Anodes, aluminum platinum

The choice of cathode materials is less restricted by corrosion considerations than the choice of anodes so few metals react readily with the medium that their use is impractical. Some of the most popular electrode materials are mercury, lead, tin, copper, iron, aluminum, platinum, nickel, and carbon. 

The method described by ASTM B 457, Test Method for Measurement of Impedance of Anodic Coatings on Aluminum, is used to study the seal performance of anodized aluminum 141,1421. This method uses a 1-V rms 1-kHz signal source from an impedance bridge to determine the sealed anodized aluminum impedance. The test area is again defined with a portable cell, and a platinum or stainless steel auxiliary electrode is typically used. The sample is immersed in 3.5 % NaCl (see ASTM B 457). 

Kong, L.B., Li, M.L., M.K., Guo, X.Y. and Li, H.L. (2003) Morphology of platinum nanowire array electrodeposited within anodic aluminum oxide template characterized by atomic force microscopy. Chinese Physics Letters, 20, 753. 

Examples of the sacrificial-anode method include the use of zinc, magnesium, or aluminum as anodes in electrical contact with the metal to be protected. These may be anodes buried in the ground for protection of underground pipe lines or attachments to the surfaces of equipment such as condenser water boxes or on ship hulls. The current required is generated in this method by corrosion of the sacrificial-anode material. In the case of the impressed emf, the direct current is provided by external sources and is passed through the system by use of essentially nonsacrificial anodes such as carbon, noncor-rodible alloys, or platinum buried in the ground or suspended in the electrolyte in the case of aqueous systems. 

Molten Carbonate Fuel Cell The electrolyte in the MCFC is a mixture of lithium/potassium or lithium/sodium carbonates, retained in a ceramic matrix of lithium aluminate. The carbonate salts melt at about 773 K (932°F), allowing the cell to be operated in the 873 to 973 K (1112 to 1292°F) range. Platinum is no longer needed as an electrocatalyst because the reactions are fast at these temperatures. The anode in MCFCs is porous nickel metal with a few percent of chromium or aluminum to improve the mechanical properties. The cathode material is hthium-doped nickel oxide. 

A convenient method to produce porous surfaces is the anodic oxidation of aluminum plates. Such microstructured aluminum platelets have been coated by wet impregnation with Pt-, V- and Zr-precursors [35], and tested under catalytic methane combustion conditions. The conversion rate of oxygen followed directly the platinum content in the catalysts. These data were well reproducible even after five different runs. 

A library of 35 different catalysts fixed on electrochemically oxidized aluminum either in oxalic acid (Lib 1) or sulfuric add (lib 2) was tested at 450 °C and 1.1 bar. The methane-to-oxygen ratio was set to 1 in order to establish the potential of the catalyst to form intermediates. Figure 3.20 shows experimental results for a residence time of 550 ms and a screening time of 60 s. The conversion rate followed directly the platinum content in the catalysts. The higher the platinum content, the higher is the degree of conversion. Catalyst carrier formed by anodization of... 

Probably the most common solid electrode is platinum, although it dissolves anodically in some melts, for example in halides. The choice of gold and silver [86] is also frequently made. Graphite is very often used because it is cheap and can be obtained in a wide range of sizes and qualities. These electrodes can be used over long periods of time, and they have a wide electrochemical stability, both anodic and cathodic. Vanadium and molybdenum are also used in appropriate systems. Studies for the use of some inert anodes made of semiconducting ceramics have been made, especially for aluminum electrolysis [87],... 

Now that we have run through the two simple processes. Its time to move onto something a little more advanced. To review what we have learned so far, look at the two similarities between the two procedures we have done. In the first procedure we made ferrous chloride by electrolyzing a salt solution using an iron anode. In the second procedure we used a copper anode, and got cupric chloride. Now, you should remember that if we replaced the copper anode with zinc for example, we would get zinc chloride. Note Any metal can be used with the exception of lead, platinum, and a few others we need not discuss at this point. If you want, try it with aluminum, zinc, nickel, chromium, or magnesium to get the respective chlorides. Note The sodium chloride can be replaced with sodium bromide, or sodium iodide to make the corresponding bromides and iodides. 

Imidazole carboxylic acids are readily converted into hydrazides,436 acid halides,437 amides,437-439 and esters,439-440 and they may be reduced to alcohols with lithium aluminum hydride,441 and to aldehydes by controlled potential reduction.442 Anodic oxidation of l-methylimidazole-5-acetic acid (94) using cooled platinum electrodes yields l,2-bis(l-methylimidazol-5-yl)ethane (95).443... 

A = aluminum anode, K = copper cathode, R = ceramic frame, S = platinum power supply, B = contact socket, H = lid of indurated fabric... 

Sock and co workers [31] synthesized carboxylic acids by reducing alkyl bromides at platinum, gold, stainless steel, and graphite in the presence of carbon dioxide in either DMF or a THF-hexamethylphosphoramide (HMPA) mixture. Reduction of an alkyl monobromide at nickel in DMF containing TBABr and in the presence of an arylalkene and a sacrificial aluminum anode leads to an addition product [32]. 

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