Chromium coatings trivalent baths

Chromate conversion coating can be defined as the process where works are surface finished in baths containing hexavalent chromium [9]. Zinc plated steels, zinc, magnesium, aluminum, etc. in a chromate bath dissolve into the solution as ions and react with hexavalent chromium to form trivalent chromium. When the case of zinc plated steel is taken as an example, zinc on the surface dissolves as follows. 

The surface finishing process where hexavalent chromium ion would be issued (used) is mostly for chromate conversion treatment. Chromate is a chemical conversion coating process. This means that the surface finishing is by chemical reactions between chemical agents and materials. The chromate conversion treatment uses a chromate bath composed of hexavalent chromium ions. Currently trivalent chromate and some topcoats are used. 

Conversion treatments based on phosphates of trivalent chromium, which yield a deep emerald green layer. The baths comprise chromium anhydride, phosphoric acid and hydrofluoric acid. This type of conversion is widely used for products that are lacquered by the coil-coating process and used in the building industry. The weight of the layer ranges from 400 to 800 mg-m , and its thickness is roughly 400 nm for a deposition of 1 g-m . These layers combine good corrosion resistance with excellent adherence for lacquer. 

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