Discharge from Galvanic Anodes

The current-density-potential graph for a working galvanic anode is given by Eq. (6-8) in which the polarization resistance /j, is dependent on loading  

I/r is the rest potential. The difference between the potential of the working anode and the protection potential of the object to be protected is termed the driving voltage U.  

This function together with the linear behavior of the resistance of the protection system is shown in Fig. 6-1. 

Here 7 X is the protection current, 5 is the surface area of the anode, and and are the grounding resistances of the anode and the object. Information on the 

If the working point does not lie in the unpolarizable region (e.g., on account of the action of surface films) then instead of Eq. (6-12), 

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Sacrificial-anode-type cathodic protection systems provide cathodic current by galvanic corrosion. The current is generated by metallically connecting the structure to be protected to a metal/alloy that is electrochemically more active than the material to be protected. Both the structure and the anode must be in contact with the electrolyte. Current discharges from the expendable anode through the electrolyte and onto the structure to be protected. The anode corrodes in the process... 

Each galvanic cell in a lead-acid battery has two electrodes—one made of a lead(lV) oxide (Pb02) plate and the other of spongy lead metal, as Figure 17.17 shows. In each cell, lead metal is oxidized as lead(lV) oxide is reduced. The lead metal is oxidized to Pb ions as it releases two electrons at the anode. The Pb ions in lead oxide gain two electrons, forming Pb ions at the cathode. The Pb ions combine with S04 ions from the dissociated sulfuric acid in the electrolyte solution to form lead(ll) sulfate at each electrode. Thus, the net reaction that takes place when a lead-acid battery is discharged results in the formation of lead sulfate at both of the electrodes. 

Figure 18.3 Position of the decomposition energies of electrolytes relative to the potentials of the anode (reductant is oxidized by discharge) and the cathode (oxidant is reduced by discharge) of a galvanic cell for (a) solid electrodes with fluid electrolyte and (b) fluid electrodes with solid electrolyte. (From Goodenough in Ref. 1.)...

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