Ni-free alloys as final coatings: white bronze coatings on copper

The problem of allergies arising from the presence of Ni in alloys used for decorative objects coming into contact with the skin has become increasing ly important over the past five to ten years. As an alternative, "white bro nze" has been shown to be an effective solution even from an aesthetic poin t of view. This work investigates the corrosion behaviour of copper treated with two different techniques: electroplating and ion beam mixing. To this end copper has been electroplated with a thin (0.3 and 0.04 mum) coating o f white bronze (Cu 66, Sn 23, Zn 10, Pb 1 wt%), the high brightness (as a n oble metal) and corrosion resistance of which allow it to be used in decora tive industries for jewellery, watches, etc. The bronze coating was ion bea m mixed through bombardment with an argon ion beam. The corrosion behaviour of the bronze coatings was compared with that of pure copper through two m ethod of analysis: a) electrochemical analysis, aimed at measuring the corr osion rate in a alkaline solution (pH = 12.4); and b) surface analysis inte nded to verify the thickness, homogeneity and composition of coatings throu gh Rutherford backscattering spectroscopy (RBS) and scanning electron micro scopy (SEM). The implanted bronze electroplated copper showed the best corr osion behaviour. Electrochemical tests showed low corrosion rates and a cor rosion mechanism similar to that of more noble coatings.