Cathodes base plate

The step-by-step construction of the cathode base plate is described as follows ... 

It is possible to provide cathodic protection to base plate up to 1 720 MNm yield strength, by coupling to mild steel or possibly to zinc , but zinc and metals more active than zinc tend to induce hydrogen embrittlement. Welds up to 1 380 MNm may be cathodically protected by zinc, but at impressed potentials of — 1-25V (S.C.E.) both 1240 and 1380 MNm welds fail rapidly due to hydrogen embrittlement. Neither mild steel nor zinc couples protect AISI 4340 steel . 

A wide range of operating conditions and design philosophies affect mercury cell efficiency. For example, the fundamental distinction between a resaturation and a waste brine process influences the temperature and brine strength profile along the length of the cell and hence the overall efficiency. Another important factor is the quality of the brine. Impurities in the brine can cause base-plate deposits, which tend to reduce the anode/cathode gap. This gradual reduction in gap requires either manual or automatic adjustment and, eventually, the cell must be taken off-line and the thick mercury removed. 

In order to study cathode flooding in small fuel cells for portable applications operated at ambient conditions, Tuber et al.81 designed a transparent cell that was only operated at low current densities and at room temperature. The experimental data was then used to confirm a mathematical model of a similar cell. Fig. 4 describes the schematic top and side view of this transparent fuel cell. The setup was placed between a base and a transparent cover plate. While the anodic base plate was fabricated of stainless steel, the cover plate was made up of plexiglass. A rib of stainless steel was inserted into a slot in the cover plate to obtain the necessary electrical connection. It was observed that clogging of flow channels by liquid water was a major cause for low cell performance. When the fuel cell operated at room temperature during startup and outdoor operation, a hydrophilic carbon paper turned out to be more effective compared with a hydrophobic one.81... 

Fig. 6 ELTECH Systems M DC cells, (a) Brine feed rotometer (b) head sight glass (c) cell head (d) cathode frame assembly (e) tube sheet (f) base plate (g) cathode tube (h) base plate protector (i) DSA [3, p. 65].

The most common cell with horizontal electrodes is the mercury cell from the chlor-alkali industry (see Chapter 3). The mercury cathode flows down the slightly sloping base plate of the cell and many rectangular dimensionally stable anodes (DSA) (of gauze or expanded-metal-type structure to allow the chlorine gas to rise with only minimum restriction) are mounted from the top of the cell so that they cover the surface area of the mercury and give an inter-electrode gap of a few centimetres (see Fig. 2.13). The cell may be as big as 70 m. The brine is, however. 

The latter was made possible by redrilling the base plate to accommodate a closer anode spacing. As a result, the cell designations have been changed as MDC-55 to MDC-66, H2-A-42 to H2-A-50, and H-4-75 to H-4-93. Substitution of copper for steel in the design of the cathode tube supports is another change instituted in the ADCT . 

Parallel planar geometries are used in some high-frequency triodes. A planar cathode is placed at the base of the tube, and a heavy planar plate is anchored at the top of the tube, with a flat-mesh control grid inserted between the cathode and plate. Close spacing between the plate and cathode is obtained in this manner so that electron-transit time from the cathode to the plate is minimized. 

Attach each carbon fabric cathode electrode to the top of the PVC support with a cable tie around the titanium wire and PVC, so that the end attached to the underwater cable is pointed toward the base plate. 

Cathode (Positive Plate). The cathode consists of a depolarizer and a current collector. These depolarizers are powders and are nonconductive. In order for the depolarizer to function, a form of carbon is added to impart conductivity a binder is added for cohesion, and a metal grid is used as a current collector, a base for the cathode, to facilitate intercel connections and battery terminations. Possible cathode formulations are shown in Table 17.3... 

Eig. 19. CME monopolar electrolyzer a, membrane b, cathode element c, half-cathode element d, current distributor e. Teflon tube f, CI2 + depleted brine manifold g, conductor rod h, CI2 + depleted brine outlet nozzle i, base frame j, recycled NaOH manifold k, recycled NaOH inlet nozzle 1, gasket (the gasket-to-element ratio is quite small) m, tie rod n, anode element o, H2 + NaOH manifold p, end plate, q, under cell bus bar (simplifies piping... 

Eig. 20. Cut view of Chlorine Engineers membrane bag cell a, manifold b, frame c, partition plate d, sealing plug e, recirculated NaOH inlet f, cathode g, anode h, cathode can i, membrane bag j, base k, butterfly valve 1, feed brine m, depleted brine n, caustic outlet. 

Fig. 11. Ion plating configurations (a) plasma-based, where the substrate fixture is the cathode of the d-c circuit, and (b) vacuum-based (IBAD).

Hard plating is noted for its excellent hardness, wear resistance, and low coefficient of friction. Decorative plating retains its brilliance because air exposure immediately forms a thin, invisible protective oxide film. The chromium is not appHed directiy to the surface of the base metal but rather over a nickel (see Nickel and nickel alloys) plate, which in turn is laid over a copper (qv) plate. Because the chromium plate is not free of cracks, pores, and similar imperfections, the intermediate nickel layer must provide the basic protection. Indeed, optimum performance is obtained when a controlled but high density (40—80 microcrack intersections per linear millimeter) of microcracks is achieved in the chromium lea ding to reduced local galvanic current density at the imperfections and increased cathode polarization. A duplex nickel layer containing small amounts of sulfur is generally used. In addition to... 

Copper-base alloys will corrode in aerated conditions. It is, therefore, sometimes appropriate to consider cathodic protection. It becomes particularly relevant when the flow rates are high or when the design of an item causes the copper to be an anode in a galvanic cell (e.g. a copper alloy tube plate in a titanium-tubed heat exchanger). Corrosion can be controlled by polarisation to approximately — 0-6V (vs. CU/CUSO4) and may be achieved using soft iron sacrificial anodes. 

Swedish iron is sometimes used as galvanic wastage plates in heat exchangers, particularly for marine applications. This is possibly based on tradition, since it cannot be the most economical method in the light of current cathodic-protection practice. The material is not currently used as an impressed-current anode. 

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