Raindrops are tiny lightning bolts, and they’re corroding cars, study finds

A new study from the Max Planck Institute for Polymer Research in Mainz, Germany, has revealed that raindrops carry a significant electrical charge as they strike a surface, potentially causing corrosion more quickly than previously thought. The research, led by Zhongyuan Ni, Rüdiger Berger, and Hans-Jürgen Butt, challenges the traditional understanding of rain's role in corrosion.

Slide electrification, the phenomenon where a water droplet slides across an insulating surface and strips away its charge, has only recently been quantified. The voltages generated by this process can reach up to 9,000 volts, which is substantial enough to "electrically blow a hole in it, the way a spark jumps a gap," according to the study.

Unlike the conventional explanation that water carries dissolved salts and acids, causing corrosion through abrasion and oxidation, the charged raindrops directly puncture insulating coatings. This shift in understanding suggests that our current methods of preventing corrosion, such as paints, polymer films, and oxide layers, may need to be reevaluated. The study emphasizes the need to account for the electrical charge carried by raindrops when developing strategies to protect surfaces from corrosion.