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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 ...
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 conversion coating (chemical film) per MIL-DTL-5541F for aluminium and aluminium alloy parts; A standard overview on black oxide coatings is provided in MIL-HDBK-205, Phosphate & Black Oxide Coating of Ferrous Metals. Many of the specifics of Black Oxide coatings may be found in MIL-DTL-13924 (formerly MIL-C-13924).
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
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 ]
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.
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.