Metal ion release and surface composition of the Cu–18Ni–20Zn nickel–silver during 30 days immersion in artificial sweat

In order to study nickel ion release associated with nickel allergy, Cu–18Ni–20Zn nickel–silver alloy was immersed in artificial sweat and Ringer physiological solution for 30 days. Dissolution of metal ions was measured as a function of time, and the characteristics of the solid surface layer formed after 30 days were studied by SEM/EDS and XPS. The dissolution of nickel prevails over dissolution of copper and zinc. Nickel release in artificial sweat is approximately 10 times higher than in Ringer physiological solution and in both solutions the nickel release exceeds 0.5 μg cm−2 week−1, the threshold above which the allergy is triggered. Evidence of selective nickel dissolution is reported. The composition of the surface layer formed in artificial sweat and in Ringer physiological solution differs in the content of nickel and chlorine. In artificial sweat, the major constituents of the surface layer are dominantly oxides, Cu2O and ZnO, with traces of chlorine. In Ringer physiological solution, the composition of the surface layer changes to a mixture of oxides, chlorides and/or oxychlorides. Two components peaks were detected in the Cl 2p3/2 peak; however, it was not possible to distinguish the exact nature of the chloride compound formed. The mechanism of nickel release is discussed as a function of the composition of the solution.