Raindrops Carry Electrical Charge, Causing Corrosion by Punching Holes in Coatings

New Corrosion Mechanism Identified

Researchers at the Max Planck Institute for Polymer Research, led by Zhongyuan Ni, Rüdiger Berger, and Hans-Jürgen Butt, have discovered a previously unrecognized mechanism for rain-induced corrosion. Their study indicates that water drops routinely carry a significant electrical charge upon impact with a surface, capable of creating holes in insulating coatings.

Electrical Puncture, Not Abrasion or Dissolution

The conventional understanding of rain corrosion involves water carrying dissolved substances, abrasive action from drops, and oxygen. However, this new research suggests that the electrical charge on raindrops can directly punch through protective layers, similar to a spark, rather than slowly dissolving or abrading them. This electrical breakdown represents a distinct mode of material degradation.

The Role of Slide Electrification

The study's foundation is the phenomenon of "slide electrification," where a water drop sliding across an insulating surface acquires an electrical charge by stripping electrons from that surface. Measurements have shown that drops charged through this process can reach voltages as high as 9,000 volts. This substantial charge is sufficient to overcome the dielectric strength of many protective coatings.

Implications for Protective Coatings

This discovery suggests that current corrosion prevention methods, which primarily focus on chemical resistance and physical abrasion, may be incomplete. Understanding the electrical nature of raindrop impact could lead to the development of new types of paints, polymer films, and oxide layers designed to resist electrical punctures, thereby improving the longevity of materials exposed to rain.