Does zinc rust?
Iron, for example, reacts with water and oxygen in the atmosphere to form hydrated iron (III) oxide on the surface of the metal. This corrosion product, which is referred to as "rust," is known for its reddish-brown color as well as its damaging effects. Hydrated iron oxides are brittle and flake away easily, thus exposing more of the underlying metal to the atmosphere for further corrosion. This cycle repeats itself until the iron is fully consumed by the corrosion process.
Zinc, on the other hand, reacts with oxygen to form a thin oxide layer. This layer then reacts with moisture to produce zinc hydroxide, which further reacts with carbon dioxide to create zinc carbonate. Unlike iron oxides, which flake off easily, zinc carbonate is resilient, chemically stable, and adheres firmly to the surface of the metal. This layer acts as a protective barrier that prevents air and moisture from contacting the underlying substrate and prevents further corrosion and deterioration.
While the carbonate layer has protective properties, zinc is a reactive metal and will slowly erode due to corrosion over time. The rate of corrosion of zinc is, however, 1/30 that of steel. Therefore, zinc metals and components coated with zinc-based products have a significantly longer service life than other metals when exposed to the atmosphere. Zinc rich coatings are used in a process known as cold galvanizing to prevent corrosion. (Learn more about galvanizing in the article Hot-dip vs Cold Galvanizing: What’s the Difference?)
Zinc may also exhibit a type of corrosion known as white rust. This type of rust occurs when zinc surfaces have not had enough time to fully develop the protective carbonate layer. Instead, the surface remains with a zinc hydroxide layer, which has a white, powdery appearance. This typically occurs due to a lack of free-flowing air over the zinc surface. However, white rust is usually considered to be superficial and can be remedied by exposing the rust deposits to free-flowing air or by removing it with light brushing.
Other metals that form protective oxide layers similar to zinc include aluminum, copper, chromium and titanium. (See 3 Truths About Titanium Dioxide Corrosion Prevention for more information.)
More Q&As from our experts
- Why do zinc rich primers sometimes leave a powdery topcoat?
- Does aluminum rust?
- Are there some anti-corrosion applications in which airless spraying is a bad idea?
- Zinc Carbonate
- Zinc Hydroxide
- Zinc Anode
- Zinc Oxide
- Galvanic Coating
- White Rust
- Oxide Layer
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