to analysis of fine particulates with emphasis on fly ash derived from coal-fired electric power plants is discussed. Chemical heterogeneity of fine particles in standard reference material fly ash and in phagocytized fly ash within pulmonary macrophages is demonstrated. This system combines the morphologic capability of the SEM with X-ray multielement mapping to provide a needed tool for particulate source identification.