Passivation of zinc in aqueous solutions of Cr(VI) as function of pH.

The electrochemical behavior of zinc in Cr(VI) aqueous solutions was studied as function of pH measuring the variation of the open circuit potential with time and by linear potential sweep voltammetry. Under open circuit, at pH 8.4 there is a building up of a zinc hydroxide film which can contain Cr2O3. As the solution becomes more acidic, the relative amount of the ZnO/Zn(OH)(2) and Cr2O3 mixture, which constitute the film, changes and, at pH 1.8, the film is basically formed by Cr2O3 and ZnO. The polarization curves put in evidence the observed trend under open circuit conditions.