Traditional Lead and Chromate Pigments

Basic lead silicochromate (4(PbCr04 PbO) -t 3(Si02 4 PbO)) reached certain industrial importance. It was developed to replace red lead. The pigment is a so-called core pigment, in which the active pigment substance (PbCr04) is precipitated onto an inert core (Si02). Because this anticorrosive contains both lead and hexavalent chromium, it has lost its previous economic importance as well [5.53, 5.56]. 

For very specific and limited applications the following lead-based products have been used lead suboxide, lead carbonate and lead cyanamide (mirror coatings), lead silicate (electro disposition primers), dibasic lead phosphate, tribasic lead phosphate silicate, and calcium plumbate [5.51, 5.53]. 

Chromates have long been utilized as anticorrosives. The anticorrosive action of chromates is based on the content of a certain amount of water-soluble chromate within these pigments (Table 5.3). 

ISO 1249 - Zinc chromate pigments - Basic zinc potassium chromate pigments and zinc tetrahydroxychromate pigments - specifies the requirements, and corresponding test methods for zinc chromate pigments suitable for use in paints and/or corrosion-inhibiting coatings [5.59]. 

The requirements on strontium chromate pigments are specified in ISO 2040 -Strontium chromate pigments for paints [5.60]. Required characteristics for zinc potassium chromate, zinc tetrahydroxychromate and strontium chromate are summarized in Table 5.4. 

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