How are sodium chromate and sodium dichromate used in metal surface treatment?

Sodium chromate and sodium dichromate are industrially important salts derived from the chromium oxidation state of +6. In the context of metal surface treatment, these compounds serve several critical functions:

• Corrosion Protection: Sodium dichromate is specifically utilized for cleaning and protecting metals from corrosion.1
• Surface Treatment Applications: Chromium chemicals, including these salts, are employed in various processes such as the anodizing of aluminum and the treatment of zinc and magnesium surfaces.2
• Dips and Inhibitors: They are used in chemical dips for iron, steel, brass, and tin to enhance surface properties. Additionally, they act as corrosion inhibitors for brines and recirculating water systems.2

While these salts are foundational to surface treatment, it is important to note that chromic acid (produced by treating sodium dichromate with sulfuric acid) is the primary chemical used for electroplating processes, such as decorative and hard chromium plating.34