SustainabilityNews

How difference of surface corrosion and pitting corrosion?

07-08-2023

Surface corrosion and pitting corrosion differ in the following ways:

Surface Corrosion: Surface corrosion refers to the corrosion that occurs on the surface of a metal, where the metal surface is not deeply eroded or penetrated by corrosion to the extent that it becomes pitted or significantly damaged.

Pitting Corrosion: Pitting corrosion is corrosion that develops on the metal surface over an extended period, causing the metal surface to be deeply eroded and penetrated into the metal substrate. This leads to significant damage to the metal, rendering it unsuitable for use.

Corrosion Mechanism:
When a metal undergoes oxidation or is subjected to reduction, the corrosion process takes place, resulting in the erosion of the metal. Therefore, the primary goal of corrosion prevention is to inhibit the occurrence of oxidation reactions. The most resistant metals to corrosion are those with the highest positive electrode potentials, such as gold. Platinum, silver, and red gold also possess good resistance to corrosion due to their relatively high positive electrode potentials. On the other hand, other metals are more susceptible to oxidation, meaning they are more likely to corrode easily.

An example of a commonly encountered and distinct corrosion process is the formation of rust on iron or the creation of iron oxide. Iron corrodes when there is the presence of oxygen and water. The corrosion process of iron is relatively complex and has unique characteristics. However, it is believed to involve critical steps, including:

1. Oxidation reaction occurs at a specific area on the iron surface, acting as the anode. This can be represented by the equation: Fe(s) Fe2+(aq) + 2e-
2. Oxygen is reduced at another area of the iron surface, acting as the cathode. In the presence of water, the equation becomes: 2O2(g) + 4H2O(l) + 8e- 8OH-(aq)
3. A subsequent reaction involves the formation of iron hydroxide: 4Fe2+(aq) + 8OH-(aq) 4Fe(OH)2(aq)

These steps contribute to the formation of iron oxide, commonly known as rust, and the overall corrosion process of iron.

It's important to note that the corrosion mechanisms and reactions can vary based on the specific metal, environment, and conditions involved.

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