Insight into the Role of Cerium (III) Addition to a MgAl-LDH Coating on AA6082

Abstract

In this work, Ce doped MgAl-LDHs layers have been developed through an in-situ synthesis method on 6082 aluminum surface. The aim was to gain mechanistic insight into the role of Ce(III) as an active corrosion inhibitor embedded in the LDHs layer. The development of the LDH structure was verified by checking the presence of the characteristic XRD peaks, the platelet morphology (evaluated by SEM-EDXS) and the functional groups (by FTIR-ATR analyses). The same techniques were employed to assess the effect of a prolonged immersion time in 0.1 NaCl on the Ce doped MgAl-LDH coatings. Electrochemical impedance spectroscopy (EIS) was employed to monitor the evolution of the electrochemical properties of the coatings during prolonged immersion in saline solutions. The findings suggest a crystallization/dissolution/precipitation mechanism which implies: (i) the formation of crystalline cerium compounds, such as Ce(OH)3, in the LDH structure during the synthesis; (ii) the dissolution upon exposure to the NaCl solution, thus leading to cerium ions release; (iii) the precipitation of amorphous Ce oxides/hydroxides at the cathodic sites when the metal starts to corrode; (iv), the consequent mitigation of the electrochemical activity of the metal and, thus, the reduction of the extent of corrosion.

Cerium-based conversion films developed on LiAl-layered double hydroxide coatings for corrosion protection of AA7075 aluminum alloys

“…Iqbal and Fedel [30] applied Ce-doped MgAl LDHs directly on the anodized aluminum surface and on the hot-water sealed anodized aluminum specimens at 80 °C for 18 h. According to EIS investigations during immersion in 0.1 M NaCl solution for 1200 h, it was found that the addition of Ce ions facilitated improved corrosion protection, mainly when the growth of CeMgAl-LDHs has been developed on the anodized layer. To get more information on the role of trivalent cerium species present in Ce-doped MgAl LDHs, Fedel and Zampiccoli [31] developed the conversion layers directly on the 6082 aluminum alloy surface at 80 °C for preparation periods between 1 and 9 h. The analysis of the data acquired before and after 400 h of continuous immersion in the 0.1 M NaCl, suggested a corrosion inhibition mechanism based on the dissolution and re-precipitation of Ce compounds.…”