Abstract
Rapid scan, slow scan, potentiostatic and scratch techniques have been applied to determine the pitting potentials of Ni in 0.1, 1 and 7%NaCl solutions at 294, 323, 353 and 373 K. The lowest and most accurate pitting potentials are given by the potentiostatic techniques. The corrosion potentials obtained from these various electrochemical techniques are compared with the values of the pitting potential determined by the long term immersion tests. It is shown that the corrosion potentials attained prior to the onset of pitting in immersion tests are close to the values determined by the potentiostatic method. A critical pitting temperature (CPT) and critical crevice temperature (CCT) diagrams have been constructed on the basis of the exposure tests. The CPT diagram shows that there is both an upper and lower temperature limit for pitting corrosion on the basis of the existence of a reversal temperature observed during the determination of pitting potentials.
