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Chromium is a steely-gray, lustrous, hard metal that takes a high polish and has a high melting point. While chromium metal and Cr(III) ions are not considered toxic, hexavalent chromium, Cr(VI), is both toxic and carcinogenic. 85 % of the available chromium is used in metal alloys. The remainder is used in the chemical, refractory, and foundry industries. Chromium compounds are used in leather products, dyes, paints, cement, mortar and are anti-corrosives. Chromium salts (chromates) are allergic to some people. Chrome ulcers are often found in workers that have been exposed to strong chromate solutions in electroplating, tanning and chrome-producing manufacturers [1, 2]
Anodic oxide coatings are formed on the metallic job by an electrochemical process known as anodizing. The process is carried out in an electrolytic cell where a job is made of an anode and a suitable inert metal as a cathode (Figure 3.1). When the electric current of sufficient voltage is passed through a suitable electrolyte the metal surface is converted to an adherent oxide coating which is an integral part of the substrate [1–4].
Chemical conversion coatings are one of the most common surface modification techniques that provide a barrier between metal and its surrounding environment . The treatment can be carried out by dipping, spraying or by application of brush. The term chemical conversion is used where the exposed metal surface gets converted into the chemically inert inorganic coating by a chemical or electrochemical process. The coatings, in addition to corrosion protection, may impart requisite functional properties, enhanced surface hardness and a good base for application of subsequent paints, lubricants, adhesives, etc. The properties of these coatings depend on the kind of substrate metal, the composition and structure of the coatings. On the other hand, the composition and structure of the coatings depend on the bath composition and operating parameters of the process.