The Effect of Temperature on Pitting Behavior and The Passive Film Characteristics of Alloy 600 in Chloride solution

The effect of temperature on pitting behavior and the passive film characteristics of Alloy 600 was investigated in deaerated 10,000 ppm chloride solution at 90∼280 .deg. C by anodic polarization, XPS, and transmission electron diffraction method. The pitting potentials decreased significantly with increasing temperature up to 220 .deg. C, and then decreased smoothly at higher temperatures. The pit morphologies were also dependent on temperature: isolated pits were developed up to 220 .deg. C, while broad pits occurred over the large surface at 280 .deg. C. The film formed at 90 .deg. C consisted of mainly chromium oxyhydroxide with significant bound water, whereas the content of non-protective nickel oxyhydroxide increased at 280 .deg. C. The film formed at 90 .deg. C showed an amorphous structure, however crystalline film formed at 280 .deg. C. It was suggested that the dependence of the pitting behavior on temperature was closely relate with the change in the above properties of the passive films