Abstract
The corrosion resistance and electrochemical behavior of two commercial nickel alloys, one a Nickel-Molybdenum alloy (N10675) and the other a Nickel-Chromium-Molybdenum (N06200) alloy were investigated in pure hydrochloric acid and HCl solutions containing different levels of ferric ions. Oxidizing ferric ions are commonly encountered in various chemical processes, and they markedly affect the corrosion behavior of the alloys, even at ppm levels. It was of interest to use electrochemical techniques to compare the anodic behavior of the alloys since the classic immersion tests do not yield sufficient knowledge regarding the effect of ferric ions on their corrosion behavior. Standard polarization resistance and potentiodynamic polarization test methods were used. The results clearly showed that the electrochemical behavior of the two alloys was drastically affected by the addition of ferric ions in the acidic solutions. The Ni-Mo and Ni-Cr-Mo alloys were resistant to general corrosion in pure HCl at ambient temperature; however in HCl solutions containing ferric ions, the Ni-Mo alloy showed poor corrosion resistance, while the Ni-Cr-Mo alloy exhibited excellent corrosion resistance when the level of ferric ions was higher than 250 ppm, because of passivation.
