# Insight into the Role of Cerium (III) Addition to a MgAl-LDH Coating on AA6082
## 3 Results
The peaks located at 551 and 760 cm\({}^{-1}\) are related to the translation modes of the hydroxyl group mainly attached to Al\({}^{3+}\). The associated deformation modes are represented by two signals at 943 and 1014 cm\({}^{-1}\). The absorption band found at 610 cm\({}^{-1}\) is assigned to the hydroxyl  
Figure 4: Deconvolution analysis of the ATR-FTIR spectra from (**a**) 3750 to 2750 cm\({}^{-1}\) and (**b**) 1100 to 500 cm\({}^{-1}\) of fresh sample C10-4.5. The Violet curve represents the sum of all deconvoluted signals. In black, the experimental curve. mainly to Mg\({}^{2+}\). The peaks at 656 and 870 cm\({}^{-1}\) are attributed to the asymmetric stretching modes of the interlayer carbonate groups. The relative percentage of the different chemical groups were found not to differ significantly with synthesis time (from 1 to 9 h). After the exposure in the electrolyte for 400 h, the lowering in peak intensity suggests the dissolution of the LDH coatings along with the release of ionic species. The peaks associated with the asymmetric stretching NO\({}_{3}^{-}\) at 1348 cm\({}^{-1}\) and the ONO bending vibration at 1397 cm\({}^{-1}\) disappear for the C10-4.5 and C10-9 samples, thus suggesting the release of the nitrogen compounds as a result of the intercalation of CI ions. The CI\({}^{-}\leftrightarrow\) NO\({}_{3}^{-}\) exchange is recognized to play a role in corrosion resistance as it is suggested that the nitrate-containing LDH coatings are effective nano-traps that can entrap chloride ions and, thus, postpone the initiation of the corrosion process [42]. Under the favorable conditions, the dissolved Mg\({}^{2+}\) ions could form hydroxy compounds, Mg(OH)\({}_{2}\), which can inhibit the spread of the pitting corrosion [65]. Interestingly, it is possible to observe the signal split at 1028 cm\({}^{-1}\) observable in C10-1 and C10-9 spectra, which is attributed by some authors [63] to the symmetric stretching of the carbonate CO\({}_{3}^{2-}\). However, in this case the corresponding increase in the signal of both the symmetric and asymmetric stretching vibration of CO\({}_{3}^{2-}\) at 1544 cm\({}^{-1}\) is not observed. Figure 5 shows the XRD patterns of the in situ developed LDH films. Between 10 and 45\({}^{\circ}\), it is possible to observe the characteristic peaks of LDH that confirm the hydrotalcite layer's presence, in accordance with the FTIR results. They have miller indexes (003), (006), and (009) and they are located at 13, 25.5, and 40\({}^{\circ}\), respectively [66]. Small signals are present at about 13, 27, and 32\({}^{\circ}\) that can be attributed to the formation of cerium hydroxide Ce(OH)\({}_{3}\) or oxide CeO\({}_{2}\)[48; 67]. The 2\(\theta\) range between 45 and 65\({}^{\circ}\) was omitted since it contains only reflections belonging to the Al substrate and intermetallic particles [68]. In the 2\(\theta\) range between 65 and 110\({}^{\circ}\), the peaks at 72 and 73\({}^{\circ}\) are distinctive of the cell planes (110) and (113). The \(d_{hkl}\) basal spacing and the crystal size \(D\) were calculated: the results are reported in Table 1. The FWHM parameter was used instead of the integral breath, and it was calculated by employing the OriginLab software. The reflection peak related to the plane (003) was used to measure \(c=3\cdot d_{003}\) and the plane (001) for \(a=2\cdot d_{110}\)[44]. Figure 5: XRD pattern from 10\({}^{\circ}\) to 110\({}^{\circ}\) of C10 series C10 in their fresh state (solid lines) and after 400 h 0.1 M of NaCl immersion (dashed lines). The XRD patterns collected after 400 h of immersion in 0.1 M NaCl are reported in Figure 5 as dashed lines. Looking at the low and high angle regions, it is clear that the signals belonging to the LDH structure have almost completely disappeared, thus suggesting the partial loss of crystallinity.