Effect of alternating temperature on passivation characteristics of carbon steel in chloride-free saturated Ca(OH)₂ solution

Passivity of carbon steel was examined in saturated Ca(OH)(2) solution with different alternating temperatures. The results showed that the Fe3+/Fe2+ and OH-/O(2-& nbsp;)ratios decreased, and donor density in the passive film increased with the amplitude of temperature alternation. Cracks were observed in the film when the sample experienced a higher amplitude of temperature change. Passive films on the samples in 20-50 ?& nbsp;and 20-60 ?& nbsp;alternating temperature solution were less stable than those of their counterparts in 40 ?& nbsp;and 50 ?& nbsp;solution, respectively. Furthermore, a model was proposed to explain the degradation of passive films under alternating temperature.