Synergistic corrosion prevention of mild steel bars in concrete using PANI and nano-clay modified epoxy coatings

Abstract

This study explores the efficacy of nano-reinforced epoxy coatings using four different silane-treated nano-clays (Montmorillonite-MMT, Organic Montmorillonite-OMMT (Cloisite®15A and Cloisite®30B) and Halloysite-HNT) in conjunction with polyaniline (PANI). PANI, being a good pigment material for anti-corrosion coatings, captures electrons from the metal surface, redirecting them away from the coating. The results show that nano-clay reinforced epoxy coatings perform better than pure epoxy coatings. This improvement is due to the nano-clay's barrier properties and the combined effect of polyaniline fragments, which align closely with the nano-clay particles within the coating. Pure epoxy coatings showed a corrosion initiation delay of 7–8 days, whereas PANI with Cloisite®30B extended this to 70–75 days. Moreover, ultrasonic guided wave signals for pure epoxy samples dropped to zero within 40 days, while those with PANI and Cloisite®30B retained 90 % of their signal strength after 90 days. Notably, the Cloisite®30B and PANI combination proved most effective, with intercalated nano-clay particles creating tortuous diffusion pathways that impede ion ingress and corrosion propagation. Additionally, the hydroxyl groups of Cloisite®30B endorse bonding between nano-clay and polymer matrix resulting in an impermeable network. Characterization results of silane-treated clays demonstrate successful grafting of the silane agent on the nano-clay structure, while FE-SEM images of different coatings display the dispersion of nano-fillers within the coating matrix. In essence, our research underscores the pivotal role of advanced nano-modified epoxy coatings in mitigating corrosion-induced structural degradation, thereby bolstering infrastructure resilience and longevity.