Anodizing voltage

It should be pointed out that external polarization differs from the unbiased (open circuit) case in that after application of, say, an anodic voltage only the oxidation reaction takes place on the metal, whereas the cathodic reaction (H — H2) occurs at the external counter-electrode. 

Fig. 5. Energy requirements of the HaH-Hfiroult cell (23—25). E, decomposition of alumina Eg, depolarization by carbon E, anode overvoltage E, counter electromotive force E, bath voltage drop E, bath bubble voltage F/, anode voltage drop Eg, cathode voltage drop E, external voltage drop ...

In dilute HE solutions and higher anodic voltages, the siUcon is dissolved in the tetravalent state ... 

Fig. 9-5 Voltage cone of horizontal anodes with the z axis at right angle to the anode = voltage anode/pipeline = voltage of ground at Z against remote ground.

Fig. 9-16 Interference of a short (a) and a long (b) pipeline by the anode voltage cone Hill region of cathodic polarization region of anodic polarization.

Experience shows that in interference by the anodic voltage cone, no unacceptable anodic interference is caused by an interference voltage Uy < 0.5 V versus the remote ground. The distance from the impressed current anode at which Uy = 0.5 V depends on the anode voltage, f/, and the anode length, L [ 13]. It amounts to ... 

No damaging interference to foreign objects has to be considered in cathodic protection with galvanic anodes because of the small current densities in soil and the lower anode voltages. 

Fig. 9-17 Interference of a long (by shorting insulating joints) and a short pipeline by an anode voltage cone 1 km in length P - potential measuring point / = insulating...

Fig. 9-20 Pipe/soil potential of a pipeline with defect-free PE coating (up to 200 m) and with bitumen coating (200 to 600 m) in the region of an anodic voltage cone...

For installations with several storage tanks and a protection current of several tens of an mA, uniform protection current distribution should be the goal, so that the current injection occurs via a number of anodes distributed over the site or via a more distant anode bed. Dividing up the protection current over several anodes avoids large local anodic voltage cones and therefore effects on neighboring installations. 

In this case, impressed current protection with several anodes was chosen on the one hand to achieve uniform current distribution with the relatively high protection current density, and on the other hand to avoid large anode voltage cones. A transformer-rectifier with a capacity of 10 V/1 A was chosen. 

Fig. 12-6 Local cathodic protection of a tank farm in high-resistance soil using the anodic voltage cones of distributed anodes the lines indicate soil potential values for an increase of 0.5 V relative to a remote ground numerical pairs volts.

The protection current requirement for aluminum ships is considerably less because of the dense adherent oxide films. The necessary protection current requirement is being clarified in current investigations [24] but good results have been obtained by assuming a figure of 10% of that for steel. With aluminum there is only a very narrow permissible potential range [25] (see Section 2.4) so that impressed current protection cannot be used because of the anodic voltage cone and only selected anode materials can be considered. 

Fig. 18-5 Current distribution in the interference of a borehole well casing by an anodic voltage cone.

Table 24-1 Calculation formulas for simple anodes (anode voltage Uq = IR)...

Anodising the formation of oxide films on metals by anodic oxidation of the metal in an electrolyte solution. The term can be used for thin dielectric films but is more particularly applied to thicker films formed on some metals such as aluminium at higher anodic voltages. 

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