Corrosion protection of aluminum by smart coatings containing layered double hydroxide (LDH) nanocontainers

In this study, the LDH containing a kind of green inhibitor (sodium molybdate) was synthesized and utilized in a poly-vinyl alcohol (PVA) base coating applied on the aluminum (5054 series) surface. After evaluating the LDH performance, the inhibitor release from the LDH crystals was examined by changing significant parameters like MII/MIII (the molar ratio of divalent ions into trivalent ions), pH, aging time and temperature. In order to find the kinetic release of intercalated inhibitor a prediction model was introduced in 3.5% NaCl solution. The model expressed that the pH as the processing parameter has special effect on the kinetic releasing of the inhibitor. It can enhance the amount of released inhibitor up to 6 times larger due to its effect on the LDH morphology and structure. Also MII/MIII has serious effect on the amount of intercalated inhibitor and the release rate. In fact, the ratio alteration can affect the amount of final released inhibitor by a factor of 2 and its interaction with the pH is noticeable. The whole mechanism of releasing was recognized as Fickian diffusion and the released data were well fitted with the Weibull model. Corrosion measurements show the mechanism activation of the synthesized smart coating and improvement of the corrosion properties (the polarization resistance has been enhanced more than 3 times) in compare with the regular coatings. More LDH in the coating network result in better resistance (39,250 Ω cm−1) to corrosion for the produced coating up to approximately 5.7 wt% of the Cl− ions.