Rolled anodes

However, concerns about the toxicity of cadmium have accelerated the replacement of these batteries by nickel-metal hydride batteries, described in Section 9.3.5. In nickel-cadmium (nicad) batteries, the anode is cadmium and the cathode is an unstable nickel oxyhydroxide, formed in the unusual conditions found in the cell, and written variously as Ni(OH)3 or NiO(OH). It is generally formed together with stable nickel hydroxide, Ni(OH)2. The electrolyte is NaOH or KOH. The anode and cathode are assembled in a roll separated by a cellulose separator containing the electrolyte. The cathode/separator/anode roll is contained in a nickel-plated stainless steel can (Figure 9.10). The cell voltage is 1.3 V but the working voltage is usually nearer to 1.2 V. The schematic cell reactions are as follows. 

Figure 4 shows the relation between the current density and the anode potential for various types of anode. The anode potential of Pb-0.52 wt% Ag - 0.50 wt% Ca anodes annealed after rolling is lower than that of the Pb-0.99 wt% Ag conventional anode and that of the same chemical composition of as-cast anode. However, the anodes annealed without rolling showed high values of the anode potential compared to that of the as-cast anodes for current densities over 70 mA/cm. The values of the anode potential for the anodes rolled and not aimealed were high compared to these of the as-cast anodes, and for this reason, these values were not plotted. It can be observed that the rolled Pb-Ag-Ca anodes must be further annealed in order to obtain a decrease in the anode potential during the electrolysis process. 

Roll cell. These are sandwich constructions consisting of a packed stainless steel or titanium mesh cathode, separator and a screen anode rolled up like a swiss roll. These cells can operate with fluid velocities of 1-10 cm s and with apparent current densities of 10-200 mA cm at the separator. This type of cell is a concentrator device for metal ions, the metal is recovered from the cell by leaching or by anodic dissolution. An economic analysis [23] showed that waste water treatment with this cell is highly competitive with ion-exchange technology. Typical applications for metal ion removal are recovery of copper and Hg from waste stream recovery of Ag from a used fixer solution down to a silver concentration of 0.1 ppm and the treatment of zinc cyanide plating bath rinse waters which contain the Zn(CN)5 complex ion. 

Anodes are not attached to the rudder but are situated between the rudder shaft and the ship s wall and connected via a copper strip. The propeller is protected via a slip ring on the shaft. To achieve a low-resistance contact, the divided copper or bronze ring has a rolled silver-bearing surface on which metal graphite brushes slide. The transmission voltage should be below 40 mV. 

The submitters used a cathode of nickel foil (140 x 71 x 0.5 mm.) rolled into a cylinder 3.5 cm. in diameter surrounded by three curved platinum anodes each having the dimensions 70 x 30 x 1 mm. (total surface area 130 cm. ) with a distance of 0.5-1 cm. between the cathode and the anodes. The submitters electrolyzed for 6 hours at a current maintained at 3.25 amp. This corresponds to a total of 19.5 amp.-hours and an anodic current density of 0.025 amp./cm.Under these conditions the submitters report yields of 81-84%. 

It should be noted that the rechargeable cells discussed later have the same construction and differ only in separator type, electrode composition and cathode / anode balance. For comparison, Fig. 3 shows the design of an AA-size lithium cell. The construction with a spirally rolled electrode increases the power output. 

The cell used (Fig. 16) is an undivided, so called Swiss-roll cell (Figs. 16 and 17) with a Ni mesh anode and a steel cathode. 

Fig. 16. Swiss roll electrolysis cell [198] (1) separator (2) anode sheet (3) cathode sheet...

Fig. 17. Schematic diagram of the flow system used for batch and continuous oxidation of DAS (Diacetone-L-sorbose) with a swiss roll cell with an anode area of 3 m2...

In the USA Andco Chemical Corp. and Niagara Environmental Assoc., Inc. have widely used this procedure for the treatment of cooling tower blowdown waters and in treatment of metal finishing process streams. The undivided cell geometry makes use of cold-rolled steel plates as anodes. Disadvantages of this procedure Formation of second streams, e.g. large amounts of sludges which must be dumped or treated. 

Swiss Roll Cell This cell has been developed in Switzerland [89]. A commercial application is one oxidation step at a NiOOH anode in alkaline solution for the vitamin C production [22]. Mesh electrodes of stainless steel (cathode 1) and nickel (anode 3) are rolled up together with spacers of polypropylene mesh (2,4) on the central current feeder (5) and mounted in a cylinder (cells up to 1 m diameter, 200 m active area). The electrolyte streams axially through the cell. 

Groseclose (21) used anodic polarization to electrochemically rate uncoated steel. It was necessary to employ a specific electrolyte (lOmM NaCI/25 mM sodium tetrafIuoroborate) and electrochemicaIly cleaned cold rolled steel. Two different lots of steel with identical primer exhibited grossly different salt fog performance. The bottom halves (uncoated) of the same panel tested... 

When an anode contains an appropriate amount of metals (or metal oxide), novel carbon materials such as SWNTs, metallofuJlerenes, filled nanocapsules, bam-boo -shaped tubes (23), nanochains (10), and MWNTs filled with metal carbides (24,25) are formed. Especially SWNTs are now attracting a great deal of interest from researchers in physics and materials science, because exotic electronic properties that vary between semiconducting and metallic states depending on how a graphene sheet is rolled (i.e., diameter and helical pitch of a tube) are predicted theoretically (26-28) and because unique quantum effects are revealed experimentally (29,30). 

