Pitting Corrosion Behaviour of Monel-400 Alloy in Chloride Solutions

Pitting corrosion behavior of Monel-400 alloy in 3.5 wt pct NaCl sodium chloride solution has been investigated using the cyclic potentiodynamic anodic polarization technique. The effects of chloride ion concentration, pH values and different temperatures on the pitting parameters were determined. The morphology of the pits produced after anodic polarization treatments were inspected by scanning electron microscope (SEM). The results indicated that, the increase in chloride ion concentration shifts Epit and Eprot of the alloy toward negative values and the pitting potential is much more dependent on pH value in the basic region. The breakdown of passivity with increasing temperature may be due to kinetic changes of passivating films and dissolution rate of the alloy in its passive state.