Impressed current systems oxygen

Example 3.7 Iron corrosion in oxygen-saturated solution and evaluation of impressed current-cathodic protection system. 

Fig. 15.7 Effect of diffusion rate of oxygen on the impressed current protection system.

Overactive cathodic protection— which can occur particularly with magnesium anodes—or badly controlled impressed current protection—leads to the reduction of oxygen to form hydroxyl ion (OH ), which can attack paints. Also, the placing of the zinc anodes requires experience in connection with both type and thickness of the paint (system). Since zinc anodes do not allow the production of excessive amounts of alkali, paint failure or the need to use alkali-resistant paints is avoided. 

When an impressed current cathodic protection (ICCP) system is in full operation there is a high possibility for oxygen to be produced at the anode, and in nearly all cells, hydrogen is formed at the cathode. If chloride ions are present, chlorine gas may be formed at the anode. This generation of gas, either oxygen or chlorine, at the anode is not nearly as likely to occur in a natural corroding cell as it is when an ICCP system is used, particularly when inert anodes are used. 

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