PASSIVATION POTENTIAL OF 65/35 ELECTRODEPOSITED SN-NI ALLOY

Electrodeposited Sn-pNi alloy exhibits extremely stable passivity over the whole range of pH. The protective film can exist in several oxidation states, reflected by potentials taken up in solution. A previous estimate put the passivation potential (Flade potential) at ca. - 0·3 V (pH = 0). From the results of potential recovery measurements from low potentials, this is more accurately put at - 0·42 V, and primary passivation seems complete in < 0·5 s. The alloy's behaviour has been explored in solutions of lower concentration of dissolved oxygen than previously achieved and in all solutions, including chlorides, passivity is unimpaired. Additional evidence of the low Flade potential has been obtained from the alloy's behaviour as a cathode under potentiostatic conditions a technique believed new. The sensitivity of tin-nickel electrodes to dissolved oxygen of very low concentrations (po2 < 10-5 atm) suggests that it may have useful analytical applications for oxygen detection. © 1968 Pergamon Press.