Raymond Lozano, age 10, of Ottawa., Ontario, for his question:
How does rust make holes in metal?
Rust is the great enemy of iron and steel. It attacks these and other metal objects left outdoors, especially when the air is damp. For this reason we do not leave hoes, rakes and other tools in the garden. If we leave an iron tool outdoors all winter, chances are it will be flaked with rust and maybe pitted with holes come spring. So, let's return all our metal tools to the warm, dry cellar. For extra protection we can smear a film of grease or oil over the metal parts. Nowadays you can even buy a plastic coating to protect metal objects from rust so there is no excuse for letting these objects become ruined.
Strange to say, rust is a junior cousin of the fire in the grate. Both are chemical reactions in which oxygen plays a very active part. The fuel, the metal and the gases in the air are the chemicals which take part in this process, which we call oxidation. Oxidation may be a brisk fire or the slower rusting of a metal hoe. It is also the slow burning which goes on inside our bodies when nourishment is changed into energy.
Iron is a chemical element, very plentifully strewn throughout the rocks of the earth's crust. However, we never find great layers of pure iron in the earth. In fact, pure iron is very rare in nature, This is because iron rusts in damp air. Damp air contains dissolved oxygen and the oxygen must be dissolved in water before it can set off the oxidation or rusting process in the metal.
The slow burning begins when a drop of moisture falls upon an iron surface. For a few minutes, the water remains clear. Then it becomes a fuzzy green color. Later it turns to a rusty brown.
During this process, atoms of iron have combined with the dissolved oxygen to form molecules of iron oxide. Iron oxide, or rust, is a reddish brown chemical very different from the hard~iron and also very different from oxygen.
As the moisture evaporates from the metal surface, the rusty spot is left behind. A little pocket of the hard iron is now flaky iron oxide Water tends to rush off a hard, shiny surface, like that of the original iron. But it tends to cling to a rough or porous surface like the spot of rust which provides the moisture with a spongy pocket. This brings more dissolved oxygen in contact with the iron metal. More iron becomes rusty iron oxide. The original spot of rust grows and grows.
Once started, rust is very hard to stop. All the rusty spots must be buffed away and the metal left quite smooth again. It is far easier to prevent rust than to treat it after it has eaten into a metal object.