THE EFFECT OF TEMPERATURE ON THE PITTING BEHAVIOR AND PASSIVE FILM CHARACTERISTICS OF ALLOY 600 IN CHLORIDE SOLUTION

摘要

The pitting behavior and passive film characteristics of Alloy 600 were investigated in deaerated 10,000 ppm chloride solution in the temperature range of 90 to 280 deg C by anodic polarization, x-ray photoelectron spectroscopy, and transmission electron diffraction method. The pitting potentials decreased significantly with increasing temperature up to 220 deg C, and then decreased slowly at higher temperature. Pit morphologies were also dependent on the test solution temperature; isolated pits were developed up to 220 deg C, while pit broadening occurred over the large surface area at 280 deg C. The film formed at 90 deg C consisted of mainly chromium hydroxide with sufficient bound water having an amorphous structure, whereas the content of non-protective, crystallized nickel hydroxide/oxide increased at 280 deg C. From the results of this study, it was suggested that the dependence of the pitting behavior on temperature was closely related with the changes in the properties of the passive films.