OpenLearn Live normally updates during the day; unfortunately for technical reasons we lost the 4th July edition. In order to ensure we do a 'full set' of our oxide start-up sequence, though, we're slipping this item back into the set.
This week, we're celebrating the world of oxides - chemical compounds that consist of oxygen and just one other element. We're going to start off with one of the more familiar oxides - rust.
Rust is iron oxide - and here's a simple explanation of why iron corrodes in the way it does:
This corrosion of metal is obviously hugely damaging to metal-made things, and anything that's damaging will tend to also be expensive. Back in 2000, it was estimated that corrosion cost the US economy USD300million a year; and when you have cars or bridges or builders that are slowly crumbling away, there can be life-threatening risks as well.
There are ways to prevent or slow rust, though:
- using iron in an alloy specially designed to resist corrosion
- galvanizing - covering the surface of the iron with a thin layer of zinc and/or a zinc alloy
- cathodic protection which uses an electrical current to slow or even stop the corrosion process
- bluing, popular for small steel objects like guns, which covers the surface with a thin layer of oil
- using a corrosion inhibitor
- controling humidity in places where iron or steel is used
- using a protective coating, like paint - a processs known as rustproofing
The latter process is favoured for the Forth Road Bridge. The constant battle between the sea and wind and the bridge meant that the process of rustproofing was never-ending - once the bridge was 'finished', the process needed to be started again. But a new type of paint has - it's hoped - reduced a perpetual task to one only required four times a century. Good news for Sisyphus, who gets to have the 'task that's never finished' metaphor field to himself.