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Electrochemical behaviour of nickel anode in H 2 SO 4 solutions and the effect of halide ions
Author(s) -
Abd El Rehim S. S.,
Abd El Wahaab S. M.,
Abdel Maguid E. A.
Publication year - 1986
Publication title -
materials and corrosion
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.487
H-Index - 55
eISSN - 1521-4176
pISSN - 0947-5117
DOI - 10.1002/maco.19860371006
Subject(s) - dissolution , halide , passivation , nickel , electrochemistry , cyclic voltammetry , inorganic chemistry , anode , chemistry , ion , oxide , halogen , analytical chemistry (journal) , electrode , organic chemistry , alkyl , layer (electronics)
The electrochemical behaviour of pure nickel in H 2 SO 4 solutions has been potentiodynamically investigated. The effects of the following factors on the anodic dissolution and passivation of the metal are discussed: potential scan rate, successive cyclic voltammetry and progressive additions of Cl − , Br − and I − ions. Increasing the potential scan rate increases the critical current density i cc , denoting that the active dissolution of nickel in H 2 SO 4 is a diffusion controlled process. Cyclic voltammetry shows that the reverse excursion does not restore the anode to its active state. On successive cycling, the height of i cc decreases; this could be attributed to the decrease in the reduction efficiency of passivating oxide film during the cathodic half cycles. The presence of the halogen ions below a certain concentration specific to each anion inhibits the anodic dissolution both in the active and passive states. The inhibitive action of these additives decreases in the order I − , Br − , Cl − . Beyond the specific concentrations, the halogen ions accelerate the anodic dissolution and shift the active passive transition to more positive values. The aggressiveness of these anions decreases in the sequence Cl − , Br − , I − , Further increase in the halogen ion concentrations can lead to breakdown of the passive film and initiate pitting. The susceptibility of nickel to pitting attack enhances with increasing H 2 SO 4 concentration.