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Chromate conversion coating or alodine coating is a type of conversion coating used to passivate steel, aluminium, zinc, cadmium, copper, silver, titanium, magnesium, and tin alloys. [ 1 ] : p.1265 [ 2 ] The coating serves as a corrosion inhibitor , as a primer to improve the adherence of paints and adhesives , [ 2 ] as a decorative finish, or ...
The Cronak process is a conventional chromate conversion coating process developed in 1933 by The New Jersey Zinc Company. [1] It involves immersing a zinc or zinc-plated article for 5 to 15 seconds in a chromate solution, typically prepared from sodium dichromate and sulfuric acid. [2]
A conversion coating is a chemical or electro-chemical treatment applied to manufactured parts that superficially converts the material into a thin adhering coating of an insoluble compound. These coatings are commonly applied to protect the part against corrosion , to improve the adherence of other coatings, for lubrication , or for aesthetic ...
Cadmium chromate is the inorganic compound with the formula CdCrO 4. It is relevant to chromate conversion coating , which is used to passivate common metal alloys such as aluminium , zinc , cadmium , copper , silver , magnesium , and tin . [ 2 ]
Zinc chromate, Zn Cr O 4, is a chemical compound, a salt containing the chromate anion, appearing as odorless yellow powder or yellow-green crystals, but, when used for coatings, pigments are often added. [2] [3] [4] It is used industrially in chromate conversion coatings, having been developed by the Ford Motor Company in the 1920s. [5]
Chromate containing minerals are rare. Crocoite, PbCrO 4, which can occur as spectacular long red crystals, is the most commonly found chromate mineral. Rare potassium chromate minerals and related compounds are found in the Atacama Desert. Among them is lópezite – the only known dichromate mineral. [10]
Aluminium chromate conversion coatings are amorphous in structure with a gel-like composition hydrated with water. [18] Chromate conversion is a common way of passivating not only aluminium, but also zinc, cadmium, copper, silver, magnesium, and tin alloys. Anodizing is an electrolytic process that forms a thicker oxide layer.
The process steps can typically involve chromate conversion coating the entire component, followed by a masking of the surface in areas where the chromate coating must remain intact. Beyond that, the chromate coating is then dissolved in unmasked areas. The component can then be anodized, with anodizing taking to the unmasked areas.