Incorporation of Nanometer-Sized Layered Double Hydroxide with Anions that Improve the Corrosion Resistance of Epoxy Polymer

Layered double hydroxide (LDH) has been widely used as a two-dimensional nanomaterial in the corrosion protection of epoxy (EP) coatings due to its physical barrier properties and excellent ion exchange capacity. However, conventional LDH with an interlayer of NO3– (LDH-NO3) is prone to failure in corrosive environments due to its limited ion exchange ability. It is demonstrated in this work that, compared to an EP coating containing LDH-NO3 (EP/LDH-NO3), EP coatings containing ZnAl-LDH-MoO42– (EP/LDH-MoO4) and ZnAl-LDH-PO43– (EP/LDH-PO4) have stronger corrosion resistance and self-healing abilities. This is attributed to the trapping effect of corrosion anions between the LDH layers by the inhibitor ions, which prevents the direct contact of the corrosion anions with the substrate. In addition, the inhibitor ions can combine with metal ions from the substrate to form insoluble complexes in localized corrosion areas, thus blocking further deterioration. Furthermore, EP/LDH-MoO4 has superior corrosion resistance and self-healing properties compared to EP/LDH-PO4, as the more active MoO42– anions have a stronger ion exchange ability than PO43–. This study not only highlights the potential of inhibitor ions inserted in LDH layers for anticorrosion but also paves the way toward the design of more effective EP-based coatings.