Galvanising

Summary: Coating iron or steel with a layer of zinc to prevent rusting. Zinc provides sacrificial protection even if the coating is scratched. Tags: igcse chemistry definition metals Created: 2026-07-14 Last Updated: 2026-07-14

Galvanising (also spelled galvanizing) is a corrosion-protection technique in which iron or steel objects are coated with a thin layer of zinc metal to prevent rusting. Unlike barrier methods such as painting or greasing, galvanising provides dual protection: the zinc layer acts as a physical barrier excluding oxygen and water from the iron surface, and it also provides sacrificial protection because zinc is more reactive than iron, meaning zinc will oxidise (corrode) preferentially if the coating is scratched, continuing to protect the exposed iron underneath. The zinc is typically applied by hot-dip galvanising, where the steel article is immersed in a bath of molten zinc, forming a strongly bonded zinc-iron alloy layer topped with pure zinc; electroplating can also be used for a thinner, more uniform coat. Galvanised steel is used extensively in outdoor structures such as roofing sheets, fencing, lamp posts, buckets, and car body panels, where long-term corrosion resistance is essential. For IGCSE exams, students must be able to compare galvanising with other rust-prevention methods and explain, using the reactivity series, why zinc provides sacrificial protection while a coating of a less reactive metal such as tin (as in tin-plated food cans) would actually accelerate rusting of the iron if scratched.

Key term — IGCSE Chemistry (0620/0971) glossary.