Zinc Oxidation and Redeposition Processes in Aqueous Alkali and Carbonate Solutions: II . Distinction Between Dissolution and Oxide Film Formation Processes

Abstract

The early stages of the process of anodic zinc oxidation in CO32-, SO42-, and C1-solutions around pH 11.5, were studied by cyclic voltammetry, as in part I. Unusual peak current dependence on sweep rate is observed at the first anodic peak (As). This behavior is explained in terms of a mixed process involving coupled diffusion and film formation. By correlating the shapes of peaks and peak potentials for different Zn surface preparations, and the relation of the peak current to sweep rate and to electrode rotation rate, r, the roles of film formation and diffusion of solution species are distinguished. A new method of plotting out cyclic voltammetry peak currents, i,, as a function of sweep rate, s, is proposed that treats the anodic currents in terms of parallel components for dissolution into solution, with diffusion (proportional to sl/2), and for film formation or reduction (proportional to s). This allows a separation of diffusion-controlled and film formation currents to be made. The RDE experiments yield i, = A + Br '/2 and sweep rate experiments showed iD = k,s + k2s '/2 relations apply to the i, for the A, peak. Two processes therefore take place: diffusion-controlled dissolution and direct film formation. The importance of studies at single-crystal surfaces is stressed where resolution of the various processes involved is much clearer. Thus, it is shown that only the direct oxide film formation process is predominant at the single-crystal Zn (0001) face. This compact film is responsible for passivation. The results enable a model for dissolution and coupled-film formation, associated with passivation, at the Zn electrode, to be suggested. The participation 6f these two types of process depends on pH and the types of ions present. ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 155.69.4.4 Downloaded on 2015-06-21 to IP Vol. 134, No. 4 ZINC OXIDATION AND REDEPOSITION PROCESSES II ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 155.69.4.4 Downloaded on 2015-06-21 to IP

Corrosion Inhibition of Zinc by Aqueous Vanadate Species

“…Although identification of these species is complex, these presumably arise from the reduction of two distinct Zn 2+ surface species. [26][27][28] Identical scans in which the only change was the removal of the 5000 s hold displayed only the peak at ∼-1.4 V SCE . Therefore, it is assumed that the peak at ∼-1.2 V SCE arose from a Zn 2+ surface species generated during the holding period.…”

Catechin antioxidant action at various pH studied by cyclic voltammetry and PM3 semi-empirical calculations

“…5(a) and (b). The obtained linear dependence between j pa v À1/2 and v 1/2 , with the intercept on the y-axis, suggests a mixed adsorption-diffusion control, i.e., j pa = k 1 v 1/2 + k 2 v [33]. The constant, k 1 was found to depend linearly on the concentration (k 1 (lA cm À2 V À1/2 s 1/2 ) = À0.08 + 1.27 · c, r 2 = 0.985), as expected from the Randles-Sevcik equation, and the appending diffusion coefficient D = 2.78 · 10 À6 cm 2 s À1 .…”

Electrochemical Behaviors of Zn Anode in Carbonate-based Aqueous Solutions

“…[9][10][11] As shown in Fig. 1(b), two strong anodic current peaks were observed when the concentration of K 2 CO 3 was higher than 4.0 M, while the extent of anodic oxidation of Zn in 0.5-3.0 M K 2 CO 3 aqueous solutions were quite small.…”

“…3,6 There are few papers found that deals with the electrochemistry of Zn in carbonate aqueous electrolyte solutions. [9][10][11] Among them, redox behavior of Zn in concentrated carbonate system have not been reported. In this paper, Zn electrode behaviors in carbonate-based aqueous solutions (the aqueous solutions of K 2 CO 3 and concentrated K 2 CO 3 containing KOH) were examined.…”