Q9Engineering Chemistry
Question
2 marks
Why anodic coatings are better than cathodic coatings for corrosion control?
Answer
Anodic coatings protect the base metal sacrificially even if scratched, whereas cathodic coatings accelerate corrosion of the base metal if the coating breaks.
Anodic coatings (e.g., Zinc on Iron / Galvanization) are more reactive than the base metal. If the coating is scratched and the base metal is exposed, the coating continues to act as an anode and corrodes, protecting the base metal (cathodic protection).
Cathodic coatings (e.g., Tin on Iron) are less reactive. They only provide protection as long as they are perfectly intact. If scratched, the exposed base metal becomes a highly localized anode and corrodes extremely rapidly.