Definition - What does Cathodic Modification mean?
Cathodic modification is an anodic reaction retardation which results from the enhanced capability of alloys to undergo passivation through the active cathode introduction in the alloy. It is one method that allows production of alloys that are resistant to corrosion since the alloys' resistance from electrochemical attack is enhanced.
Cathodic modification is typically seen with alloying titanium and stainless steel with certain metals such as the platinum group.
Corrosionpedia explains Cathodic Modification
In the corrosion process, there are different ways wherein alloys that are resistant to corrosion can be formed or electrochemical attack resistance can be enhanced. These include:
- Increased thermodynamic stability
- Kinetic retardation involving the anodic process
- Kinetic retardation involving the cathodic process
- Generation of passivating and stable oxide layers
Thermodynamic stability involving steel can be elevated in limited cases. For instance, steel that contains chromium can be alloyed with molybdenum or nickel. Also, retardation of cathodic reaction can be done in several ways, like eradication of active positive impurities as well as increasing the cathodic process overvoltage. Examples of this are alloying metals like zinc or manganese to magnesium and antimony or arsenic to steel.
Passivating layers can be achieved through the addition of chromium, which is less stable relative to iron in terms of thermodynamics. Stainless steel technically derives its resistance to corrosion to the passivating oxide layers on top of the steel. Meanwhile, anodic reactions can be slowed down in many ways, like alloying nickel and iron steels with metals like chromium. This can also be achieved by the introduction of active cathodes into the alloy. One good example is alloying titanium and stainless steel with platinum-group metals (PGMs). This technique is referred to as cathodic modification.
In order to achieve cathodic modification, these requirements should be fulfilled:
- The base alloy should contain critical current density.
- The passivation potential of the base metal must be negative to permit the cathodic component to modify the corrosion potential.
- The base alloy's transpassive potential must be electropositive for a broader passive range.
- The cathodic alloying material should have lower overvoltage and higher current density and must be resistant to corrosion under the situation.