Tuesday, 30 July 2013

Where does Rust come from?

Sorry for the long silence, everyone. The weather was really nice here in Britain and I spent a lot of time outside. My friends Tommy and Steve came over and my dad helped us build an awesome treehouse. We pretended to be Aliens who wanted to take over the world from up in our treehouse. Steve even invented a little lift we could use for transporting food and stuff... It was pretty cool!

We also wanted to go on a bike ride through the woods the other day. But when I got out my bike, it was pretty rusty. My parents don't have a lot of money, so they got the bike off one of my cousins when he got a new one last year. It was a very old bike, and when I got it, it already had a few rusty patches. But because we don't have anywhere to put it, I had to keep it outside over the winter (which was really cold and rainy!). And when I got it out for our bike ride the other day, the rust had gotten everywhere...!

There was rust on the chain, on the crank arm, on the handle bars, under the seat and all over the brakes. And when I tried to get it off with the sponge and the old cloth my mom gave me, one of the crossbar clamps came off in my hands and crumbled into a million pieces.

First, I got really upset because I couldn't go on the bike ride with my friends. But then I thought it might be a good idea to find out a little more about rust. Especially because my dad keeps complaining about all the rust on his old VW. He clearly has no idea how to get rid of it properly. So here it goes...

My dad calls rust the 'tin worm', but rust is a chemical reaction and not an animal. When metal rusts, it turns into a compound called 'Iron Oxide'. Iron oxide (Fe2O3) looks a bit like brown and leafy dirt (If you're a real chemistry nerd, you might want to have a look at the whole chemical formula on Chemicalformula.org). The whole process is called 'corrosion' and it happens when metal reacts with water and with oxygen (air). (Check out a few cool experiments with different oxygen levels and rusty steel wool on Physicsinsights.com here.)

Rusting is actually pretty cool. It is a full-on electrochemical process. The metal acts as an anode and the water as the electrolyte of the reaction (check out this video on YouTube for an introduction into electrolytes). When the oxygen in the water reacts with the metal, electrons are set in motion - which then flow to the cathode and convert the metal into rust (the metal also expands - which explains the flaky bits). If you're living close to the sea, sea water makes things even worse because it's got a lot of salt in it. (Higher salt levels make for better electrolyte action.)

Because water and air are pretty much everywhere, it turns out that the only way to prevent metal from rusting is to keep it in a vacuum or to coat it with lots of paint or with corrosion inhibitors. You can also 'galvanize' it with a special zinc coating (they do this with cars). But there are some more advanced techniques that can be used for corrosion protection.

On offshore oil platforms, big oil companies use something called Cathodic Protection to keep their steel from rusting. Instead of letting the structure rust, cathodic protection uses a fake bit of metal as a cathode. Once the first layer is fully covered with rust, it can then protect the rest of the metal because it creates a separate electro-chemical cell. This method is also used in storage tanks and home heating systems. But I don't think it will work on my bike or on my dad's VW because I don't think he will want to drive around in a car that's totally covered in rust...

If my parents had more money, I would ask them to buy me a bike with a full aluminum frame. Some people think aluminum can't rust but that's wrong. It does. But when it does, the rust on top looks a lot like the original aluminum because it's grey. It acts as a natural galvanizer and protects the surface from further corrosion.

I think I will have to sand off the rust on my bike and then put some zinc primer (which is a lighter version of cathodic protection) and some paint on it. This is also what my dad should do with his VW. I hope he has one of those masks people use for painting because some of the stuff I found online seems pretty potent. I don't think he should do this alone. He's not very good with technical things and I don't want him to go blind or faint...

The alien picture came from a website called Sodahead.com. The VW picture is from a project I found on TheSamba.com. The oil platform came from a website on rust protection and anti-corrosion paints www.aquasteel.co.uk).