Automated Characterisation of Individual Carbonaceous Fly-Ash Particles by Computer Controlled Scanning Electron Microscopy: Analytical Methods and Critical Review of Alternative Techniques

Abstract

This paper describes the development of a technique to characterise carbonaceous fly-ash particles as part of a larger EU COPERNICUS project 'Fly-ash and metals in Europe: Implications for human and environmental health (FLAME)'. Source samples of fly-ash from 32 power stations covering five different fossil-fuel-types - coal, oil, peat, brown coal and oil shale were analysed by computer controlled scanning electron microscopy (CCSEM) with energy dispersive X-ray spectroscopy (EDS). A classification scheme was developed and used to apportion surface sediment samples from lakes or reservoirs in Estonia, the Czech Republic, Ireland and the United Kingdom. This paper discusses the analytical part of the FLAME project. As this was one of the first applications of this type of approach and utilises only one individual particle analysis method (CCSEM), other current techniques are reviewed to evaluate possible future improvements. Chemical analysis by other micro-analytical techniques, especially laser microprobe mass analysis (LMMS) and micro-particle induced X-ray emission (µ-PIXE) have been extensively reviewed by other authors. This work is summarised and aspects relevant to carbon particles are discussed. Particle shape characterisation is an area that has received a great deal of attention and remains very problematic for many complex anthropogenic and environmental particles. Considerable research has been undertaken using shape factors, fractals, Fourier transforms and neural networks. The final part of the paper reviews some of the more relevant developments in the area of shape description as it applies to particulate material, and especially carbonaceous particles of the type analysed in the FLAME programme.