Abstract:

Aluminum phosphate coatings containing different levels of Cu²⁺ ions (Cu/Al molar ratio: 0.025, 0.05, 0.1) were prepared on 316-stainless steel based on the curing reaction of monoaluminium phosphate (MAP). The curing behaviors of the starting materials and phase compositions of the cured products were studied by differential scanning calorimetry and X-ray diffraction, respectively. Results indicate that the copper-free MAP cures at ≤250℃ to form 3 major phases: AlH₂P₃O₁₀·2H₂O, AlPO₄, and Al₈H₁₂(P₂O₇)₉. When Cu²⁺ ions are introduced into the MAP, an additional phase of Cu₂P₂O₇ appears in the cured product. E. coli was inoculated on the surfaces of coatings to evaluate their antibacterial properties. After co-culture with E. Coli for 12 h, all Cu²⁺-containing coatings exhibit antibacterial effect and show a positive association between Cu²⁺ content and antibacterial activity. After co-culture for 24 h, no viable bacteria remain on any Cu²⁺-containing coating. The addition of ethylenediaminetetraacetic acid to the culture medium substantially inhibits the antibacterial activities of all coatings, confirming that the antibacterial effect is attributed to the release of Cu²⁺ ions from coatings. Pull-out tests show that the bonding strengths of the coatings range between 14.5-18.1 MPa. Potentiodyanmic polarization indicates that the coatings reduce the corrosion current density of the stainless steel substrate by approximately two orders of magnitude.

Key words: copper, aluminum phosphate, coating, antibacterial