Sealing post-treatments of plasma electrolytic oxidation coatings based on fibrous silica

This study investigates the hydrothermal sealing of plasma electrolytic oxidation (PEO) coatings on aluminium using fibrous silica (KCC-1) and Ce-modified KCC-1 particles (Ce-KCC-1). The in-situ growth of fibrous silica within the porous oxide layer enables deep penetration and chemical integration, forming a robust barrier against corrosion. This work presents a significantly enhanced sealing strategy for PEO coatings, demonstrating superior corrosion resistance and structural cohesion compared to existing post-treatment methods. The incorporation of cerium retained the fibrous morphology of KCC-1, with a slight reduction in particle size due to cerium ion hydrolysis by urea, which influenced silica condensation. Cerium-rich compounds (CeO 2 , Ce 2 O 3 , and CeCO 3 OH) formed during treatment were deposited as nanoparticles and sharp platelets on the silica surface. The Ce-KCC-1 post-treatment delivered substantial barrier enhancement during the initial 72 h of immersion, attributed to particle-induced compaction and cathodic inhibition by cerium ions. Additionally, Ce microstructural modification facilitated Cl − retention near the coating surface, mitigating chloride-induced degradation. Beyond 72 h, a decline in protective performance was observed, likely due to the structural disruption caused by CeCO 3 OH platelets. These findings demonstrate a scalable and multifunctional approach to extending the durability of lightweight alloy systems, with potential relevance across advanced corrosion-resistant applications. • Fibrous silica (KCC-1) was used to seal PEO coatings via hydrothermal synthesis. • KCC-1 sealing improved corrosion resistance by two orders of magnitude. • Ce-KCC-1 retained fibrous morphology but had smaller particles due to cerium hydrolysis. • Ce promoted local Cl − retention, mitigating chloride-driven coating degradation. • Barrier properties declined after 72 h due to sharp CeCO₃OH particles.