The Effect of Several Electrode and Electrolyte Additives on the Corrosion and Polarization Behavior of the Alkaline Zinc Electrode

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Abstract
The corrosion behavior of zinc in at 25° C was investigated through measurement of the rate of hydrogen evolution at the corrosion potential. Anodic and cathodic potentiostatic polarization curves as a function of alloying and additions to the electrolyte were obtained. It was found that the corrosion and polarization behavior of 99.999% zinc can be explained by mixed‐potential theory assuming that the reactions were . Good agreement between theoretical curves obtained by computer solution of the kinetic equations corresponding to the above reactions and actual polarization measurements was obtained in the absence and presence of zincate. Theoretical and experimental corrosion rates also agreed well. Binary alloys [0.2–1.0 w/o (weight per cent)] and alloys (0.2–0.8 w/o) made up from high‐purity metals had values which were lower than those for zinc, while values of commercial zinc alloys were much higher than those of zinc, most likely due to the presence of low overvoltage impurities such as Cu, Ni, or Fe. Addition of 10−3M copper, tin, or lead ions to the electrolyte also influenced , which in the presence of metal ions noble to zinc is no longer equivalent to the corrosion rate. The strong increase of in the presence of Cu ions is explained by the low hydrogen overvoltage of Cu, while the decrease of in the presence of Pb ions is explained by the high hydrogen overvoltage of Pb. Anions such as Cl− or Br− do not affect . In the presence of thiourea, increases steadily, while S2− leads to severe corrosion.

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