Rust Is Iron Oxide, and It Weighs More Than the Iron Did
An oxide is a compound of oxygen with another element. Rusting adds oxygen to iron, so rusted metal is heavier.
An oxide is a chemical compound containing oxygen bonded to another element. Rust is iron oxide, and it is heavier than the iron it replaced: oxygen atoms from the air join the metal, so a fully rusted object weighs more than the original. That fact helped disprove the old phlogiston theory, which held that burning released a substance and should therefore reduce weight. Aluminium also forms an oxide, but its layer is thin, tight and protective, which is why aluminium does not corrode away.
- An oxygen compound. *Iron oxide.*
- Rust — iron oxide. *Covered in rust.*
- Oxidise — to combine with oxygen. *It oxidises.*
- Aluminium oxide — a protective layer. *Aluminium oxide.*
- Oxygen — the element. *Oxygen.*
Word forms
| Form | Word | Example |
|---|---|---|
| Noun | oxide | An oxide. |
| Plural | oxides | Metal oxides. |
| Verb | oxidise | It oxidises. |
| Noun | oxidation | Oxidation. |
| Greek | oxys | Sharp, acid. |
- Rust is a form of iron oxide.Chemistry.
- Rusted iron weighs more than clean iron.Fact.
- Aluminium oxide protects the metal.Contrast.
Why aluminium does not rust away
- Aluminium oxidises instantly on contact with air
- Its oxide layer is dense and bonds tightly to the surface
- That layer seals the metal from further attack
- Iron oxide is flaky, exposing fresh metal underneath
- Anodising deliberately thickens the aluminium oxide layer
French *oxide*, coined in 1787 from *oxygène* plus *acide*, from Greek *oxys*, sharp or acid.
Does rusted iron weigh more?
Yes. Oxygen from the air bonds to the metal, so the rusted object is heavier than the iron it started as.
Why does aluminium not corrode like iron?
Its oxide layer is dense and bonds tightly, sealing the metal. Iron oxide flakes away and exposes fresh metal.