Michael Gerard, age 11, of Charleston, w.va., for his question:
What happens when iron rusts?
Iron and steel are sturdy metals, well. Able to perform heavy duties in the world of industry. But outside in the weathery air, these heavy duty metals are always open to attack frown their secret and silent enemy rust. Ships and bridges need constant rust proofing, and sensible owners protect skates and spades and other small items from rust.
Rust attacks iron and steel outdoors where there is rain and dewy moisture in the air. A crumbly coat of reddish brown flakes forms on the surface, and if the metal is not rescued, it soon rusts to dust. The flaky rust is actually ashes and ashes suggest burning. We see no fire as iron and steel rust away, but rusting is actually a burning process.
Coal and wood combine with oxygen to blaze away in a fast and furious burning process. Our bodies use oxygen to change food into energy by a slower burning process. Rust uses oxygen and a little moisture from the air. Since fast or slow burning always uses oxygen, we call it oxidation. And oxidation is a chemical change. It changes the molecules in a fuel into a different set of molecules and leaves only a fragile pile of ashes.
Water quickly douses a fast burning wood fire. But a trace of moisture is needed to start the slow oxidation of iron. Outdoors, raindrops and dewy films of moisture soon gather on the smooth surface of an object made of iron or steel. Conditions are right now for the rusting process to begin. In the presence of moisture, atoms of iron combine with atoms of oxygen from the air.
Iron is the fuel chemical of the slow oxidation called rust. The iron atoms are changed into m01ecules of hydrated iron oxide which is a very different chemical from sturdy iron. It is the reddish brown powder of ashes left from the rusting process. A rough, rusty surface tends to trap and hold moisture even when the air seems to be dry. Once started, the damage continues to bite deeper and deeper into the metal. If left without protection, a massive bridge or ship will finally rust to dust.
The air outdoors provides the oxygen and moisture needed to change iron into rusty iron oxide. The trick of rust proofing is to shield a metal surface from the air. Bridges and ships are protected with constant coats of special paint. Smaller objects of iron and steel can be shielded from rust with heavy coats of oil or grease.
Iron oxide is the rusty dusty enemy of iron and steel. But it is needed by plants and. Animals. Traces of iron present in most soils soon rust into iron oxide, and this chemical is taken in by plants. Our bodies need iron oxide to make rich, red blood, and we get our supplies by eating plenty of salads and green vegetables.