【Basic Knowledge 30】Galvanic Corrosion (Prize Quiz)

Local corrosion at the contact points of different metals in the same medium, caused by differences in corrosion potentials, is known as galvanic corrosion. These two metals form a galvanic cell, generating an electromotive force that increases the dissolution rate of the metal with the lower potential (the anode) and decreases the dissolution rate of the metal with the higher potential (the cathode).

When two different metals come into direct contact in a solution, their differing electrode potentials create a corrosion cell, resulting in the dissolution and corrosion of the metal with the more negative electrode potential. This type of corrosion is known as galvanic corrosion, or contact corrosion, or bimetallic corrosion. When it is necessary in engineering for two metal materials to be in contact, metal materials that are placed close to each other can be selected based on the measured electromotive force sequence, in order to reduce their potential difference and thereby minimize electrochemical corrosion. Corrosion conditions: 1) Two different metals are in direct contact within the solution ； (Solution factors) 2) There is a difference in electrode potential between the two different metals ； (Potential factors) 3) The spatial arrangement between the two different metals as a couple (geometric factors). Electrode corrosion cannot occur without one of these factors.

Due to different corrosion potentials, local corrosion occurs at the contact points between dissimilar metals in the same medium.

Couples corrosion, also known as dissimilar metal corrosion or contact corrosion, refers to the phenomenon in which, when two materials with different electrochemical properties form a circuit with the surrounding environmental medium, the corrosion rate of the metal with the more positive potential slows down, while the corrosion rate of the metal with the more negative potential accelerates. The reason for this phenomenon is the potential difference between these two materials, which creates a macroscopic corrosion galvanic cell.

When two different metals come into direct contact in a solution, their differing electrode potentials create a corrosion cell, resulting in the dissolution and corrosion of the metal with the more negative electrode potential; this type of corrosion is known as galvanic corrosion

Local corrosion at the contact points between different metals in the same medium occurs due to differing corrosion potentials; this is known as galvanic corrosion

The concept of galvanic corrosion. When two different metals are immersed in a conductive solution, there is usually a potential difference between them. If these metals come into contact with each other (or are connected by a wire), this potential difference causes electrons to flow between the metals. Metals with poor corrosion resistance act as the anode, leading to increased corrosion, while metals with high corrosion resistance act as the cathode, reducing corrosion. This type of corrosion pattern is known as galvanic corrosion

Couples corrosion, also known as dissimilar metal corrosion or contact corrosion, refers to the phenomenon in which, when two materials with different electrochemical properties form a circuit with the surrounding environmental medium, the corrosion rate of the metal with the more positive potential slows down, while the corrosion rate of the metal with the more negative potential accelerates. The reason for this phenomenon is the potential difference between these two materials, which creates a macroscopic corrosion galvanic cell. As a common form of corrosion, galvanic corrosion can induce or even accelerate the occurrence of corrosion processes such as stress corrosion, pitting corrosion, crevice corrosion, and hydrogen embrittlement. Three basic conditions must be present simultaneously for galvanic corrosion to occur: First, there must be materials with different corrosion potentials; the driving force behind galvanic corrosion is the potential difference that arises between the metal being corroded and the highly corrosive metal or non-metal to which it is electrically connected ； Second, there is an ionic conduction path; the electrolyte must be continuously present between the contacting metals to form the ionic conduction path of the galvanic corrosion cell ； Third, there is an electronic conduction path, namely a direct contact between the corroded metal and a metal or non-metal with a higher potential, or an electrical connection achieved through other electronic conductors, which constitutes the electronic conduction path of the corrosion cell.

Galvanic corrosion occurs when two different metals come into direct contact in a solution; due to their differing electrode potentials, a corrosion cell is formed, resulting in the dissolution and corrosion of the metal with the more negative electrode potential. Couples corrosion can also occur in the same metal due to potential differences resulting from surface impurities, oxide films, and different media.

When two metals are immersed in a corrosive solution, and due to the potential difference between them, if they come into contact with each other, a corrosion cell is formed