Home >> Science & Nature >> Science

How Can Oxygen Affect Iron?

Oxygen's effect on iron can be summed up in one word: rust.

Rust is a form of corrosion --- the chemical reaction that occurs when oxygen bonds with metal atoms. If you've walked through a junkyard or left a screwdriver outside for several days, you've seen how oxygen in the air around us affects iron and its derivatives, such as steel.

How Rust Forms
- Rust is the name for a common compound: iron oxide. Two things are required for iron to change into iron oxide: water and oxygen. When moist air touches iron, the oxygen reacts with iron to form iron oxide. The amount of water present affects the color of the rust, which can be yellow, brown or black. Iron oxide flakes easily, exposing more iron to the corrosion process. Eventually the metal weakens and disintegrates.
Factors Affecting Corrosion
- The environment greatly affects the rate of corrosion.
  
  The environment and the presence of other chemicals affect the corrosion rate of iron and steel. Moisture speeds up corrosion, so rust is more prevalent in the humid plains of the Midwest than in the dry deserts of the southwestern U.S. Salt also increases corrosion rates by improving the conductivity of water along a metal surface. If you drive a car to the seashore or through icy streets treated with salt, it will rust more quickly than if you drive it in an arid, salt-free environment, such as a desert.
Slowing the Process
- An exterior of stainless steel helps the Gateway Arch in St. Louis resist corrosion.
  
  Protecting iron from water and oxygen can help slow the corrosion process. Such protection takes two main forms --- coating and alloying the metal. Workers might coat iron or steel with another metal, such as zinc, or apply a layer of resin, paint, enamel or grease. In the alloying process, iron is combined with another metal that is less prone to oxidation. Stainless steel, which has a thin protective layer of chromium sesquioxide, is produced by the fusion of steel with chromium and nickel.
Case in Point: The Golden Gate Bridge
- The Golden Gate Bridge must be continuously maintained to prevent rust.
  
  The Golden Gate Bridge, one of the world's longest suspension bridges, was completed in 1937. More than 1.5 billion vehicles have used it to cross San Francisco Bay. Constantly exposed to salt and water from the sea, the bridge continually is monitored for rust. Workers prime and paint it when needed. When rust appears, they cut out the corroded pieces and replace them.

Science