The most representative formula for chromate passivation solution has been in use for over two decades. After such a long period of testing, it has proven to be practical and feasible. The main component of this formula is the relatively inexpensive sodium dichromate. The solution can be prepared by adding a certain amount of concentrated sulfuric acid and water to sodium dichromate. The specific formula is as follows:
Sodium dichromate (Na₂Cr₂O₂·2H₂O): 0.4-0.6%;
Sulfuric acid (H₂SO₄) (98%): 0.1%;
Water (H₂O): the remainder.
There is also a chromic acid passivation solution composed of chromic anhydride, concentrated sulfuric acid, and water, but it is more expensive. The formula is as follows:
Chromic anhydride (CrO₃): 0.4-0.6%;
Sulfuric acid (H₂SO₄) (98%): 0.1%;
Water (H₂O): the remainder.
Some factories add 4-5% sodium hydroxide (NaOH) to this formula.
