Studies were carried out on the anodic behaviours of stainless steels in HNO
3 containing halogen ions.
The results obtained were as follows:
(1) In HNO
3 solution containing halogen ions, the critical current density in active state was larger than in H
2SO
4 solution.
(2) Of the halogen ions added to HNO
3 solution, the one that had the strongest action in preventing the passivation of metallic Ni was found to be Br
- ion, while for Fe, Fe-Cr, Fe-Ni and Fe-Cr-Ni alloys it was Cl
- ion.
(3) The oxidation action of HNO
3 made Ni and Fe-Ni alloys depolarize, and, thereby, the anodic dissolution of Ni and Fe-Ni was made much easier than that in H
2SO
4 solution. But Fe-Cr alloys which become passive easily were found to become passive as soon as they are set as alloy anodes.
While in the passive state, the oxidation action of HNO
3 had the two effects: one makes the passive film steady and the other inhibits the indirect dissolution reaction as Cr
6+→Cr
3++3
e-by Cl
- ion.
View full abstract