# Dynamic Corrosion Test Using LiNO3 Containing Molten Salt for CSP Applications
## 3 Results and Discussion  
Table 4 shows the weight increments divided by the surface area of the samples. In the case of A516 carbon steel the weight increases between 200 h and 600 h and remains constant at times higher than 600 h.  
Superficial SEM characterization of the surface of the samples at 200 h and 600 h was performed. In the case of A516 (Figure 2), the image at 200 h (left) shows a uniform corrosion layer with a small area (spectrum 1) without corrosion, detecting the base material in the EDS analysis. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Alloy** & \multicolumn{3}{c}{**\(\Delta\)m/S (mg:cm\({}^{-2}\))**} \\ \hline A516 & 200 h & 600 h & 1000 h \\ \cline{2-5}  & 0.2677 & 0.3231 & 0.3155 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Weight change per surface area of the samples removed after 200 h, 600 h and 1000 h exposure in the corrosion test at 390 \({}^{\circ}\)C.  
Figure 2: Backscattered surface image CS A516 at 200 h (**Left**) and 600 h (**Right**). The corrosion layer is mainly composed by Fe-O with magnesium content as an active impurity from the salt [16]. Cross sectional study was analyzed at the end of the test (1000 h) and it is shown in Figure 3.  
The corrosion layer thickness was measured from Figure 3, taken at different distances from the edge of the sample (2 mm, 6 mm, 10 mm, 14 mm and 18 mm). The average thickness was considered as the layer thickness. This procedure was also repeated at the intermediate measure times. Table 5 shows the thickness of A516 at different times (200 h, 600 h and 1000 h). In average, the corrosion layer thickness increases until 600 h and remains constant between 600 and 1000 h.  
The velocity of corrosion is 1.70\(\cdot\)10\({}^{-3}\)\(\upmu\)m/h that corresponds to 0.015 mm/year. Attending to the recommendations of [PERSON] et al. [17] (Table 6), this material would be recommended for long term service. However, additional corrosion test with longer exposure times are recommended. The profile of compositions was analyzed by SEM. Figure 4 shows the concentration of Fe (blue) and O (red) as a function of the distance from the surface of the steel. Three zones can be observed in the pictures. Zone I (0.2 \(\upmu\)m) contains higher amount of oxygen, since Fe diffusion is lower in this outer zone. Zone II shows similar concentrations of Fe and oxygen. It is possible that the principal compound in this zone is Fe\({}_{2}\)O\({}_{3}\). Zone III shows a different pattern, the content of Fe increases and the oxygen one decreases. This could be due to the evolution of hematite (Fe\({}_{2}\)O\({}_{3}\)) to magnetite (Fe\({}_{3}\)O\({}_{4}\)). A clear transition in the gray tonality is detected between Zone II and Zone III in Figure 5 (right). Figure 3: Backscattered cross section study in corrosion layer of A516 at 1000 h of immersion in LiNO\({}_{3}\) ternary molten salt at 390 \({}^{\circ}\)C. \begin{table}
\begin{tabular}{c c c c} \hline
**Distance** & **Thickness (\(\upmu\)m) at 200 h** & **Thickness (\(\upmu\)m) at 600 h** & **Thickness (\(\upmu\)m) at 1000 h** \\ \hline
2 mm & 1.40 & 1.74 & 1.5 \\
6 mm & 1.52 & 1.72 & 1.42 \\
10 mm & 1.50 & 1.56 & 1.74 \\
14 mm & 0.96 & 1.80 & 1.88 \\
18 mm & 1.04 & 1.80 & 1.98 \\ ave & 1.28 & 1.72 & 1.70 \\ S\({}_{\mathrm{n-1}}\) & 0.26 & 0.10 & 0.24 \\ \hline \end{tabular}
\end{table} 
Table 5: Thickness of the corrosion layer at different times in \(\upmu\)m.  
In order to complete the corrosive characterization, a XRD analysis was carried out in the A516 steel at the end of the test (Figure 5).