Eli5 Why does oxygen and water cause rust like in veered?

Question

Why does oxygen in the air react with water and cause rust like in vehicles but vehicles in a hot dry desert it slows down the oxidation.

What is it about the oxygen in the air that react with water that causes rust like in vehicles? Why is water so bad?

What is it about water and oxygen in the air that react?

In: 2

Answer 1

There’s two parts to this:

Part 1:

Rust is an electro-chemical reaction. Like a really shitty battery.

The reaction requires the flow of electrons from one place to another. To achieve this you need the two materials to be connected via an electrolyte – a conductive liquid that allows the flow of electrons.

Water, once it dissolves some stuff, provides the electrolyte. If there’s salt in it it provides a much more effective electrolyte as it gets much more conductive. This is why salt greatly accelerates corrosion in iron/steel.

Part 2:

Rust is *hydrated* iron oxide. It’s not just iron reacted with oxygen, but the resulting compound is then attached to several water molecules, part of the reason why rust expands so much compared to the volume of the original material.