Ways to prevent rust

Oh-oh! Looks like this bicycle was left outside for too long. The metal has turned brown, porous, and is flaking away. It has rusted! Or, to use a chemistry term, it has corroded.

Three things must be present for an object to rust: Iron - which is the main component of steel. Oxygen - of which there is plenty in the air. And a little bit of water! The water itself isn't an ingredient of the rust. But it's needed for the iron to react with oxygen.

There are many ways to prevent rust from forming! The simplest thing you can do is to coat the metal with paint or lacquer. This keeps oxygen and water from getting in contact with the iron. As long as the paint covers all the metal, and no air can sneak in, the bicycle is protected! But even a tiny scratch is enough to let some oxygen and moisture in.

Once the rust starts forming, it grows -- it expands -- and pushes more of the paint off. And since rust is porous... more oxygen and moisture can enter the metal, and the rusting continues to eat down into the metal. Some parts of the bicycle move and grind against each other. Like the chain and the gears.

For these parts, it's better to use oil or grease to keep water and air away from the metal. But look at this bolt here! It's not painted, and it's not covered in grease, but it still hasn't rusted at all! This bolt is made of stainless steel. Stainless steel is a mixture of metals -- an alloy.

The metal added in this alloy, that makes it resistant to rust is chromium. A cool thing with stainless steel, is that it corrodes too, just like iron! But unlike rust, the corrosion that forms on stainless steel isn't porous. Instead, the corrosion itself forms a hard barrier, that can't be penetrated by air or water vapour. An even fancier way to use chromium to protect against rust, is to cover the steel part entirely in a thin layer.

Handlebars on bicycles and the tail pipes of motorbikes are often covered with chromium -- they are chrome-plated. There are other ways to prevent rust. Here's one that isn't used on bicycles at all. Remember that rusting is an electro-chemical reaction that starts with the iron releasing some of its electrons to the oxygen? To prevent the oxygen from stealing the iron's electrons we can add another metal that is even more eager to give away its electrons.

Zinc is such a metal. Zinc is really bad at holding onto its electrons. So we put a big bar of zinc on onto the hull of a ship, in contact with the iron... If the oxygen in the water starts to steal electrons from the iron, then the zinc will be quick to offer up its electrons instead, so the zinc will corrode instead of the iron. For that reason, these zinc bars are called sacrificial anodes. (An anode is something that wants to give off electrons, but we'll deal with that another time.) The same method can be used on small things as well, like a nail.

In that case, we cover the entire nail in a layer of zinc. We say that the nail is galvanized. Rust is the common name for when iron corrodes. Three things are needed for rusting to occur: Iron, oxygen, and water. Here are three ways to prevent rust: One: Keep oxygen and water away from the iron.

Two: Mix the iron into an alloy with chromium, which resists corrosion better. And three: Connect the iron with a metal that will sacrifice its electrons, before the iron does.