Zinc iron oxide electrodes

The voltammograms for marmatite electrode in different pH buffer solutions are presented in Fig. 4.22. It can be seen from Fig. 4.22(a) that the first anodic peak occurred at about 200 mV, which may be due to the oxidation of dithiocarbamate to disulphide. The anodic oxidation peaks at higher potential may be attributed to the further oxidation of marmatite to form oxy-sulphur and zinc/iron hydroxide resulting in flotation descending. 

Zinc and zinc-coated products corrode rapidly in moisture present in the atmosphere. The corrosion process and its mechanism were studied in different media, nitrate [283], perchlorate [259], chloride ions [284], and in simulated acid rain [285]. This process was also investigated in alkaline solutions with various iron oxides or iron hydroxides [286] and in sulfuric acid with oxygen and Fe(III) ions [287]. In the solution with benzothia-zole (BTAH) [287], the protective layer of BTAH that formed on the electrode surface inhibited the Zn corrosion. 

Carbon Dioxide. As the debate of the effect of greenhouse gases rages on, the simple fact remains that carbon dioxide production is one of the known side reactions of most metal-production operations. Carbon is an effective metal reductant. Coke is used to produce pig iron from iron oxide ores and lead from sulfide ores in blast furnaces, carbon electrodes are used to produce aluminum from bauxite leaching products, and coal is used in the reduction of zinc oxide in retorting furnaces. All told, the resulting product of metal reduction is the oxidation of carbon to carbon dioxide. It is important to keep in mind that the production of carbon dioxide has been reduced dramatically since the start of the Industrial Revolution of the late nineteenth-century. This is best exemplified by the history of steel making in the world. 

Zinc is used as the negative electrode material in aqueous primary cells because it has a high energy density. However, Zn is prone to corrosion, particularly when certain impurities are present, that can result in decreased battery life and compromised performance. A common contaminant is iron. When it comes into contact with the Zn and becomes galvanically coupled with it, hydrogen gas (H2) will form at the iron surface from the reduction of water in the electrolyte. Zinc is oxidized and dissolves into the electrolyte as zincate or precipitates as ZnO. 

We have investigated copper preparations (Raney s and others), Raney nickel, zinc oxide, iron oxide, vanadium quin-toxide (VjOg), silica gel (SiOj) and some varieties of silicon dioxide applied as carriers, zinc ferrocyanide pure, and with Fe + and Cu + ions, a cobalt-thorium contact for Fischer and Tropsch s s5mthesis, zinc hydroxide with Co + ions, and silica gel with nickel sulphate (II) fixed on it. We have investigated contact fixed on a carrier and without a carrier, with additions of an activator, etc. For example, Co + ions on Zn(0H)2 could be clearly detected potentiometrically and still in the quantity of 3.10 g Co + to a powder electrode. 

In acidic electrolytes only lead, because it forms passive layers on the active surfaces, has proven sufficiently chemically stable to produce durable storage batteries. In contrast, in alkaline medium there are several substances basically suitable as electrode materials nickel hydroxide, silver oxide, and manganese dioxide as positive active materials may be combined with zinc, cadmium, iron, or metal hydrides. In each case potassium hydroxide is the electrolyte, at a concentration — depending on battery systems and application — in the range of 1.15 - 1,45 gem"3. Several elec-... 

Thus films can be divided into two groups according to their morphology. Discontinuous films are porous, have a low resistance and are formed at potentials close to the equilibrium potential of the corresponding electrode of the second kind. They often have substantial thickness (up to 1 mm). Films of this kind include halide films on copper, silver, lead and mercury, sulphate films on lead, iron and nickel oxide films on cadmium, zinc and magnesium, etc. Because of their low resistance and the reversible electrode reactions of their formation and dissolution, these films are often very important for electrode systems in storage batteries. 

This reduction step can be readily observed at a mercury electrode in an aprotic solvent or even in aqueous medium at an electrode covered with a suitable surfactant. However, in the absence of a surface-active substance, nitrobenzene is reduced in aqueous media in a four-electron wave, as the first step (Eq. 5.9.3) is followed by fast electrochemical and chemical reactions yielding phenylhydroxylamine. At even more negative potentials phenylhydroxylamine is further reduced to aniline. The same process occurs at lead and zinc electrodes, where phenylhydroxylamine can even be oxidized to yield nitrobenzene again. At electrodes such as platinum, nickel or iron, where chemisorption bonds can be formed with the products of the... 

The nickel-based systems include the flowing systems nickel—iron (Ni/Fe), nickel—cadmium (NiCd), nickel—metal hydrides (NiMH), nickel—hydrogen (Ni/ H2), and nickel—zinc (Ni/Zn). All nickel systems are based on the use of a nickel oxide active material (undergoing one valence change from charge to discharge or vice versa). The electrodes can be pocket type, sintered type, fibrous type, foam type, pasted type, or plastic roll-bonded type. All systems use an alkaline electrolyte, KOH. 

Electrorefining can be used to purify a metal by using alternate electrodes of a pure and impure metal. Impurities oxidized at the anode, which is made of the impure metal, travel into solution. By arranging the cell appropriately, the ion of the metal to be purified is reduced on the pure metal cathode. For example, copper metal that contains lead and iron may be used as one electrode and pure copper as the other electrode in a cell. When the proper voltage is applied, copper, lead, and zinc will be oxidized and move into the electrolyte. Because copper is more easily reduced compared to zinc and lead, it will be plated out at the pure copper cathode. Therefore, this process effectively removes the zinc and lead impurities from the copper. 

The electrochemical oxidation of tyramine in NaOH/MeOH media gives films of polytyramine (25). The film, on a platinum electrode, can complex copper(II) ions from aqueous media and cobalt(II), iron(II), manganese(II) and zinc(II) from organic media. X-ray photoelectron spectroscopy established that coordination of the metal ions had occurred. For cobalt, evidence of coordination to both ether and amine functions is obtained, but for the other metal ions evidence of ether coordination is less definitive. 

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