Electrochemical Studies of Plasma-formed Films of Tin

The electrochemical behavior of plasma-formed tin films on aluminum is compared with that of conventional β-Sn. Rest potential measurements in K 2SO 4 solutions (pH 3.4-5.9) show that plasma-formed tin samples attain more noble potentials than those of pure tin for experimental times up to 4 h duration. The plasma-formed tin exhibits a similar behavior to conventional β-Sn when cathodically polarized in 0.33 M citric acid. However, a passive film apparently forms on the surface during the anodic polarization whereas the pure tin shows a behavior exemplifying active metal dissolution. Auger analyses show an increase in the [O]/[Sn] ratio for both pure and plasma-formed tin after oxidation but the value for plasma-formed tin is higher. Atomic absorption analyses show that more plasma-formed tin dissolves into solution than predicted by Faraday\u27s law. This suggests that considerable local corrosion occurs on the plasma-formed tin surface. However, the total corrosion current is almost ten times less than that for pure tin. The unique physical or chemical nature (carbon and oxygen in the film, fine grain size and low porosity) of plasma-formed tin is believed to play an important role in its electrochemical behavior. © 1985