Characterization and analysis of individual fly-ash particles from coal-fired power stations by a combination of optical microscopy, electron microscopy and quantitative electron microprobe analysis

Abstract

Quantitative electron microprobe analysis has been used to determine the inorganic chemical composition of individual fly-ash particles previously categorized on the basis of properties recognizable by light and scanning electron microscopy. Seven categories may be recognized: 1. (1) unfused detrital minerals (principally quartz), 2. (2) irregular-spongy particles derived from partly-fused clay minerals, 3. (3) vesicular colourless glass (in the form of irregular particles and cenospheres) derived from viscous melts, 4. (4) solid glass (mostly in the form of spherical particles and sometimes pigmented) derived from fluid melts, 5. (5) dendritic iron oxide particles (mostly spherical) containing variable amounts of glass matrix, 6. (6) crystalline iron oxide particles (mostly spherical) containing minimal amounts of glass and 7. (7) unburnt char particles. The use of computerized energy dispersive X-ray analysis on the electron microprobe enables an analysis for all the inorganic elements present in a particle to be carried out simultaneously in about 60s. The rapidity and comprehensive nature of the procedure makes it possible to determine the composition of a large number of individual fly-ash particles in a relatively short time and thereby characterize the types and compositions that comprise the population.