News release

From: Springer Nature

Chemistry: Electrically charged raindrops promote corrosion

Electrically charged raindrops, a naturally occurring phenomenon, can break down surfaces that have been treated with protective coatings, according to research published in Nature. This previously overlooked corrosion mechanism highlights a need for a new method of preserving metal objects like cars, ships, buildings, and cultural heritage sites.  

Corrosion is an economic and safety issue for outdoor metal products and structures. Corrosion from rain was thought to be predominantly caused by the drops being physically abrasive or acidic from pollutants. While previous research has demonstrated that water drops can become electrically charged after sliding over common surfaces like plant leaves and window glass, the role of that charge in corroding metal surfaces was overlooked.  

Rüdiger Berger, Hans-Jürgen Butt and colleagues analysed how electrically neutral water drops can become charged and corrode different materials. They dropped water onto four common surfaces — a plant leaf, PVC (polyvinyl chloride) foam board, polystyrene glass, and a commonly used water-repelling coating called PFOTS (perfluorooctadecyltrichlorosilane). The drops then slid onto Teflon-coated copper. The authors found that drops acquired a tiny electrical charge (between 0.2 and 2 nanocoulombs). Observations made after 3,000 drops fell from the surfaces to the Teflon-coated copper found that the coating broke down, leading to corrosion of the underlying metal. When the drops had no charge, no surface damage was observed.  

Further research is needed to investigate how to suppress corrosion under these conditions and improve materials designed to protect ships, cars, and buildings.