The use of an analytical electron microscope in the analysis of mineral dusts

Abstract

Dust samples, whatever their source, usually consist of small quantities of very fine particles from which the following information is necessary: (a) the morphology of the mineral particles in the dust, i.e. size and shape; (b) the identity of the mineral particles in the dust; (c) the proportion of each mineral contained in the dust; (d) the mineral concentration in the sample of air, water or biological material from which the dust was recovered. Information is also required as rapidly as possible from a single preparation so that many samples may be analysed on a routine basis. This paper will outline how this information can be obtained by using an electron microscope analysis system. With such an instrument, dust particles of all sizes may be observed and their size and shape obtained, while the electron microprobe may be used to analyse single particles to determine their chemistry and identify them. The bulk chemistry of the dust may be obtained in a similar manner by analysing large numbers of particles simultaneously. By using the chemical data obtained from single particles and also the bulk chemistry of the sample, the mineral composition of the dust may be computed. A measure of the mass of dust being analysed can be obtained from a measurement of the X-ray count rate obtained during bulk analysis, measurement of the incident electron-beam intensity and reference to an instrument calibration curve.