Anode-to-cathode distance

On each side of this stainless steel piece, securely clamp into place two pieces of graphite, roughly equal in size, having a total surface area in contact with the solution of about 70 cm. All three of these electrodes should run straight down into the flask, and a constant distance of 1 cm should separate the surface of the anodes from the cathode. This is very important, as the anode to-cathode distance determines the voltage at which this cell runs. It is also very important that shorts between the anode and cathode be prevented. The current must flow anode-to-cathode through the solution, not through a short ... 

In the case of a diaphragm or membrane chlor-alkali cell, there are three ohmic drops to consider anode to separator, cathode to separator, and across the separator. The anode to cathode distance in ELTECH s H-4 cell is 7.74 imrt, the thickness of the diaphragm is 3.05 mm, and the cathode to diaphragm distance is negligible. The anode to diaphragm ohmic drop, // a/s. niay now be estimated from the conductivity data of the electrolytes, which are presented in the appendix to this section. 

The current efficiency of an actual HaU-Heroult (HH) ceU depends on internal interactions in the magnetohydrodynamic (MHD) flow, reactions in different zones of the cell, electrical contact system, operating parameters, and anode-to-cathode distance, hi principle, Haupin and Frank [65] developed a model of relevant zones within the HHceR. This model is shown in Figure 7.12 and it suggests that the possible interactions that are related to current efficiency and energy consumption may be attributable to diverse potentials in the these zones... 

Proton-transfer efficiency depends on the distance between the two electrodes, the type of membrane used, and the type and concentration of buffer. At present, there is no standard method to measure the proton transfer efficiency. It can only be qualitatively determined by the pH difference between the anode and cathode chambers. According to the diffusion theory, reducing the anode-to-cathode distance facilitates the proton transfer. Should the electrodes be too close to each other, there will be adverse effects on the activities of microorganisms [60]. 

Since there is a fixed current for a given applied voltage, it follows that c must be linear in distance across the cell, y. Now i+>0 and z+-z >0, so dcldy < 0 that is, the concentration of cations decreases from anode to cathode. The potential drop is also in the same direction. From charge neutrality c+/c = constant, so the anion distribution behaves similarly to the cation distribution, which was noted earlier in the discussion of the characteristics of the electrolytic cell. 

The migration of Na" cations in the electrical field from anode to cathode is the desired membrane function. A Na" cation is attracted by the negatively charged fixed ions. But it remains movable because the distance between the fixed ions is so small that jumping from one to the next needs little energy. Thus, a Na" ion can nearly unhindered glide on the walls of the cluster structure, even through the small channels. 

Table 13 Factors by which material losses in the anodic material in contact with the cathodic material is raised at an area ratio anode to cathode of 1 4 (anode/cathode distance 0.2 cm)...

It is known that current is transported from the anode to the cathode by ions in the electrolyte and in the metallic path from the anode to cathode. Because of the normal high conductivity of metals, almost no resistance is offered to the current flow in the metallic path. However, resistance can be encountered if the distance between the anode and the cathode is appreciable. 

One underlying factor is the anode-to-cathode separation distance. In general, too close a separation distance results in a poor distribution, as depicted in Fig. 11.9. A trade-off that must be made, when increasing this distance, is the increased resistance to current flow. At excessive distances, the overall protection levels of a structure may be compromised for a given level of power supply. Additional anodes can be used to achieve a more homogeneous ionic current flow, where an optimum anode-to-cathode separation distance cannot be achieved. 

Relatively high anode to cathode separation distance... 

Where no coatings are used on the cathode surface of a closed system, the area of optimum protection should cover a 2.5 1 spacing. If the closest anode to cathode spacing is 0.3 m (1 ft) and a potential of 1000 mV is obtained, a potential of at least 850 mV will be achieved at 0.75 m (2.5 ft) distance from this anode. 

At the end of each experiment, residual hydrocarbon content in soil was estimated by a Soxhlet technique at 3 points 0.25, 0.5, 0.75 anode to cathode dimensionless distance concentration values are normalized respect to the initial concentration condition an presented as percentage. Results are shown in Figure 12 for carbon felt (CF) cathode, and in Figure 13 for titanium (Ti) cathode. 

V across 18 mm distance between the plates resulted in an anode-to-cathode potential difference of about 2 V at each electrode. 

