Credit to the chemistry textbook for explanation: Tin protects Iron from rusting by acting as a physical barrier against moisture and oxygen. Known as tinning, this method is commonly used for food cans. However, unlike Zinc in galvanized steel, tin is not a "sacrificial" metal. If the tin coating is scratched, the exposed iron rusts rapidly. How the Protection Works Physical Barrier: Tin is highly resistant to natural corrosion. As long as the layer is intact, it prevents oxygen and water from reaching the iron underneath. Reactivity: Tin is less reactive than iron. In the presence of mild acids and atmospheric conditions, it relies entirely on maintaining a flawless coating. Why Scratches Are a ProblemGalvanic Action: When tin-plated iron is scratched and exposed to an electrolyte (like water), an electrochemical cell forms.Iron Corrodes First: Because iron is more reactive than tin, the iron acts as the anode. Instead of protecting the iron, the tin layer causes the exposed iron to corrode even faster than it would on its own. Tin vs. Zinc (Galvanizing)To compare, zinc protects iron sacrificially. If a galvanized piece of metal is scratched, the zinc degrades first, shielding the underlying iron from rust. Tin, on the other hand, only protects the iron when the shield is entirely unbroken.
