A plastic coating that virtually eliminates rust and corrosion could mean cars, bridges and boats that last 10 times as long as they do at the moment.

Called polyaniline, the polymer actually takes part in the rusting process, creating a layer that is almost impervious to the effects of air, water and salt.

Rusting and corrosion occur when metal atoms bond to oxygen, forming oxides that weaken the structure.

This process can be delayed by painting a metal or plating it with zinc.

Zinc, which is a good electron donor, reacts with oxygen, leaving the metal underneath unaffected.

But there is a limit to how long paint and zinc coatings can last.

'Organic metal'

Polyaniline works differently. Instead of creating a physical barrier, it acts as a catalyst that intervenes in the reaction that leads to corrosion.

The polymer takes electrons from the metal and, in turn, gives them to oxygen.

This two-step reaction forms a layer of pure oxide that halts corrosion.

The material is being commercially developed as an anti-rust coating by Ormecon Chemie GmbH & Co at Ammersbek, Germany.

Under controlled laboratory conditions, polyaniline prevented rust 10,000 times more effectively than zinc, creating an "organic metal that could last forever", Ormecon's president Dr Bernard Wessling told a meeting of the American Chemical Society on Sunday.

In field tests, its effectiveness dropped to between three to 10 times that of zinc, but that should still be enough to outlast the usefulness of all but the most permanent structures.

The polymer coating has other advantages over zinc. It is not a heavy metal, which means it has less impact on the food chain and human health.

It is also cheaper than zinc, and can be applied to virtually any metal.

The chemical is already being used for projects in several Asian and European countries, including Japan, Korea, Italy, Germany and France.