What chemical is used for passivation?
Passivation uses nitric acid, and less commonly, citric acid to treat metal. Nitric acid is suitable for many grades of stainless steel, titanium, and aluminum but can also be adjusted when there is a higher risk of flash attacks.
Flash attacks describe a dull grey layer that forms after passivation instead of the intended fine finish. Sodium dichromate can be added to the nitric acid solution to reduce the risk of flash attacks and the concentration of nitric acid can also be adjusted to prevent etching.