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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 to ...
In conversion coating chromate reacts with these metals to prevent corrosion, retain electrical conductivity, and provide a finish for the appearance of the final alloy products. [3] This process is commonly used on hardware and tool items. Chromate species take on their distinctive yellow color when coated.
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]
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.
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.