Zinc and Calcium Ferrites

Only one zinc ferrite pigment has attained economic significance. Its properties are as follows [5.156]  

A trade name for zinc ferrite is Anticor 70 (Bayer, Germany Mobay Chemical Corporation, USA). 

Zinc oxide [1314-13-2], ZnO, Mr 81.37, is a white powder that is usually used in combination with active anticorrosive pigments. For a detailed description, see Section 2.3. It has the following physical properties  

The inhibiting action of zinc oxide is based on its ability to react with corrosive substances and to maintain an alkaline pH in the coating. It also reacts with acidic components of the binder to form soaps and absorbs UV light. 

The lead content of commercial zinc oxide depends on the manufacturer and is in the range 0.002-1.5%. For a zinc oxide coating to be considered lead-free, the lead content must be less than 1.5%. 

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Ferrite pigments appear to protect steel both by creating an alkaline environment at the coating-metal interface and, with certain binders, by forming metal soaps. Kresse [70,80] has found that zinc and calcium ferrites react with fatty acids in the binder to form soaps and attributes the corrosion protection to passivation of the metal by the alkaline environment thus created in the coating. 

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