Titanium-based anodes

In the examples following in which the invention is demonstrated in whole or in part by electrodialysis, the electrodialysis unit is a cell pair comprised of a single coated titanium base anode common to two cells in the following sequence ... 

Coatings do not have the durability of the coated titanium-based anodes. However, they are less expensive, easier to apply and can be repaired and maintained easily. They are not suitable for continuously wetted abraded or trafficked surfaces. They require excellent surface preparation to get good adhesion. 

Ter Heijne, A., Hamelers, H.V.M., Saakes, M., and Buisman, C.J.N. (2008) Performance of non-porous graphite and titanium-based anodes in microbial fuel cells. Electrochim. Acta, 53 (18), 5697-5703. 

Chen Z, Belharouak I, Sun Y-K et al (2013) Titanium-based anode materials for safe lithium-ion batteries. Adv Funct Mater 23 959-969... 

Hayfield, P. C. S. and Warne, M. A., Titanium Based Mesh Anodes in the Cathodic Protection of Concrete Reinforcing Bars , presented at UK Corrosion, Brighton (1988)... 

The dimensionally stable anodes (DSA ) consist of a titanium base metal covered by a thin conducting layer of metal oxide or mixed metal-oxide oxides. Since their discovery by Beer (1966) in the late 1960s, a lot of work has been done on DSA and on finding and preparing new coating layers for many electrochemical... 

A typical mercury cell is shown in Figs 3.3 and 3.4. It consists of a large, shallow trough, dimensions 15 m x 2 m x 0.3 m, with a steel base which slopes slightly from end to end so that the mercury can flow along the bottom of the cell. The coated, expanded titanium DSA anodes (see Fig. 3.1), each of approximate dimensions 30 cm X 30 cm, enter the cell from the top and are arranged parallel to the mercury surface with an anode-cathode gap of about 1 cm. The cell will have about 250... 

The major workhorse of the diaphragm-cell electrolysis is the ELTECH electrolyzer, H-4 and MDC-55. There are several conunon features in these cell designs, as can be seen in Fig. 5.17. The base of the cell is a copper plate with spot faced holes to anchor the anodes (Fig. 5.18). It also acts as a current conductor. Either a sheet rubber cover or a titanium base cover using rubber rings around the anode posts protects the copper base. 

ADCT includes increased active area. Advanced technology cathodes (ATC ), Energy saving anodes (ESAtM), Polyramix diaphragms, zero-gap operation, titanium base covers (Tibac ) and Telene ... 

In chloride electrolyte systems, titanium anodes with iridium or ruthenium compound catalytic coatings are used to allow evolution of chlorine at the anodes. For these anodes, each short circuit from nodules and dendrites not only destroys the local active coating and its catalytic effect but also completely destroys any ability for that area to oxidize chloride to chlorine. Shorts thereby reduce the life of these anodes which is important since these anodes are relatively expensive compared to lead alloy anodes normally utilized in sulphate based systems. The use of such catalytic anodes is expanding with some sulphate electrolyte copper electrowinning plants now moving to a form of these titanium catalytic anodes a nickel plant has these anodes for mixed chloride/sulphate duty and there appears scope for further expansion into nickel sulphate electrowinning. 

Extending the operating life in existing chloride based and mixed sulphate/chloride systems of titanium catalytic anodes for nickel and the future application of such anodes to purely sulphate systems... 

The mercury cell actually consists of two cells. The brine cell or electrolyzer is a long, slightly sloped trough containing purified brine. At the bottom of this trough is a thin sheet of metallic mercury that flows under the brine and constitutes the cathode. Projecting above the cathode is the anode assembly, which consists of horizontal blocks of graphite or titanium-based, dimensionally stable anode (DSA). 

Owing to its catalytic activity, ruthenium dioxide (RuO,) is used extensively in industrial anodes for the chlor-alkali industry and the production of perchlorates. These ruthenium-dioxide-based anodes consist of a thin catalytic layer coated onto a titanium base metal. Iridium-dioxide-based anodes are used for the production of persulfates, in electroplating, and in hydrometallurgy for evolving oxygen. These composites anodes, because of their corrosion resistance in chloride-containing media or concentrated acids and their ability to decrease the overpotential of chlorine and oxygen evolution, are called by the trade name dimensionally stable anodes (acronyms DSA ). Other uses are in fuel cells electrodes electrocatalysts. 

As a general rule, these anodes are made from a titanium base metal covered by a rutile layer TiO doped by RuO (30 mol.%). They were used extensively in the industry (e.g., De Nora, Magnetochemie, Permelec, Eltech Systems Corp., US Filter, and Heraeus) and today they are used in all chlor-alkali processes and in chlorate production. The dimensionally stables anodes for chlorine evolution are described in the technical literature by the brand acronyms DSA (RuOj) and DSA -Cl2, and they enjoyed great success in industry for two reasons first, ruthenium has the lowest price of all the PGMs and, second, its density is half that of its neighbors. Moreover, its electrocatalytic characteristics for the evolution of chlorine are satisfactory. In industrial conditions (2 to 4 kA.m ) the service life of these electrodes is over 5 years. Therefore, today, titanium is the only base metal used for manufacturing dimensionally stable anodes for chlorine evolution. The contribution of Beer s discovery to the development of industrial electrochemistry is very important The reader can also find a complete story of the invention of DSA as told by the inventor himself and written on the occasion of his receiving the Electrochemical Society Medal award. 

As stated in the introduction, Ta coating may be used as substrate in the preparation of DSA oxygen electrodes it consists of a thin and porous layer of Iridium oxide, which acts as catalyst, obtained by thermal oxidation of an iridium compound on a valve metal. The lifetime of the anode in water electrolysis in extreme conditions of polarization (anodic current = 50 A/m ), acid concentration (30% m/m) and temperature (T = 80°C) is sensitive to the corrosion resistance of the valve metal This is shown on table I [24], which standardized life time (lifetime reported for the mass surface density of the catalyst Ir02) for some varieties of titanium base alloys and a tantalum coating as substrate ... 

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