Cathodic protection in soils

The current in the soils also determines the electrophoretic migration of water from the anodic surfaces, which tend to dry out, to the cathodic ones, which tend to saturate. Part of the current is delivered not only through the soil itself but also through all the materials interfered with. Cathodic protection in soils should therefore be carefully designed, realized, and put into operation, taking into account not only of the environmental conditions and of the material properties to be protected but also of neighboring structures, the characteristics of coatings, and their evolution over time. 

The reference electrode generally used for monitoring cathodic protection in soils is the copper sulfate electrode. This consists of an electrode of electrolytic copper in a solution saturated with copper sulfate crystals. However, the most universal reference electrodes are of the silver chloride type. These consist of a silver wire, plate, or mesh coated with silver chloride so that both silver and silver chloride are in contact with a chloride ion rich electrolyte. The potential of the Ag/AgCl reference electrode will depend upon this chloride ion concentration. 

When metals other than steel are to be cathodically protected in soils, different potentials to a copper sulfate reference may be used as a criterion of protection. For lead-sheathed cables, a customary value is -0.70 V. For aluminum, the potential should be held between the limits of -1.00 and -1.20 V. 

Cathodic protection uses an impressed direct current (dc) supplied by any low output voltage source and a relatively inert anode. As is the case in all forms of cathodic activity, an electrolyte is needed for current flow. Cathodic protection and the use of protective coatings are most often employed jointly, especially in marine applications and on board ships where impressed current inputs do not usually exceed 1 V. Beyond 1 V, many coating systems tend to disbond. Current source for cathodic protection in soils is usually 1.5 to 2 V. 

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See also in sourсe #XX -- [ ]

See also in sourсe #XX -- [ ]

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