2018 Volume 67 Issue 8 Pages 336-345
The rusting of stainless steel in an atmospheric environment is mainly caused by dew droplets. However, the dew behaviors such as dew forming and drying that lead to rusting have not been fully clarified yet. In this study, the dew behaviors were precisely analyzed by the in-situ microscopic observation under the atmospheric condition simulating real environment.
The dew forming process progresses with 2 phenomena: the growth of the single droplet and the coalescence with another one. The mass of the sea salt in a single droplet increases by these phenomena.
The dew drying process is divided into three stages: the pinning stage when the contact angle of the droplet decreases, the de-pinning stage when the contact area of the droplet decreases, and the self-pinning stage when the contact angle decreases furthermore. At the self-pinning stage, the salt starts to precipitate and the rust forms under and beside the precipitation.
It is considered that those behaviors of dew forming and drying cause the formation of the rusting pattern on the stainless steel; a number of small rusted points are distributed uniformly.