Raindrops are tiny lightning bolts, and they’re corroding cars, study finds
摘要
新研究揭示，雨滴在撞击表面时携带的电荷足以击穿绝缘涂层，而不仅是传统认为的溶解或磨损。德国马普高分子研究所团队发现，水滴在绝缘表面滑动时会产生“滑动起电”效应，电压最高可达9000伏，能像电火花一样在涂层上打出孔洞，从而加速金属腐蚀。这一发现挑战了现有防腐机制的理解，或为改进涂料和防护技术提供新方向。
The standard explanation for why rain causes corrosion is that water carries dissolved salts and acids to a surface, constant drumming of raindrops abrades whatever protective coating is on it, and oxygen does the rest. Nearly all our tools to prevent this—paints, polymer films, or oxide layers—are built around this idea. But we’ve apparently been missing something important about the rain.
A new study led by Zhongyuan Ni, Rüdiger Berger, and Hans-Jürgen Butt at the Max Planck Institute for Polymer Research in Mainz, Germany, has shown that water drops routinely arrive at a surface carrying an electrical charge large enough to punch through an insulating coating. Not scratch it. Not slowly dissolve it. Electrically blow a hole in it, the way a spark jumps a gap.
Charged rain
The starting point of the study is a phenomenon called "slide electrification," which has only been properly quantified in the past few years. When a water drop slides across an insulating surface like a leaf, a painted wall, a windowpane, or a plastic panel, it strips charge from that surface and leaves an opposing charge behind. The voltages involved are not trivial. Drops charged this way have been measured at up to 9,000 volts.
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