Environmental Engineering Reference
In-Depth Information
By stopping the primary beam scanning and moving the emission of primary
electrons toward a preselected area on the SEM image, the emission of an X-ray
spectrum typical of the chemical elements constituting the microsurface is collected.
Analysis of the spectrum also allows the quantification of these elements by
comparing the intensity of the spectrum peaks with those of standard spectra. The
phases detected with SEM or X-ray diffraction can thus be quantified with this
method.
Figure 10.4.
Cloister of the church Saint Trophime, Arles. Superficial deposits on
marble columns. Thin sections observed under optical microscope and corresponding X
mappings. The associations of the elements Si, Ca and S enable us to reconstruct the history
of these columns. A: a calcite incrustation was covered by a layer rich in silica (residues of a
silicatization treatment). The most recent deposit, rich in Ca and S, is a black crust (see
Chapter 8, section 8.3.2.3). B: the same stratigraphy but an ancient atmospheric deposit
comes in between the calcitic encrustation and the silicatization residues. This atmospheric
deposit is rich in silicon because it had been impregnated with amorphous silica during the
application of the silicatization treatment [VER 94]
By moving the sample, profiles of its chemical composition are collected. It is
also possible, with the help of this microprobe, to get X-ray images showing the
distribution of one or more chemical elements on the surface. It is possible to use
specific image analysis software (see Figure 10.4) to observe the decreasing amount
of sulfur in black crusts with increasing distance from the sample surface. It is also
possible to detect old silicatization treatments by creating an image showing just the
silicon. This is known as a silicon image (many French monuments were treated
