3.2.2. PIXE/PIGE

PIXE and PIGE maps are presented in Figure 12 for Li, Sr and Ba sections of the samples prior to NSS and after 500 h NSS. The PIGE results represent an average over approximately 60 μm depth perpendicular to the X-section of the coating, and thus the average over several particle diameters. The maps show that Li is locally concentrated into small regions typically 2–10 μm in size, reflecting the particle size distribution. There is also some suggestion that these features are themselves interconnected, since the smaller features tend to form larger extended structures, suggesting the presence of clusters of Li2CO3 particles [71]. In the sample that has not been exposed to NSS, there is a clean boundary between the primer and the mounting medium. After 500 h NSS exposure, there is a zone completely depleted of Li2CO3 particles in the surface of the primer, as determined by comparing the Li distribution with the Ba distribution, and indicated by the parallel white lines. The depth of this depleted zone is 11 ± 8 μm (Table 4). However, there are also regions where there is a local, selective removal of individual particles or clusters of particles of Li2CO3 that penetrate much deeper into the coating. While this cannot be directly confirmed from the PIXE/PIGE, since the Li2CO3 distribution prior to NSS exposure is unknown for any particular region, the SEM clearly shows voids quite deep within the coating, suggesting selective dissolution paths (Figure 9).

**Figure 12.** Three-colour maps of sections of the coating prior to NSS exposure and after 500 h exposure to NSS. These maps are combined PIGE (Li–Red) and PIXE, (Sr in Blue and Ba in green). Three colour elemental maps for Li-Cu-Ba (**a**) without NSS exposure and (**b**) after 500 h NSS exposure.
