Fig. 5
High spatial resolution electron microprobe back-scattered electron images and elemental maps (Ca, Mg, Fe, S, Si) from the basal sections of two different scale-fragment samples (a, b). The precipitated scale material consists of homogeneous Mg-calcite indicated by the measured Ca and Mg concentrations. The basal corrosion layer primarily consists of iron sulfide minerals (Fe and S concentrations) resulting from gradual alteration of the conventional steel (pink color indicating high elemental concentration on relative color range). Elevated silica contents (Si) are typically associated with the Fe-sulfide layers. Note the frequent occurrence of cracks displacing sulfide corrosion products and related scale carbonate (red arrow in BSE image)