Nitric Acid

STATION 8. Nitric Acid

The purpose of the nitric acid post-treatment for electropolishing is to dissolve the film of chemical byproducts that form as the electrochemical reactions proceed. These byproducts consist primarily of the sulfates, phosphates and chromates of heavy metals, and are very difficult to remove by water rinsing alone.

If left untreated, these byproducts leave a milky or translucent film on the surface of the parts. After drying or in later storage, the film hardens to a crusty white residue which degrades the appearance of the finish, providing growth sites for bacteria and initiation sites for corrosion. A short rinse in dilute nitric acid at room temperature dissolves the byproducts, producing work of maximum specularity.