Electrochemical corrosion behavior of a novel antibacterial stainless steel Yongqian Liu a , Jibiao Li b , Emeka E. Oguzie b,c , Ying Li b , Demin Chen a , Ke Yang a , Fuhui Wang b, * a Center for Engineering Materials, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Rd., Shenyang 110016, China b State Key Laboratory for Corrosion and Protection, Institute of Metal Research, Chinese Academy of Sciences, 62 Wencui Rd., Shenyang 110015, China c Electrochemistry and Materials Science Research Laboratory, Department of Chemistry, Federal University of Technology Owerri, PMB 1526, Owerri, Nigeria article info Article history: Received 6 October 2008 Accepted 4 March 2009 Available online 19 March 2009 Keywords: A. Stainless steel A. Copper B. EIS B. Polarization C. Corrosion abstract A novel antibacterial stainless steel (ASS) with martenstic microstructure has been recently developed, by controlled copper ion implantation, as a new functional material having broad-spectrum antibacterial properties. The electrochemical corrosion behavior of the ASS in 0.05 mol/L NaCl was assessed using lin- ear polarization and electrochemical impedance spectroscopy (EIS) and compared with that of a conven- tional stainless steel (SS) without copper ion implantation. The ASS exhibited higher corrosion susceptibility in the chloride medium; with a more negative (active) corrosion potential, higher anodic current density and lower charge transfer and polarization resistance. This has been attributed to the occurrence of copper-catalyzed interfacial reactions. A functional tool, 3-D presentation of EIS data, has been employed in analyzing the electrochemical corrosion processes as well as probing complex interfacial phenomena. Ó 2009 Published by Elsevier Ltd. 1. Introduction Copper, incorporated in some stainless steels, has been reported to impart antimicrobial activity by releasing copper ions, which have a devastating effect on bacterial cells. This has formed the ba- sis for design of some copper-containing antibacterial stainless steels (ASS) [1,2]. Such antimicrobial stainless steels find wide- spread utility in medical appliances and food processing to ensure improved safety and hygiene. Baena et al. [3] demonstrated that an ASS containing copper (3.8%) and niobium (0.1%) exhibited excel- lent antimicrobial properties due to niobium-stimulated copper precipitation. Yang et al. [4] reported that a ferritic ASS (1.5 wt% Cu) was about 99% potent in eliminating Staphylococcus and Coliform bacteria. The effectiveness of any antibacterial treatment depends strongly on factors such as the nature and conditions of treatment as well as the resulting ASS microstructure, amount of antibacterial additive and the amount of antimicrobial additive that precipitates on the protective oxide film. Copper as an alloying element has been used to improve the uniform corrosion resistance of some stainless steels in a number of environments [5,6], although its effect on localized corrosion in chloride media is neither uniform nor definite. For instance, Cu has been reported to exert both harmful [7] and beneficial [7,8] effects on the corrosion rate and pitting potential of austenitic stainless steels in chloride environments. Ujiro et al. [7] observed that alloying Cu had a harmful effect on the localized corrosion resistance of both austenitic and ferritic stainless steels in the noble potential range. Such detrimental effect of Cu poses signifi- cant challenges in the design and fabrication of copper ion-con- taining ASS. Long-lasting, broad-spectrum antibacterial efficacy must necessarily be balanced by good corrosion resistance. In any situation, an optimal Cu content exists beyond which corrosion resistance is compromised. According to Hong and Koo [9] the Cu content of SUS 304 austenitic stainless steel should not exceed 3.5% to ensure balance between corrosion resistance and antimi- crobial activity. In previous reports [10,11] we had produced ASS with marte- nistic microstructure, maintaining effective, long-lasting and broad-spectrum antibacterial properties. Nonetheless, electro- chemical behavior of such martenistic ASS was not explored and to our knowledge has not yet been reported. Accordingly, this pa- per presents a comparative study of electrochemical properties of the martenistic ASS and those of a contemporary SS, to provide in- sights into effect of copper on the electrochemical corrosion behav- ior. The applicability of a new tool; 3D presentation of EIS data, for such studies is also highlighted. 2. Experimental Two martenistic stainless steels, with (ASS) and without (SS) copper addition, were used in this study. The nominal chemical compositions (wt%) are listed in Table 1. Before experimental tests, all the materials were annealed for 6 h at 700 °C, followed by rapid cooling. Details of the Cu ion implantation and microstructural characterization of ASS including details of the heat treatment reg- 0010-938X/$ - see front matter Ó 2009 Published by Elsevier Ltd. doi:10.1016/j.corsci.2009.03.007 * Corresponding author. E-mail address: fhwang@imr.ac.cn (F. Wang). Corrosion Science 51 (2009) 1083–1086 Contents lists available at ScienceDirect Corrosion Science journal homepage: www.elsevier.com/locate/corsci