Tecnoseal Answers - Materials Part 2: Galvanic Scale
Let's continue the discussion that began last week on the materials that form the sacrificial anodes by introducing a vital topic to define which metals are best to use in alloys: the galvanic scale.
We have seen that when we install an anode our main objective (even if not the only one) is to protect the metals that make up your boat from the corrosion generated by immersion in water.
This corrosion of metals can not be avoided at all, so if you want to protect them you need to "cover" them with other more active metals. Such active metals become the anodes of the structure under examination and the amount of material sacrificed thereof is committed to protecting the structure itself. Hence the name "sacrificial anodes."
All metals tend to be oxidized. For some, however, this process occurs more easily and for this reason they corrode more than the others. The relative index that determines the corrosion rate can be traced from the galvanic scale.
In the galvanic scale the elements are in increasing order of nobility (from bottom to top). Therefore, at the base we find those with a lower electrochemical potential. These in the cathodic reaction will be those that will corrode becoming anodic area if in continuity with a more noble element.
Furthermore, the metals closest to each other in the galvanic scale will have a lower tendency to create strong galvanic pairs if in contact. It follows that their coupling in the presence of an electrolyte will be much less dangerous than with the use of two metals very distant from each other in the scale.
...continue next week