Corrosion inhibition of galvanized steel by LDH-inhibitor hybrids Mechanisms of Inhibitor Release and Corrosion Reactions
Protection mechanisms of layered double hydroxide (LDH) anticorrosion coatings on galvanized steel were investigated. On the first step, the mechanisms of the action of MoO42-, L-cysteine and L-phenylalanine as water soluble inhibitors were verified. MoO42- showed the best performance associated with the rapid (less than 2 s) formation of Mo(V)-rich films on Zn surface in alkaline solutions. On the second step, factors affecting the release of MoO42- from Zn2Al/-LDH were identified. Presence of only Cl- in the solution resulted in a less than 40 % release of MoO42- after 24 h of the immersion with the Fick’s diffusion inside LDH controlling the overall process. Addition of carbonates resulted in the complete release after 1 h with the change of the release kinetics attributed to the surface controlled reaction. The immersion tests of coated samples showed slight inhibiting effect of MoO42-/LDH anticorrosion coatings in Cl- and high in CO32- solutions coherent with higher level of MoO42- released.