Effects of Anionic Impurities on Chromium Plating

Abstract

By measureing the current efficiencies and by the Hull cell test, the unfavorable effect and the permissible amount of anionic impurities such as Cl^-, NO₃^-, and PO₄^3- were studied on the Sargent bath (CrO₃ 250 and H₂SO₄ 2.5g/l) and the bath contining sodium fluorosilicate (CrO₃ 250, H₂SO₄ 1.5, and Na₂SiF₆ 5.0g/l).
Each impurity decreases the current efficiency and brightness range. The permissible amount of each impurity is as follows:
Cl^- is 1g/l (as NaCl) for the both baths, NO₃^- 1g/l (as NaNO₃) for the Sargent bath and 2g/l for the sodium fluorosilicate bath, and PO₄^3- 4g/l (as Na₂HPO₄⋅12H₂O) for the both baths.
At the range of so low current density as not to deposit Cr, the base metal of copper, nickel, or iron dissolves into the both baths containing Cl^-.