Corrosion of Sn–Co alloy in alkaline media and the effect of Cly and Bry ions

Sn–Co electrodeposits alloy of approximate composition 80% Sn–20% Co wt%.can be obtained from a gluconate bath as single phase CoSn2, which is similar in appearance to decorative chromium. The potentiodynamic and cyclic voltammogram techniques were used to study the corrosion behaviour of CoSn2in sodium borate solutions Na2B4O7.at pHs9.6. The effect of different factors such as concentration of borate ions, pH, potential scan rate, successive cyclic voltammetry, and progressive addition of halide ions Clyand Bry. on the electrochemical behaviour of CoSn2 alloys are discussed. The observed corrosion resistance of electrodeposited CoSn2 alloy is due to the formation of a thin passive film, which is examined by X-ray spectroscopy and believed to be mainly tin and cobalt oxides. The voltammograms involve four anodic peaks, the first and second of which correspond to the formation of SnO and SnO2 and the third and fourth related to the formation of cobalt oxides. SEM examination confirms that pitting corrosion takes place in presence of borax and is increased by adding halide ions. q1999 Elsevier Science B.V. All rights reserved