The optoelectronic properties of the i -Si H films depend on many deposition parameters such as the pressure of the gas, flow rate, substrate temperature, power dissipation in the plasma, excitation frequency, anode—cathode distance, gas composition, and electrode configuration. Deposition conditions that are generally employed to produce device-quahty hydrogenated amorphous Si (i -SiH) are as follows gas composition = 100% SiH flow rate is high, --- dO cm pressure is low, 26—80 Pa (200—600 mtorr) deposition temperature = 250° C radio-frequency power is low, <25 mW/cm and the anode—cathode distance is 1-4 cm. 

Corrosion occurs at the anode, where metal dissolves. Often, this is separated by a physical distance from the cathode, where a reduction reaction takes place. An electrical potential difference exists between these sites, and current flows through the solution from the anode to the cathode. This is accompanied by the flow of electrons from the anode to the cathode through the metal (Fig. 8). 

When a battery produces current, the sites of current production are not uniformly distributed on the electrodes (45). The nonuniform current distribution lowers the expected performance from a battery system, and causes excessive heat evolution and low utilization of active materials. Two types of current distribution, primary and secondary, can be distinguished. The primary distribution is related to the current production based on the geometric surface area of the battery constmction. Secondary current distribution is related to current production sites inside the porous electrode itself. Most practical battery constmctions have nonuniform current distribution across the surface of the electrodes. This primary current distribution is governed by geometric factors such as height (or length) of the electrodes, the distance between the electrodes, the resistance of the anode and cathode stmctures by the resistance of the electrolyte and by the polarization resistance or hinderance of the electrode reaction processes. 

Both reactions indicate that the pH at the cathode is high and at the anode low as a result of the ion migration. In principle, the aeration cell is a concentration cell of H ions, so that the anode remains free of surface films and the cathode is covered with oxide. The J U curves in Fig. 2-6 for anode and cathode are kept apart. Further oxidation of the corrosion product formed according to Eq. (4-4) occurs at a distance from the metal surface and results in a rust pustule that covers the anodic area. Figure 4-2 shows the steps in the aeration cell. The current circuit is completed on the metal side by the electron current, and on the medium side by ion migration. 

A 600-ml., tail-form beaker is equipped with a thermometer, a magnetic stirring bar, and two electrodes. A 45-mesh cylindrical platinum anode (Note 1) is used. Surrounding the anode is a cylindrical nickel cathode (Note 2). The electrodes are held in place (distance between anode and cathode 0.75 cm.) and suspended in the beaker by means of a clamp formed from Delrin rods (Note 3). The electrodes are connected to an adjustable d.o. power supply (Notes 4, 5). 

The proximity of the anodes to structures is also important. For example, if the sacrificial anodes are placed on, or very close to, steel pipework in soil then the output from the face of the anodes next to the steelwork can be severely limited. Alternatively, in high conductivity environments, corrosion products may build up and wedge between the anode and the structure. The resulting stresses can lead to mechanical failure of the anode. On the other hand, when anodes are located at an appreciable distance from the steelwork, part of the potential difference will be consumed in overcoming the environmental resistance between the anode and cathode. 

Continuous Anodes Consist of considerable lengths of relatively flexible copper-cored material which can be contoured to suit restricted spaces or to distribute current in a localised fashion. Typically they may be used in water boxes at a non-ferrous tubeplate/ferrous water box junction. Anode terminations pass through the water box via insulating entry points and the anodes are supported on insulators within the box. Anode/cathode distance must be such as to prevent the anode becoming engulfed in calcareous deposit that forms on the cathode. 

The schematic diagram of the arc discharge apptcratus is shown in Fig. 1. Two graphite rods wrae used as the anode with the diameter of 10 mm and the cathode with the diameter of 6 mm. The anode was controlled until the distance between the anode and cathode was very small to approx. 1 nun. 

In terms of mechanism analysis, one of the most useful features of the peak current is its proportionality to concentration and, even more important, its proportionality to the square root of the scan rate. The peak potential is independent of scan rate and concentration and provides easy access to the standard potential E° (at 25°C, the peak potential is 28.5 mV more negative than the standard potential). At the same temperature, the peak width is 56.5 mV. Another diagnostic criterion is the distance between the anodic and cathodic peak potentials, 2.22(7ZT/F) (i.e., 57 mV at 25°C). 

A large number of commercial cells put the anode and cathode comparatively close together, but, in order to obtain reasonably high purity in the gaseous products, a porous partition is placed between the electrodes this, like inaeasing the distance between the plates, aeates a certain amount of resistance, but it has one advantage of the latter procedure in that it makes for compactness, which is very desirable in any plant and particularly so in the case of electrolytic ones, as one of the greatest objections to their use is the floor space which they occupy. 

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