Anode cathode gap

Anode-cathode gap 500 pm Inlet and outlet hole diameter 2 mm... 

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. 

As with previous methods, artificially layered deposits may be obtained from a single chemical solution using a specially designed cell, for instance, with adjustable anode-cathode gap (see Fig. 17.3). This two-compartment cell may be constructed from Lucite with deposition conducted in one compartment, and KC1 solution placed in the other. A calomel reference electrode immersed in this KC1 solution should be coupled to the flat-plate cathode by a salt bridge, ending in a capillary on the deposition side. The specimen electrode is fixed, and the counter-electrode is movable using, say, a micrometer. Electrodeposition is best conducted under quiescent conditions. 

The derivation for the gas amplification does not take into account the effect of the drifting positive ions in a proportional counter. Indeed, due to the narrow amplification region, around the anode wire, practically all the charges are created in a very small volume. These ions drift rather slowly away from the wire. They tend to reduce the electric field around the wire. If a second photon is detected at the same position on the wire, the field and consequently, the gas amplification will be lower. Since the density of the positive ions, in the anode-cathode gap increases... 

Table 2 shows the values as calculated for two anode-cathode gap thicknesses, anode wire diameters (2a) and spacings between them (s) (see Fig. 11). 

The Hooker-Uhde Monopolar Membrane electrolyzer is shown in Figure 19. The active electrode surface of the HUMM electrolyzer is 1.7 m per cell element. The cell elements consist of anode frames of titanium and cathode frames of steel. Anode-cathode gap is approximately 3 mm. A separate frame is provided for holding the membrane. The electrode block rests on a support structure that serves as the header system for electrolyte and electrolysis products. Peformance of this electrolyzer is reported to be 2750 KWH/M ton NaOH at 35% caustic soda and 95% current efficiency at 3 KA/M current density (65). 

The cells are strong steel boxes, lined with alumina (to act as a refractory), a thermal insulator, and carbon. The cathode is a liquid pool of aluminum that lies at the base of the cell, above a current collector consisting of a number of carbon blocks inlaid with steel bars. A frozen crust of electrolyte protects the cell housing from erosion. The cell has ports for the periodic addition of alumina through the crust, for the removal of A1 metal, and an extractor to vent anode gases (mainly CO2). As the carbon anode is consumed, it is lowered to maintain a constant anode/cathode gap (about 5 cm). In a typical plant for the production of 70,000 tons of A1 per year, 200 Hall-Heroult cells, each 3 m X 8 m in size with 15 m of anode area, are arranged in series. The operating current density is... 

Figure 21. Dependence of cell voltage on anode-cathode gap at 90°C and at a current density of 20A/dm2 (NaOH concentration 35 wt. % Anolyte concentration 3.5 TV reproduced with permission from the authors and Society of Chemical Industry, London).

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 anodes are carbon blocks and the cathodes are the tank and/or mild steel coils also used for water cooling of the electrolyte. In a cell under normal operating conditions a separator is not essential provided the anode—cathode gap is more than a critical distance, commonly about 4 cm. The product gases, fluorine and hydrogen, must be kept apart and this is achieved with a nickel or monel skirt which dips into the electrolyte surface and directs the anode and cathode gases into different collection vessels. A typical cell will have 20—40 anode blocks and will operate at a total current of 1000—10 000 A. 

Although polarization can be controlled to some extent, it is never fully overcome and this, combined with the anode—cathode gap of about 5 cm necessary... 

The cell design is very simple. It consists of a bipolar stack of 50—200 rectangular carbon steel sheets whose cathode faces are electroplated with cadmium to a thickness of 0.1—0.2 mm the anode—cathode gap is fixed at about 2 mm by... 

As with the mercury cell, the introduction of metal anode technology led to a considerable review of cell design and the opportunity to optimize the anode-cathode gap, which as with the mercury cell, increased with time as the anode deteriorated, but unlike the mercury cell, could not be adjusted with the cell in service. Diaphragm technology improved, with the replacement of wet... 

H-4/84(orLCD) The LCD (low current density) cell operated with about 12% lower current density by reducing the anode-cathode gap, and allowing for more anode and cathode fingers in the shell of the H4 cathode... 

In addition, anode wear caused the anode-cathode gap to increase with time, resulting in increased cell voltage and energy consumption. Various attempts to reduce the degradation of graphite were not completely successful [4]. 

In the 1960s, the technology of choice to produce chlorine was the mercury cell, in part because of its ability to operate at high current densities. Therefore, DS As first operated commercially in mercury cells, where rapid gas release was very important. The anode designs [107] used in mercury cells to accomplish the quick release of chlorine, so that the anode-cathode gap could be lowered and the NaCl strength in this space maintained at high levels, are shown in Fig. 4.5.18. BafBes on the back of the active anode surface are claimed [108] to provide sufficient gas lift to force the brine into the space between the anode and cathode. 

The anodes are titanium coated with oxides of Ru, Ir, and Ti and are placed in groups from carrying devices with the ability to change the height (and hence the anode-cathode gap) manually, hydraulically, or by motor. Each cell can be short-circuited externally by a switch. The cell bus bars are generally copper but... 

The Olin cells [68] have machined steel cell bottom units with rubber-lined steel side channels and steel tops. The anode stems are sealed through individual flexible rubber sleeves and are suspended from a copper channel, which also carries the current from the flexible buses to the anodes. Olin has developed a novel system to mount and adjust the anode-cathode gaps. The U-shaped copper or aluminum bus bar, located above each row of anodes, provides support to the anode lifting gear and current to the anodes, which are bolted to it. The anodes can be adjusted manually or electronically with the remote computerized anode adjusted (RCAA) system. 

The cell is made of steel with cathodes welded to the tub-like container. The cylindrical graphite anodes are independently suspended and inserted through the cell s refractory covers. This arrangement allows adjustment of the anode-cathode gap as the graphite oxidizes in the aqueous medium. The magnesium collects in its chamber in front of the cell and is periodically withdrawn for further processing. 

The tank cell is the classical batch or semi-batch reactor of electrochemical technology. In most tank cells, the electrodes are vertical and made from sheet, gauze or expanded material. The cell is arranged with parallel lines of alternate anodes and cathodes, the electrodes extending across and to the full depth of the tank. The anode-cathode gap is made as small as possible to maximize the space-time yield and to reduce the energy consumption. It is unusual in tank cells to induce convection by mechanical means, but electrolyte stirring is in generally promoted... 

The design of the cell will affect all the figures of merit for an electrolytic process. Cell design will be considered in detail in section 2 5 but it should be noted here that the principal factors determining the electrolysis performance will be the presence or absence of a separator and its type (porous diaphragm or ion-selective membrane), the mass transport regime, the arrangement and form of the electrodes (hence, the anode-cathode gap and potential distribution at both electrodes) and the materials of construction ... 

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