Sacrificial pigment

Anticorrosive pigments may be classified by their mode of action, for example chemical and/or electrochemical (Active Pigments), physical (Barrier Pigments), and electrochemical/ physical (Sacrificial Pigments) [5.54—5.56]. 

Lead powder. The oil-suspension of metalhc lead powder is used in the preparation of protective primers for steelwork where it is normally present as the sole pigment. Lead pigments act as a barrier and provide a degree of sacrificial protection similar to that of zinc dust. 

Among many technological marvels from that era is a pigment known as Maya Blue. This startling, turquoise-like color was used extensively by the Maya for many purposes (Fig. 6.3). The Maya used the pigment for paint that was applied to sculpture, wall murals and pottery, among other objects. They also used the pigment to color the bodies of sacrificial victims before they were thrown into sacred wells or had their hearts cut out at temple altars. 

In addition to the inhibitive pigments, which contain the anodic, cathodic and mixed inhibitor types, those described earlier, there are two more classes of inhibitors commonly incorporated into protective coatings. These two inhibitor pigment types are barrier and sacrificial pigments. 

As a result, barrier pigments can be incorporated into primer, intermediate coat, or top-coat since they are chemically inert and do not react with the metal, unlike inhibitive or sacrificial... 

Sacrificial pigments usually contain zinc in the form of zinc dust in large amounts. When in electrical contact with the steel surface, the zinc film acts as the anode of a large corrosion cell and protects the steel cathode. In other words, zinc sacrificially corrodes instead of steel. In addition to sacrificially corroding, zinc dust also provides barrier action due to formation of its insoluble corrosion products. ... 

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