Corrosion in iron

Corrosion in iron is what is known as rusting. Chemically, the rusting of iron is an oxidation process. This special property of iron also results in a separation of metals into two groups. All metals that rust like iron are called ferrous metals - all others are called non-ferrous metals. How rust develops, which chemical processes take place here and how you can protect iron from rust, you can read here.

Emergence of rust

For rust to occur, there are only a few basic requirements:

  • The metal in question must be a ferrous metal
  • There must be water (sufficiently high humidity is sufficient)
  • There must be oxygen (also in the air)

When acids are present, iron rust also - but it is then called a so-called hydrogen corrosion. The process of rusting in the air, however, is an oxygen corrosion.

oxygen corrosion

The surrounding oxygen acts chemically as an oxidizing agent. He picks up electrons from the iron. The solid iron is oxidized at the contact surface to divalent iron (Fe2 +). This creates a potential difference because the iron is negatively charged, but its converted surface is now positively charged.

Over several complicated steps arises in the water over the positively charged iron ions, which diffuse there and the diffusing oxygen in each water drop a so-called galvanic cell with a potential difference. Such a galvanic cell is similar in function to a battery.

The flow of current in this chemical "battery" then turns the iron on the surface into ferric hydroxide, which has a typical gray-green color. Further exposure of the ferrous hydroxide to air and water results in iron (III) hydroxide - the rust we immediately recognize by its color.

The oxygen corrosion is therefore a complex process, which takes place in several steps. It can be accelerated by the presence of salts (ions) in the water. This is why iron rust on salty sea air even faster, at least when there is high humidity.

Prevent corrosion

You can not completely prevent corrosion even with iron. However, there are ways to slow them down a lot. Since both oxygen and water are necessary for corrosion, it is sufficient to keep one of the two substances away in order to prevent corrosion for the most part.

In heating pipes made of ferrous metals, this is done by preventing oxygen from entering the pipes. Conversely, keeping tools dry (such as by spraying with talcum powder) does not allow the water to initiate the corrosion process.

Coatings of the iron with chromium or paints or greases are also an option to create a protective layer. Hot-dip galvanizing is also a possibility, especially with iron sheets.

Tips & Tricks

If you store your tool in a damp cellar, simply sprinkle it with powder. Even rust-sensitive tools do not rust then.

Video Board: Rusting of iron