The most representative formula for chromate passivation solution in China has been in use for over two decades. After such a long period of time, it has proven to be practical and feasible. Its main component is sodium dichromate, which is relatively inexpensive. By adding a certain amount of concentrated sulfuric acid and water to sodium dichromate, the solution can be prepared. 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.
