Polyaniline coating for metals ‘three times better than zinc’

For decades metals have been galvanised or painted to prevent rust. A new polymer may be about to change all that.

Used as a coating, the new plastic eliminates rust and corrosion to such a degree that cars, bridges and boats could last 10 times as long as they do now.

Developed by German firm Ormecon Chemie, in Ammersbek, the polymer, known as a polyaniline, takes part in the rusting process, creating a stable layer that is resistant to the effects of air, water and salt. Rusting and corrosion occur when metal atoms bond with oxygen, forming oxides. In the case of iron or steel, the oxide flakes off, eroding and weakening the structure. This process can be delayed by painting the metal or galvanising it with zinc. With other metals, such as aluminium, a film of oxide forms on the surface but stays there, preventing progressive corrosion.

The polyaniline makes steel behave more like aluminium, acting as a catalyst, and intervening in the reaction that leads to corrosion. The polymer takes electrons from the metal and binds them to oxygen, but the layer of oxide so formed is stable and does not flake away, halting further corrosion. In laboratory conditions, the company claims polyaniline prevented rust 10,000 times more effectively than zinc. In field tests, its effectiveness dropped as low as just three times that of zinc, yet that would still be enough to keep metal products in pristine condition long after they are practically obsolete.