Zinc Electrocrystallization from Impurity‐Containing Sulfate Baths

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Abstract
In the present paper the behavior of various impurities (Ni, Co, Cu, Cd, Sb, Ge, As, Bi), added to acid sulfuric baths, has been examined by means of chemical analysis of the zinc deposits, current efficiency measurements, and scanning electron microscope observations of the cathodic surface. The effect of gum arabic additions to the electrolyte has also been considered. Only antimony, germanium, and arsenic attain a limiting current of codeposition with zinc as a consequence of stibine, arsine, and germane evolution. The other impurities do not reach limiting current conditions. All the impurities considered induce, in high acidity baths, instabilities in the electrochemical system, which appears to oscillate between two nonsteady states. SEM observations showed that the impurities always alter the deposit morphology, changing completely, in some cases, the morphological pattern with respect to pure zinc.
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