Cobalt anodes

Many competitive programs to perfect a metallic anode for chlorine arose. In one, Dow Chemical concentrated on a coating based on cobalt oxide rather than precious metal oxides. This technology was patented (9,10) and developed to the semicommercial state, but the operating characteristics of the cobalt oxide coatings proved inferior to those of the platinum-group metal oxide. 

D. L. CaldweU and M. J. Hazeltigg, "Cobalt Spiael-Based Chlorine Anodes," paper presented t dnances in Chlor-A.lkali Technology, London, 1979. 

Good results are obtained with oxide-coated valve metals as anode materials. These electrically conducting ceramic coatings of p-conducting spinel-ferrite (e.g., cobalt, nickel and lithium ferrites) have very low consumption rates. Lithium ferrite has proved particularly effective because it possesses excellent adhesion on titanium and niobium [26]. In addition, doping the perovskite structure with monovalent lithium ions provides good electrical conductivity for anodic reactions. Anodes produced in this way are distributed under the trade name Lida [27]. The consumption rate in seawater is given as 10 g A ar and in fresh water is... 

Fig. 4. Filled graphite polyhedra found in soot produced with an anode containing sulfur and cobalt.

C.-H. Kiang e o/.[33] reported that the singlelayered coiled lubes were obtained by co-vaporizing cobalt with carbon in an arc fullerene generator. A single-layered helical structure with radii of curvature as small as 20 nm was seen. These helically coiled forms lend to bundle together. In the soot obtained with sulfur-containing anodes, they also found the 1.3-nm diameter lube coil around the 3.6 nm tube (see Fig. 14). This kind of structure was theoretically proposed in ref. [14]. 

Holden et al. [27] reported the first Raman results on nanotubes produced from a Co-catalyzed carbon arc. Thread-like material removed from the chamber was encapsulated in a Pyrex ampoule in -500 Torr of He gas for Raman scattering measurements. Sharp first-order lines were observed at 1566 and 1592 cm and second-order lines al 2681 and 3180 cm , but only when cobalt was present in the core of the anode. These sharp lines had not been observed previously in... 

Fig. 10. (a) Raman spectra (T = 300 K) of arc-derived carbons from a dc arc cobalt was absent (dotted line) and cobalt was present (solid line) in the carbon anode, (b) the difference spectrum calculated from (a), emphasbjng the contribution from Co-catalyzed nanolubes, the inset to (b) depicts a Lorentzian fit to the first-order spectrum (after ref. [27]). 

In 1996, consumption in the western world was 14.2 tonnes of rhodium and 3.8 tonnes of iridium. Unquestionably the main uses of rhodium (over 90%) are now catalytic, e.g. for the control of exhaust emissions in the car (automobile) industry and, in the form of phosphine complexes, in hydrogenation and hydroformylation reactions where it is frequently more efficient than the more commonly used cobalt catalysts. Iridium is used in the coating of anodes in chloralkali plant and as a catalyst in the production of acetic acid. It also finds small-scale applications in specialist hard alloys. 

Edwards e/a/. carried out controlled potential, slow strain-rate tests on Zimaloy (a cobalt-chromium-molybdenum implant alloy) in Ringer s solution at 37°C and showed that hydrogen absorption may degrade the mechanical properties of the alloy. Potentials were controlled so that the tensile sample was either cathodic or anodic with respect to the metal s free corrosion potential. Hydrogen was generated on the sample surface when the specimen was cathodic, and dissolution of the sample was encouraged when the sample was anodic. The results of these controlled potential tests showed no susceptibility of this alloy to SCC at anodic potentials. 

Amorphous Fe-3Cr-13P-7C alloys containing 2 at% molybdenum, tungsten or other metallic elements are passivated by anodic polarisation in 1 N HCl at ambient temperature". Chromium addition is also effective in improving the corrosion resistance of amorphous cobalt-metalloid and nickel-metalloid alloys (Fig. 3.67). The combined addition of chromium and molybdenum is further effective. Some amorphous Fe-Cr-Mo-metalloid alloys passivate spontaneously even in 12 N HCl at 60° C. Critical concentrations of chromium and molybdenum necessary for spontaneous passivation of amorphous Fe-Cr-Mo-13P-7C and Fe-Cr-Mo-18C alloys in hydrochloric acids of various concentrations and different temperatures are shown in Fig. 3.68 ... 

