The Principles of Galvanic Protection
Zinc has a higher electro-motive potential than iron or steel and in the presence of an electrolyte (moisture) will be attacked to protect the steel. Zinc ions go into solution, liberating electrons which cause a current flow into the steel to prevent ferrous ions from going into solution and beginning the electro-chemical corrosion cycle.
To function anodically, the zinc particles must be in intimate contact with one another so that the film itself is conductive. This is achieved in ZRC and Galvilite by the high zinc loading (95% by weight in the dry film), mixed in a special binder that does not insulate the zinc particles either from each other or from the base substrate.
Initially, the protection provided by ZRC is wholly that of galvanic action. As the zinc is sacrificed, zinc corrosion products are formed through the reaction of zinc ions with moisture and carbon dioxide. Zinc hydroxycarbonates and other zinc salts form in the film making the coating denser and reducing its conductivity. Thus the anodic action of the zinc continues until the film is converted into a dense, impervious barrier, resistant to weather, water and fume attack. However, if the coating is damaged, fresh zinc metal is readily available to provide renewed galvanic action.
Thus, the protection afforded by ZRC and Galvilite is twofold; cathodic protection and barrier protection. Essentially, it is a self-healing film as any damage to the barrier initiates renewed galvanic action.