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The Influence of Halide Anions on the Anodic Behavior of Nickel in Borate Solutions
Author(s) -
Abd El Aal E. E.,
Abd El Haleem S. M.
Publication year - 2005
Publication title -
chemical engineering and technology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.403
H-Index - 81
eISSN - 1521-4125
pISSN - 0930-7516
DOI - 10.1002/ceat.200500146
Subject(s) - halide , nickel , inorganic chemistry , chemistry , anode , molybdate , tungstate , chromate conversion coating , corrosion , pitting corrosion , bromide , electrode , organic chemistry
The anodic behavior of nickel in Na 2 B 4 O 7 solutions containing various concentrations of NaCl, NaBr, or NaI as pitting corrosion agents was studied using the potentiodynamic technique. In absence of the halide anions, the E/i curves exhibit active and passive regions prior to oxygen evolution. The passivity is due to the formation of nickel oxides on the electrode surface. The presence of low concentrations of the halide anions has no effect on the mechanism of nickel passivity. High aggressive anion concentrations stimulate the active region and tend to break down the passive film, leading to pitting corrosion. The susceptibility of the nickel anode to pitting corrosion is enhanced with increasing halide anion concentration and is decreased with increasing pH of solution. The aggressiveness of the halide anions towards the stability of the passive film decreases in the order: Cl – > Br – > I – . The addition of increasing concentrations of tungstate, chromate, or molybdate anions causes a shift of the breakdown potential in the noble direction, indicating the inhibitive action of the added anions. The inhibiting tendency of these anions decreases in the order: WO 4 2– > CrO 4 2– > MoO 4 2– .