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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 ...
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 ...
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.
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 ]
Additionally, his research established that nanocoatings are a more effective and eco-friendlier substitute for chromate conversion coatings, as they need less metal pretreatment and are non-toxic. It was demonstrated that a coating as thin as 90 nm can decrease copper's corrosion rate by three orders of magnitude in a harsh sour-acid environment.
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]
Hexavalent chromium plating solution is used for both decorative and hard plating, as well as bright dipping of copper alloys, chromic acid anodizing, and chromate conversion coating. [2] A typical hexavalent chromium plating process is: Activation bath; Chromium bath; Rinse; Second rinse
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.
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