The modified supported powder electrodes used in the experiments hitherto described on the anodic activity of CoTAA are out of the question for practical application in fuel cells, as they do not have sufficient mechanical stability and their ohmic resistance is very high (about 1—2 ohm). For these reasons, compact electrodes with CoTAA were prepared by pressing or rolling a mixture of CoTAA, activated carbon, polyethylene, and PTFE powders in a metal gauze. The electrodes prepared in this way show different activities depending on the composition and the sintering conditions. Electrodes prepared under optimal conditions can be loaded up to about 40 mA/cm2 at a potential of 350 mV at 70 °C in 3 M HCOOH, with relatively good catalyst utilization (about 5 A/g) and adequate stability. 

For laboratory scale conversions a simple beaker-type cell (Fig. 1) is convenient When lower current densities have to be applied or in big scale operations 21,26) the Swiss-roll cell is of advantage. The latter cell (Fig. 2) contains a rolled-up sandwich, consisting of an anode and cathode sheet and a separator net. This allows a high electrode area applied in a small cell volume, which results in the low current densities necessary for efficient electrolyses at the nickel hydroxide electrode. 

Fig. 2 Swiss-roll -cell, arrangement of the electrodes 1 Steel net cathode 2,4 Polypropylene net as insulating separator 3 Nickel net anode 5 Current feeder...

As shown in Fig. 12.4, aluminum electrolytic capacitors usually consist of an aluminum foil with a thin film of anodically-formed aluminum oxide (dielectric), an aluminum foil, an electrolyte solution, and a separator. The whole sandwich is compactly rolled and packed in a container. The electrolytic capacitors are in wide use, because of their small sizes, high capacitances, and low prices. However, the characteristics of electrolytic capacitors are apt to deteriorate with time. Recently,... 

As soon as the current is turned on, lead chromate begins to roll off the anode and fall to the bottom of the cell. Very little adheres to the anode plate. After about 2 hr., shut off the current and allow the suspended particles to settle. Decant the clear liquid, wash the precipitate with hot water by a second decantation, collect the solid on a filter, and dry it in the air oven. The yield should be very nearly quantitative for the current used. 

The heterogeneously catalyzed Mn02-mediated oxidation of diacetone-L sorbose to diacetone-2keto-L sorbic acid, the latter being a precursor to vitamin C, at nickel anodes and based on the chemical oxidation of the substrate by NiOOH is of technical relevance. The limiting current density in 1 M KOH solution is under operation conditions only 10 A/cm2 leading to relatively poor space-time yields. Robertson and Ibl showed that acceptable space-time yields can by obtained by using thin layer cells of Swiss roll type (193, 194), which leads to an efficient compression of the cell width to fractions of a millimeter. 

Place three soaked sheets of filter paper on the anode, one on top of the other The sheets should be saturated, but not dripping with excess buffer. Place the sheet of wet membrane on top of the filter paper stack and cover with the gel. Roll a glass rod (or similar) over the surface of the gel to push out any air bubbles, and to ensure good contact between the gel and the membrane. Finally, place the three remaining sheets of soaked filter paper on top of the gel... 

Electrical conductive-wire contacts, terminals, switch pans, bus bars Hardware cotter pins, nails, rivets, soldering copper, ball floats Other, anodes, chemical process equipment, kenles, pans, printing rolls, expansion plates, rotation bands, die-pressed forgings... 

Figure 22.12 Swiss-Roll cell for the applications of NiOOH electrodes (1 = steel net cathode 2 + 4 = polypropylene net 3 = nickel net anode 5 = current feeder).

Rolls and other relatively simple shapes make use of inert shields and thieves to avoid edge buildup and produce a more even plate thickness. For more complicated shapes having deeper recesses thicker deposits from cyanide copper baths have been used as an undercoat to the copper sulfate deposit. Acid copper baths operate near 100% efficient over a wide current density range. The cathode efficiency is usually slighdy less than the anode efficiency, bringing about a slow increase in copper unless drag-out losses are high. 

Scheme of the galvanisation setup with (1, 2) rolling cathodes, (3) chemically metallised yarn, (4) electrolyte solution, (5) galvanisation bath and (6) anodes. 

The concept of monolithic module design is associated with Argonne National Laboratories [111, 112]. Power density of about 8 kW/kg or 4kW/1 and fuel efficiency over 50% are expected to be achieved with monolithic SOFCs. The monolithic structure started with a co-flow version where the cell consists of a honeycomb-like array of adjacent fuel and oxidant channels that look like corrugated paperboard, as shown in Fig. 42. Multilayer laminates of the active cell components (anode-elec-ttolyte-cathode) are appropriately corrugated and stacked alternatively between flat multilayer laminates in the following sequence anode- interconnection material-cathode. Tape casting [111] and hot-roll calendering [113, 114] are used to fabricate the monolithic structure. A cross-flow version where oxidant and fuel channels are... 

The section of H-in. tubing which runs through the insulator acts both as an electrical connection to the anode and as an exit for the fluorine. A piece of 0.0032-in. sheet nickel 3K in- square rolled into a cylinder serves as an electrode, and it is bolted to the center of a disc of copper which covers the bottom of, and is firmly fastened to, the diaphragm. With such a combination, fluorine is liberated on the nickel but not on the copper. A thermometer well of copper tubing is fastened to the cover of the pot. 

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