How does rust work?

In this episode of BrainStuff, Marshall Brain explains the chemistry behind rust, or iron oxide, and the rusting process.

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Episode Transcript

Speaker 1 (00:00):
Welcome to brainstuff front House, stuff works dot Com, where
smart happens by a Marshall brain with today's question how
does rust work? Rust is the name that we use
for a very common compound iron oxide. Iron oxide, the

(00:24):
chemical F E two O three is common because iron
combines very readily with oxygen, so readily, in fact, that
pure iron is only rarely found in nature. Iron or
steel rusting is an example of corrosion, an electrochemical process
involving an anode, or a piece of metal that readily

(00:46):
gives up electrons, an electrolyte, a liquid that helps electrons move,
and a cathode a piece of metal that readily accepts electrons.
For iron to become iron oxide. Therefore, three things are
acquired iron, water, and oxygen. Here's what happens when the
three get together. When a drop of water hits an

(01:07):
iron object, two things begin to happen almost immediately. First,
the water, a good electrolyte, combines with carbon dioxide in
the air to form weak carbonic acid and even better electrolyte.
As the acid is formed and the iron dissolved, some
of the water will begin to break down into its
component pieces, hydrogen and oxygen. The free oxygen and dissolved

(01:31):
iron bond into iron oxide in a process that frees electrons.
The electrons liberated from the anode portion of the iron
flow to the cathode, which may be a piece of
metal less electrically reactive than iron, or another point on
the piece of iron itself. The chemical compounds found in

(01:52):
liquids like acid rains, seawater, and salt loaded spray from
snow belt roads make them better electrolyte. It's the pure
water allowing their presence to speed the process of rusting
on iron and other forms of corrosion on other metals.
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