What type of corrosion occurs in graphite when it is in contact with stainless steel?
Microbial corrosion
Crevice corrosion
Pitting corrosion
High temperature corrosion
The graphite undergoes pitting corrosion in stainless steel. The creation of the small holes on the surface of the metal is called pitting corrosion.
When graphite comes into contact with stainless steel, the type of corrosion that can occur is called galvanic corrosion, which can lead to localized corrosion such as crevice corrosion and pitting corrosion.
Galvanic corrosion happens when two dissimilar metals are in contact with each other in the presence of an electrolyte, such as water or an acidic solution. In this case, graphite and stainless steel are two different metals with different electrochemical potentials, meaning they have different tendencies to lose or gain electrons. When they are in contact with each other in the presence of an electrolyte, an electrochemical reaction can occur where one metal (the anode) loses electrons and corrodes, while the other metal (the cathode) gains electrons and is protected from corrosion.
In the case of graphite and stainless steel, graphite is the anode, meaning it will corrode and release electrons, while stainless steel is the cathode, meaning it will be protected from corrosion. This can lead to localized corrosion such as crevice corrosion and pitting corrosion, where the corrosion occurs in areas where the two metals are in contact or where the electrolyte is trapped.
Crevice corrosion occurs in small, confined spaces such as gaps between two materials, where the oxygen and other chemicals required for the electrochemical reaction are limited. Pitting corrosion, on the other hand, is a form of localized corrosion where small pits or craters form on the surface of the metal. These types of corrosion can be accelerated when graphite is in contact with stainless steel due to galvanic corrosion.
It is important to note that high temperature corrosion is not typically associated with the contact between graphite and stainless steel, as it usually occurs at much higher temperatures than those encountered in typical operating conditions for these materials.