Abstract
Plasma electrolytic oxidation (PEO) process was employed for preparing oxide coatings on AA2024 aluminum alloy in solutions containing Zn-Al layered double hydroxide (LDH) particles. Sodium hexametaphosphate aqueous solution was selected as the standard solution, based on its almost neutral pH value considered as important for the LDH stability. Different additives to the standard solution were examined including 2-mecaptobenzothiazole (MBT) and different Zn-Al LDH compounds. The formed coatings underwent characterization regarding their morphology, chemical and phase composition, as well as assessment of their photocatalytic and corrosion protection efficiency. Coating thickening and compactness evolution were noted for all coatings with LDH additions to the standard solution. Obtained coatings are well-crystallized featuring γ-Al2O3 and two Zn-containing crystalline phases, namely ZnO and NaZnPO4, originating mainly from the LDH addition to the solution. PEO coatings obtained in this study demonstrated very reasonable photocatalytic activity for immobilized photocatalyst, reaching 51 % after 6 h under UV irradiation. The inclusion of Zn-Al LDH substantially boosted the impedance modules at low frequencies by two orders of magnitude compared to bare AA2024 alloy when exposed to a 3.5 % NaCl solution.
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