Zinc anode

Fig. 3. Evans-diagram for the cementation of Cu2+ and Pb2 with zinc amalgam of different zinc content. If the zinc concentration in the mercury employed for this special extraction technique is low, the anodic zinc-dissolution current density may be diffusion controlled and below the limiting cathodic current density for the copper reduction. The resulting mixed potential will lie near the halfwave potential for the reaction Cu2+ + 2e j Cu°(Hg) and only Cu2 ions are cemented into the mercury.

A tridentate SNO ligand coordinates with a bipyridine to give ((2,2 -bipyridine)[2-(2-mercapto-phenyl)iminophenoxy])zinc. The monomeric complex has a distorted trigonal bipyramidal geometry with a phenolate and a thiolate coordinated. The synthesis was carried out electrochemically from anodic zinc in the presence of a disulfide-linked ligand precursor.867... 

Zinc also may be produced by electrolysis of zinc sulfate solution. The zinc oxide in the roasted concentrate is leached with sulfuric acid. The oxide is converted to soluble zinc sulfate. Impurity metals, such as iron, copper, cadmium, arsenic, tin, and cobalt are removed by precipitation, floe formation, and other methods. The purified zinc sulfate solution is electrolyzed using aluminum cathodes and lead anodes. Zinc is deposited on the cathode. 

There is an interesting preparative feature in the chemistry of these compounds the electrochemical oxidation of anodic zinc or cadmium in acetonitrile solutions containing RSH or R2S2 provides an excellent route to the polymeric M(SR)2 compounds 818 this is in contrast to the behaviour when Et3N is also present in the solution, when the isolated product is the... 

Connect the anode (zinc rod) to the positive pole of the power supply and the cathode (nickel foam) to the negative pole of the power supply, set the current intensity at 200 mA for 7 h 40 min (5500 C). 

The presence of strongly electronegative zinc-pigmented coating short circuits all local cell activity on steel. The steel becomes totally cathodic to the anodic zinc coating. The zinc corrodes, but the steel will not corrode even at bare spots, it is mandatory that the zinc coating be in electrical contact with the steel surface therefore, the steel must be stropped of all contamination. 

Galvanized steel is a common example of galvanic coupling where steel (Fe), with a standard electrode potential of —0.440 V vs. SHE, is cathodicaUy protected by zinc, which has a more active standard electrode potential of —0.763 V. Obviously, zinc is not a corrosion-resistant metal and cannot be classified as a barrier coating. It protects steel from corrosion through its sacrificial properties. Because zinc is less noble than iron in terms of the standard electrode potentials, it acts as an anode. The sacrificial anode (zinc) is continuously consumed by anodic dissolution reaction and protects the underlying metal (iron in steel) from corrosion. In practice, sacrificial anodes are comprised of zinc, magnesium alloys, or aluminum. 

K. Koike, H. Watanabe, N. Masuko, "Energy Savings in Zinc Electiowinning with Modification of Lead Anode", Zinc and Lead 95. ibid, 373-383. 

K. Koike, H. Watanabe and N. Masuko, Energy Saving in Zinc Electrowinning with Modification of Lead Anode, Zinc Lead 95. T. Azakami, N. Masuko, J.E. Dutrizac and E. Ozberk, Eds., The Mining and Materials Processing Institute of Japan, Tokyo, Japan, 1995, 373-383. 

The limUing factors for SACP are the electrical resistance of the concrete and the performance of the anode. Zinc will produce about 1 V electromotive force (emf) when coupled to steel If the resistance of the concrete and the anode to concrete interface can be kept lo v this will generate sufficient current to protect the steeL If anode corrosion products, drying out of the concrete or chemical changes increase resistance or decrease the emf, the steel will no longer be protected. The more active the initial corrosion potential of the steel, the smaller the driving voltage. 

American Zinc Institute. (1951). Zinc as a Galvanic Anode, 39 pp. with supplement (1953) Cathodic Protection with Zinc Anodes. Zinc Institute. New York, 49 pp. 

Chung SC, Cheng JR, Chiou SD, Shih HC (2000) EIS behavior of anodized zinc in chloride environments. Corros Sci 42 1249-1268. doi 10.1016/S0010-938X(99)00129-8... 

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