The pitting behavior and passive film characteristics of Alloy 600 (UNS N06600) were investigated in deaerated 0.282 M sodium chloride (NaCl) solution in the temperature range from 90°C to 280°C using anodic polarization, x-ray photoelectron spectroscopy, and transmission electron diffraction. The pitting potentials decreased significantly with increasing temperatures up to 220°C and then decreased slowly at higher temperatures. Pit morphologies were also dependent on the test solution temperature; isolated pits were developed up to 220°C, while pit broadening occurred over a large surface area at 280°C. The film formed at 90°C consisted of mainly chromium hydroxide with a large amount of bound water and an amorphous structure. However, the concentration of non-protective, crystallized nickel hydroxide/oxide (Ni[OH]2/NiO) increased at 280°C. From the results of this study, it is suggested that the temperature dependency of pitting behavior is closely related to the changes in composition and structure of the passive films.
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Hur et al. (2006) studied this question.
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