Dissolution Current and Pitting Potential of Zinc in KOH Solutions in Relation to the Concentration of Aggressive Ions
1976; Taylor & Francis; Volume: 11; Issue: 4 Linguagem: Inglês
10.1179/000705976798319900
ISSN2048-2892
Autores Tópico(s)Electrochemical Analysis and Applications
ResumoPotentiodynamic anodic polarisation curves for zinc were obtained in dilute (10−3 M) solutions of KOH that favoured metal dissolution with only a slight tendency to passivate the zinc, and in more concentrated (10−2 M) solutions that favoured passivation of the zinc. Addition of aggressive halide ions (Cl−, Br−, I−) to the 10−3 M solution caused a shift of the dissolution potential to more negative values and a marked increase in corrosion rate, suggesting adsorption of the anions on to the bare metal surface. The difference between the dissolution current density, io, in 10−3 M KOH alone, and in the presence of halide ions, iagg, was given by: log (iagg−io) = a + b log Cagg, where a and b are constants.In 10−2 M KOH, small additions (2 × 10−4 M) of aggressive ions did not affect the dissolution kinetics. At higher concentrations the c.d. increased sharply at a well defined potential, or pitting potential, Ep, given by the relation: Ep = α − β log Cagg, α and β being constants. It is assumed that in 10−2 M KOH the aggressive anion acts by penetrating the oxide, or by becoming incorporated in it as an impurity, altering its physical and electrical properties.
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