Common characteristics of corrosion (manual bonus points)
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After some thought, I was able to identify three common characteristics of corrosion: 1. From a thermodynamic perspective, corrosion is a process in which a metal undergoes a spontaneous transition from a non-stable state to a stable state； 2. It are chemical and electrochemical processes ； 3. It always occurs on the surface, starting from the surface. Let’s pool our ideas to see if we can identify more common characteristics of corrosion
At first, the corrosion rate is slow, but it speeds up as time goes on. I’m not sure if it’s right
For example, in some cases corrosion actually results in the formation of a passivation layer or protective layer, which means the process starts slowly, then speeds up, and then slows down again
Regarding the passivation layer, taking 304 as an example: its passivation layer is inherent to it； It still doesn’t exist on its own; when exposed to acid, a reaction occurs that results in the formation of a passivation layer ； Will it thicken its own passivation layer in response to an acid when encountered in the future?
This post was last edited by Wang Genrong on 2016-1-7 at 09:17. 1. The corrosion rate generally changes with temperature. 2. Water is often involved in the corrosion process under low-temperature conditions. 3. Corrosion under high-temperature conditions is often caused by the contact between oxygen or oxidizing gases and solid substances, resulting in corrosion.
For stainless steel, when acid washing is used for passivation, it removes the iron and iron oxides from the surface of the stainless steel; in other words, it eliminates the chromium-poor layer on the surface, resulting in the formation of a chromium-rich oxide film. At this point, if the material comes into contact with acid or other corrosive substances, it will have corrosion resistance. Of course, the passivation layer does not thicken, as all the substances that were supposed to react have already done so
Corrosion may start slowly and then speed up, or start fast and then slow down; in summary, the corrosion rate is represented by a curve