Studies on Tribocorrosion Explain Low Nickel Release From Euro Coins

摘要

Patch tests of 1-and 2-euro coins to the skin has shown to induce eczematous reactions,being more frequent and intense in comparison with those provoked by other coins.Handling experiments have however not indicated any risk of nickel release from euro coins.Nickel release is facilitated by corrosion of the coinage metal and is as such influenced by humidity,temperature and sweat composition.Furthermore it is known that combined corrosion and wear (tribocorrosion) can cause a synergy effect accelerating material degradation.The objective of this study is to investigate the effect of friction during handling,on the nickel release from euro coinage alloys.Electrochemical tests and tribocorrosion tests have been performed.The results surprisingly show a decrease in anodic current when combining corrosion and wear.A possible explanation for this finding is a change in transport kinetics and the formation of a passivating layer of atacamite CuCl2-3Cu(OH)2 and malachite CuCO3-Cu(OH)2 smeared onto the surface by the mechanical rubbing with washable leather during the wear test.