Taiwan is an island with a humid subtropical climate. The relatively warm seawater results in biofouling of the surfaces of marine facilities. Biocide application is a common practice for combating and eliminating adhesive fouling. However, a single type of biocide may have limited antimicrobial effects due to the relatively high microbial diversity in marine environments. Therefore, applying a mixture of various biocides may be necessary. In this study, the antimicrobial and anticorrosion properties of a newly designed composite biocide, namely a combination of thymol and benzyldimethyldodecylammonium chloride, were investigated by applying the biocide to 304 stainless steel substrates immersed in inocula containing bacterial strains from Tamsui and Zuoying harbors. The ability of 3TB and 5TB treatments to prevent sessile cells and biofilm formation on the 304 stainless steel coupon surface was determined through scanning electron microscopy investigation. In addition, confocal laser scanning microscopy indicated that the 5TB treatment achieved a greater bactericidal effect in both the Tamsui and Zuoying inocula. Moreover, electrochemical impedance spectroscopy revealed that the diameter of the Nyquist semicircle was almost completely unaffected by Tamsui or Zuoying under the 5TB treatment. Through these assessments of antimicrobial activity and corrosion resistance, 5TB treatment was demonstrated to have superior bactericidal activity against mixed strains in both southern and northern Taiwanese marine environments.

Although extensive studies have examined the tribocorrosion behavior of stainless steels, the performance of medium-entropy austenitic super stainless steels (MEASS) under severe combined corrosion and mechanical wear conditions has not been fully established. This study systematically compares the tribocorrosion behavior of a newly developed MEASS with conventional S31254 super austenitic stainless steel (SASS) in a 1 M H₂SO₄ solution, aiming to explore innovative material designs for enhanced performance under these demanding conditions. Electrochemical tests were conducted under both open-circuit potential (OCP) and cathodic potential, with and without sliding wear, to assess the corrosion, wear, and synergistic effects influencing the tribocorrosion performance. Worn surface morphologies and hardness were analyzed using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and hardness measurements, respectively. The experimental results revealed that MEASS exhibits a superior repassivation capability compared to S31254, with a 34.3% lower total material loss after 24 h of tribocorrosion test, primarily attributed to enhanced strain hardening and improved wear resistance. These findings emphasize the strong potential of MEASS for use in corrosive environments, particularly in chemical processing industries, where high resistance to wear and corrosion is critically required.

Regarded as a potential replacement for chromate conversion coating, cerium-based conversion coating system for magnesium alloys has been widely discussed for many years. As revealed in previous research, trivalent cerium conversion coating formed in aqueous solution is found to have a loose structure with a fibrous layer on the top, which leads to a limited barrier protection. To enhance the corrosion resistance of trivalent cerium conversion coating, some approaches that include non-aqueous system and quadrivalent cerium conversion coating have been investigated. In contrast, an aluminum conversion coating based on aluminum nitrate, which is expected to have a protection effect similar to that of cerium nitrate, has also been proposed. However, the corrosion behavior of aluminum conversion coating and its feasibility of being conducted in non-aqueous solution have not been well studied so far. Hence, this study is focused on a comparative understanding through a combination of electrochemical analysis and microstructural characterization. Prior to conversion coating process, the AZ31 plates were abraded using emery paper up to 2500 grit and rinsed with deionized water. The conversion coating process was conducted in aqueous or ethanol solution for 60 s under room temperature, after which the coated plates were heated by hot air of approximately 75 °C for drying. Gray coatings can be observed after both cerium and aluminum coating processes conducted in aqueous solution. As observed in electrochemical impedance spectroscopy (EIS), cerium conversion coating slightly increases the total impedance from around 5,000 to 7,000 Ωcm² and exhibits a partially blocked electrode behavior, which is coherent with its loose microstructure. However, aluminum conversion coating shows a different behavior with an apparent barrier protection, which strongly elevates the total impedance to over 50,000 Ωcm². As conducted in ethanol solution, the formation of cerium and aluminum conversion coatings are both retarded. Without the existence of citric acid, aluminum conversion coating can still provide certain corrosion protection, while cerium conversion coating can barely formed. With citric acid added, however, cerium conversion coating formed in ethanol solution exhibits an impedance even higher than that of the coating formed in aqueous solution in EIS, while the total impedance of aluminum conversion coating is further decreased.