A Study of the Relation between Current Oscillations and Pitting

Anodic polarization behaviors of iron in pure H2SO4 and three mixed acidic solutions, H2SO4 NaCl，H2SO4 NaNO3 and H2SO4 NaCl NaNO3, were investigated. The potentiodynamie sweep curves showed that the current densities rose and dropped irregularly in H2SO4 NaCl solution at the more anodic potentials since the iron surface suffered pitting attack in the solution, but the pitting corrosion was inhibited effectively in the presence of nitrate ions. The surface morphological measurements indicated that pits appeared on the iron surface in H2SO4 NaCl solution and only a few unobvious corrosion spots were observed in H2SO4 NaCl NaNO3 sointian after the iron electrode was potentiostatically polarized at 1.3 V. The oscillatory properties of iron are associated with the susceptlbility of the iron to pitting. In H2SO4 NaCl solution, the regular potentiostatic current oscillations gradually evolved into the irreg-niar current fluctuations due to occurrence of the pitting; whereas in H2SO4 NaCl NaNO3 solution, the current oscillations took place regularly, like the oscillatory behavior in the pure H2SO4 solution. Thus, when the higher the oscillatory fre-quency, the more irregular oscillatory process and the more sensitive to pitting iron occurred.

A Study of the Relation between Current Oscillations and Pitting

Anodic polarization behaviors of iron in pure H 2SO 4 and three mixed acidic solutions, H 2SO 4+NaCl, H 2SO 4+NaNO 3 and H 2SO 4+NaCl+NaNO 3, were investigated. The potentiodynamic sweep curves showed that the current densities rose and dropped irregularly in H 2SO 4+NaCl solution at the more anodic potentials since the iron surface suffered pitting attack in the solution, but the pitting corrosion was inhibited effectively in the presence of nitrate ions. The surface morphological measurements indicated that pits appeared on the iron surface in H 2SO 4+NaCl solution and only a few unobvious corrosion spots were observed in H 2SO 4+NaCl+NaNO 3 solution after the iron electrode was potentiostatically polarized at 1 3 V. The oscillatory properties of iron are associated with the susceptibility of the iron to pitting. In H 2SO 4+NaCl solution, the regular potentiostatic current oscillations gradually evolved into the irregular current fluctuations due to occurrence of the pitting; whereas in H 2SO 4+NaCl+NaNO 3 solution, the current oscillations took place regularly, like the oscillatory behavior in the pure H 2SO 4 solution. Thus, when the higher the oscillatory frequency, the more irregular oscillatory process and the more sensitive to pitting iron occurred.