More about rusting 1:

Different rusting of iron and of alumnium cans

* Take a Cola can made of iron and
   a second one made of aluminium,
* fill them with a solution of salt dissolved
   in water,* leave them outside for some months.
* As soon as rust holes appear in the cans, cut them to examine them from the inside.

Left photo: The iron can is covered by red brittle rust.
Right photo: The aluminium can is covered by a white jelly.
During rusting iron and aluminium react with air and water. New substances appear.
Rust protection by zinc