Anodic Oxide Films on Nickel in Acid Solutions

The formation and removal of steady‐state oxide films on nickel elecrodes anodized in solutions of p H 8.4–2.0 have been examined. Surface activity measurements showed that complete removal of all of these oxide films was possible in solutions of with moderate cathodic treatments. Instability of the p H in the vicinity of the electrode was the probable cause of oxide nonreducibility at . The oxide was removed cathodically by a galvanostatic charging technique in p H 2.8 and a relative measure of the amount of oxide remaining at any time during the cathodic pulse could be obtained by subsequent application of an anodic potential step. No significant chemical dissolution of the oxide occurred during cathodic charging, in contrast to the situation on open circuit. However, the quantity of oxide on anodized nickel could not be determined from the total cathodic charge passed in its removal because of simultaneous massive hydrogen evolution. This was not the case with the oxide on electropolished nickel where galvanostatic charging techniques could be used to accurately determine the oxide thickness.