Electrochemical passivation
Electrochemical passivation forms a thin, stabilized oxide layer on metal surfaces through anodic polarization. This layer prevents further corrosion and protects the material.
Physico-chemical mechanism of action
Passivation is achieved by applying a positive electric current (anodic polarization) to a metal in a suitable electrolyte. This causes rapid oxidation of the surface, forming a thin, firmly adhering layer. This layer prevents further corrosion by isolating the metal from the surrounding medium.
Metallurgical relevance & risks in welding
Passivation is especially important when processing steels and other metals to increase their corrosion resistance. If applied incorrectly or if passivation is missing, the material can become susceptible to corrosion, leading to cracks and wear. It is also important that passivation is not interrupted, as this can lead to re-initiation of corrosion.
Workshop practice & instructions
To perform successful electrochemical passivation, follow these steps:
1. Surface preparation: The metal must be clean and free of contaminants.
2. Electrolyte selection: Choose a suitable electrolyte, such as a sulfate or nitrate solution, depending on the material to be passivated.
3. Applying voltage: Connect the metal part to the positive terminal of a power source and immerse it in the electrolyte. The voltage should be high enough to cause rapid oxidation.
4. Passivation time: The duration depends on the desired level of protection, but typically ranges from a few minutes to hours.
5. Post-treatment: After passivation, dry the metal and store it in a protected environment if necessary.