Quantitative analytical electron microscopy of metals and minerals

Abstract

For a thin specimen X-ray absorption and fluorescence can, to a first approximation, be ignored and observed characteristic X-ray intensity ratios, I A/I B, can be converted into weight fraction ratios, C A/C B by multiplying by a constant, k AB: C A C B = k ABI A I B . K AB values can be calculated or determined experimentally. X-ray absorption within the sample must be considered when there is a significant difference in the energy of the characteristic X-rays. Fluorescence effects due to continuum X-rays can be ignored in thin specimens and characteristic fluorescence is much less than that observed in bulk specimens. Expressions are given for both the absorption and fluorescence corrections. Beam spreading has been calculated in a mineral at 100 kV using models based on Rutherford-scattering, plural-scattering and Monte-Carlo theory. The calculations are compared with experimental results. The application of AEM to metals is illustrated by the study of partitioning of Si, Mn and Cr in the pearlite reaction. Because most minerals are composed predominantly of light elements, absorption and fluorescence can be ignored for a wide range of thicknesses. Applications in mineralogy are illustrated by examples from particle analysis (e.g., asbestos) and by the study of the precipitation of a cellular intergrowth of pyroxene and spinel in olivine.