Anodic dissolution of chromium at high current densities in sodium nitrate electrolyte

The dissolution mechanism of pure chromium at high current density characteristic for electrochemical machining processes is studied. The combination of electrochemical, microscopic, and spectroscopic techniques leads to a comprehensive interpretation of the dissolution mechanism. The polishing quality increases with increasing nitrate concentration and current density, respectively. The oxygen evolution amounts up to 45% of the consumed anodic charge and the apparent valence of the chromium dissolution decreases with increasing applied potential down to z = 3.5. The authors explain this phenomenon by a passive dissolution of chromium via Cr3+ followed by a chemical oxidation of Cr3+ to dichromate under nitrate reduction to nitrogen.