Organic pigments lead carbonate

Blocking pigments may adsorb at the active metal surface. They reduce the active area for corrosion and form a transport barrier for ionic species to and from the substrate. An example of this type is a group of alkaline pigments (lead carbonate, lead sulfate, zinc oxide) that may form soaps through interaction with organic oils. 

The thickness of the platelets can be adjusted by controlling the reaction conditions to produce interference colors. The pigment crystals are mechanically sensitive and show a fast sedimentation behavior because of the high density (6.4gcm 3). Agglomeration tendency and occupational health (toxicity) risks are the reason why Pb(OH)2 2PbC03 is not produced in powder form, but is flushed from the aqueous phase into suitable organic solvents or resins and handled as stabilized dispersions. Today, the application of basic lead carbonate is limited to artificial pearls, buttons, and bijouterie. 

Chromium metal is commercially produced in the United States by the reduction of chromite ore with carbon, aluminum, or silicon, and subsequent purification. Sodium chromate and dichromate are produced by roasting chromite ore with soda ash. Most other chromium compounds are produced from sodium chromate and dichromate (Hartford 1979 Westbrook 1979). For example, basic chromic sulfate (Cr(0H)S04), commonly used in tanning, is commercially produced by the reduction of sodium dichromate with organic compounds (e.g., molasses) in the presence of sulfuric acid or by the reduction of dichromate with sulfur dioxide. Lead chromate, commonly used as a pigment, is produced by the reaction of sodium chromate with lead nitrate or by reaction of lead monoxide with chromic acid solution (IARC 1990). 

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