Corrosion zinc electrode

The rotating hemisphere electrode has been used to investigate the effect of AC on the electrodissolution and deposition reactions of zinc in zinc chloride [25] and copper in acid copper sulfate solutions [55], AC was found to increase the rate of nucleation and produce more uniform deposit on the zinc electrode. The corrosion of an iron rotating hemisphere in dilute sulfuric acid was investigated by Haili [31] using the AC impedance measurement. 

Zhu etal. [219] have also investigated the influence of surfactants on the electrochemical behavior of zinc electrodes in alkaline solutions. In the presence of surfactants, the dendrite growth is reduced and the zinc deposit is more uniform and compact. Therefore, perfluorosurfactants can be used for decreasing the corrosion of zinc batteries. 

A great research interest concerns zinc corrosion inhibition. Chromate solutions were used [289-293] for the inhibition of zinc corrosion. The surface film contained a mixture of zinc oxide and hydroxide of chromium(III). Different behaviors of the passivated zinc electrode was observed depending on the cation of the used chromate [293]. 

The corrosion behavior of zinc-coated steel electrodes electrochemically modified by polypyrrole [311] and zinc electrode in solution containing reducing polymer (Polyox WSR-301) [312] was investigated. 

Zinc electrodes are sometimes used as references in marine environments. In sea water (pH = 8) the rate of corrosion is at a minimum and the presence of chloride ions ensures the continuous dissolution of the zinc surface (ZnCl2 is soluble). This process provides a potential, which is stable within 20mV [15], Their use in concrete (alkaline solution, pH = 13) is questionable, and not recommended. At pH about 12.5, zinc reacts rapidly to form soluble zincates and hydrogen gas is liberated [16] ... 

The corrosion of zinc electrode in zinc cells and batteries contributes to self-discharge,... 

The actual cell voltage is about 1.5 V, it does not depend on the actual pH-value of the electrolyte solution as obvious from the absence of protons and hydroxide ions in the cell reaction equation. It slightly depends on the source of the used manganese dioxide. Initially naturally occurring manganese dioxide was used. The battery required a quality of less than 0.5% copper, nickel, cobalt, and arsenic to avoid undue corrosion of the zinc electrode. Currently synthetic manganese dioxide is prepared either by chemical (CMD) or electrochemical (EMD) procedures. For improved electrical conductivity graphite or acetylene black are added. Upon deep... 

Corrosion of zinc was initially prevented by amalgamation of the zinc electrode (i.e., by adding soluble mercury salts which result in a mercury deposit by -> cementation). Currently organic additives are used for corrosion prevention. 

To discuss the corrosion of metals in acid solution, we consider the cell shown in Fig. 34.11(a). It consists of a zinc electrode and a hydrogen electrode immersed in a ZnS04 solution that contains sufficient sulfuric acid to prevent the precipitation of Zn(OH)2. If this cell is short-circuited, the reaction... 

Upon polarization of either electrode, the cell potential moves along the oxidation and reduction curves as shown in Fig. 1.1. When the current through the cell is f, the potential of the copper and zinc electrodes is Cj cu and e zn > and each of the electrodes have been polarized by (Ceq.cu i.Cu) and (Ceq.zn i,z )- Upon further polarization, the anodic and cathodic curves intersect at a point where the external current is maximized. The measured output potential in a corroding system, often termed the mixed potential or the corrosion potential (Tcorr)> h the potential at the intersection of the anodic and the cathodic polarization curves. The value of the current at the corrosion potential is termed the corrosion current (Icon) and can be used to calculate corrosion rate. The corrosion current and the corrosion potential can be estimated from the kinetics of the individual redox reactions such as standard electrode potentials and exchange current densities for a specific system. Electrochemical kinetics of corrosion and solved case studies are discussed in Chapter 3. 

The concept of polarization in a corrosion cell can be explained by considering a simple galvanic cell, such as a Daniel cell, with copper and zinc electrodes. The Evans diagram of a Daniel cell shown in Fig. 3.5 is the basis for understanding the underlying corrosion process kinetics [26,27]. 

Figure 16.10 OCP curves of coated PPy zinc electrodes cured In air for 1 h at 180 °C and immersed in 3.5% NaCI solution. PPy films (Ri2iim thick) were synthesized in 2 M NaSac+ 0.5 M Py at pH 5 and 1.9 M NaSac + 0.1 M DISacH + 0.5 M Py at pH 5.4. (Reprinted with permission from Chemistry of Materials, Ultrafast electrosynthesis of high hydrophobic polypyrrole coatings on a Zinc electrode Applications to the protection against Corrosion by E. Hermelin,]. Petitjean, P.C. Lacaze et al., 20, 13, 4447—4456. Copyright (2008) Elsevier Ltd)...

E. Hermelin, J. Petitjean, J.-C. Lacroix, K.I. Chane-Ching, J. Tanguy, and P.C. Lacaze, Ultrafast electrosynthesis of high hydrophobic polypyrrole coatings on a Zinc electrode Applications to the protection against Corrosion, Chem. Mater., 20, 4447 1456 (2008). 

The second battery (Fig. 10.17) is a series of six cells with bipolar (or duplex) electrodes. Each cell has the same components as the first cell, i.e. zinc can, separator, positive paste and carbon current collector. The latter is not a carbon rod but the bottom face of the duplex electrode. The whole set of cells is sealed in wax. In both cells the zinc electrode rapidly develops porosity as the corrosion process occurs while the performance is largely determined by the quality of... 

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