Is chloride corrosion related to pH?
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Is there a direct relationship between chloride ion corrosion and pH? If there are any relationships, what are they? We welcome everyone to come and discuss, so as to learn together and improve.
This topic is quite representative; sometimes, when things are unclear, incorrect judgments can be made. Everyone is welcome to discuss it.
Haha, Teacher Wang has become an official moderator now :victory:
This post was last edited by Wang Wei2 on 2019-1-4 at 13:52. Is there a direct relationship between chloride ion corrosion and pH level? The answer is yes, there is a relationship. If there are any relationships, what are they? First, we should know that the rate of metal corrosion is related to three factors: temperature T, pH value, and the corrosive medium. If one of these factors changes, the corrosion of the metal will change as well; or, if all three factors change unpredictably, there will be N different patterns of corrosion in the metal. When assuming normal temperature. The relationship between chloride ions and pH changes. We know that metals also corrode when the pH level is above 7 (alkaline conditions). In such cases, the corrosion film formed on the metal is relatively dense; this film is known as a passivation layer, and it prevents the corrosive agents from continuing to damage the metal. Although the presence of a certain amount of chloride ions causes little or no damage to the metal. When the pH value of the metal is less than 7 (acidic), corrosion occurs; the rust products resulting from this corrosion are relatively loose and cannot form a passivation layer. We call this the activated state of the metal surface. This is due to the presence of chloride ions, which cause electrochemical corrosion at the activation sites on the surface of the activated metal, leading to corrosion and damage of the metal. In short, when chloride ions are present in the liquid, metal corrosion is reduced at alkaline pH levels. When the pH value is acidic, metals are prone to severe pitting or stress corrosion.
Everyone is welcome to share different opinions?
There are many conditions; factors such as the components of the solvent and temperature play a role.
If all other conditions remain constant, what is the state of chloride ion corrosion considering only pH?
Generally, acidic conditions tend to cause greater corrosion; when the pH is low, such as between 7 and 9, corrosion is less likely to occur. However, when the pH is above 9, alkaline corrosion is more likely to take place, such as in the case of alkali embrittlement.
Thank you, Teacher Wang. I would like to ask which materials are sensitive to alkaline corrosion?