Deposition of nickel at rates up to 1 mm/h in the concentrated solution is described by Kendrick . If pure nickel anodes are operated at a current density between 0-5 and 1-OA/dm in suiphamate solutions, a substance which behaves as a stress reducer is produced continuously in sufficient quantity that the stress in deposits can be varied at will from compressive to tensile by adjusting cathode current density and solution temperature. This finding is exploited with the concentrated suiphamate solution in the Ni-Speed processand in a further development cobalt is added to give deposits of... 

It is interesting to note that cobalt cobaltite, C03O4, is a good catalyst, too, for anodic chlorine evolution. In this case, too, a correlation is observed between the reaction rate and the spinel s defect concentration (amount of nonstoichiometric oxygen). 

Since the reaction between hydrogen and oxygen is very slow at room temperature, catalysts are incorporated in the carbon electrodes. At the anode, suitable catalysts are finely divided into platinum or palladium at the cathode, cobaltous oxide, or silver. The two halfreactions shown above yield the overall result as ... 

Mixing of the electrode products causes hydrolytic precipitation of the nickel and, after separation of the nickel hydroxide, the filtrate was returned to the cells. The sequence of the electrolytic purification steps is outlined in Figure 6.28. Nickel hydroxide slurry is first added to the anolyte for the purpose of raising the pH to 3.7 (2 H+ + Ni(OH) = Ni2+ + 2 H20), and iron(II) is oxidized by introducing chlorine. This causes hydrolytic precipitation of the iron(III) and corrects the nickel ion deficiency by the low anodic current efficiency. The iron(III) hydroxide is removed by filteration. The clarified solution is then treated with nickel carbonate and further chlorine to oxidize the cobalt(II) and allow its separation as cobalt(I II) hydroxide. 

Subcategory A encompasses the manufacture of all batteries in which cadmium is the reactive anode material. Cadmium anode batteries currently manufactured are based on nickel-cadmium, silver-cadmium, and mercury-cadmium couples (Table 32.1). The manufacture of cadmium anode batteries uses various raw materials, which comprises cadmium or cadmium salts (mainly nitrates and oxides) to produce cell cathodes nickel powder and either nickel or nickel-plated steel screen to make the electrode support structures nylon and polypropylene, for use in manufacturing the cell separators and either sodium or potassium hydroxide, for use as process chemicals and as the cell electrolyte. Cobalt salts may be added to some electrodes. Batteries of this subcategory are predominantly rechargeable and find application in calculators, cell phones, laptops, and other portable electronic devices, in addition to a variety of industrial applications.1-4 A typical example is the nickel-cadmium battery described below. 

Environmental tests have been combined with conventional electrochemical measurements by Smallen et al. [131] and by Novotny and Staud [132], The first electrochemical tests on CoCr thin-film alloys were published by Wang et al. [133]. Kobayashi et al. [134] reported electrochemical data coupled with surface analysis of anodically oxidized amorphous CoX alloys, with X = Ta, Nb, Ti or Zr. Brusic et al. [125] presented potentiodynamic polarization curves obtained on electroless CoP and sputtered Co, CoNi, CoTi, and CoCr in distilled water. The results indicate that the thin-film alloys behave similarly to the bulk materials [133], The protective film is less than 5 nm thick [127] and rich in a passivating metal oxide, such as chromium oxide [133, 134], Such an oxide forms preferentially if the Cr content in the alloy is, depending on the author, above 10% [130], 14% [131], 16% [127], or 17% [133], It is thought to stabilize the non-passivating cobalt oxides [123], Once covered by stable oxide, the alloy surface shows much higher corrosion potential and lower corrosion rate than Co, i.e. it shows more noble behavior [125]. 

Low-valent cobalt pyridine complexes, electrogenerated from CoCl2 in DMF containing pyridine and associated with a sacrificial zinc anode, are also able to activate aryl halides to form arylzinc halides.223 This electrocatalytic system has also been applied to the addition of aryl bromides containing an electron-withdrawing group onto activated alkenes224 and to the synthesis of 4-phenylquinoline derivatives from phenyl halides and 4-chloroquinoline.225 Since the use of iron as anode appeared necessary, the role of iron ions in the catalytic system remains to be elucidated. 

Just a few years after the discovery of the deposition and electroactivity of Prussian blue, other metal hexacyanoferrates were deposited on various electrode surfaces. However, except for ruthenium and osmium, the electroplating of the metal or its anodizing was required for the deposition of nickel [14], copper [15,16], and silver [9] hexacyanoferrates. Later studies have shown the possibilities of the synthesis of nickel, cobalt, indium hexacyanoferrates similar to the deposition of Prussian blue [17-19], as well as palladium [20-22], zinc [23, 24], lanthanum [25-27], vanadium [28], silver [29], and thallium [30] hexacyanoferrates. 

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